Understanding Nutrition [5 Australian and New Zealand ed.] 0170457974, 9780170457972

Table of contents :
Title Page
Imprint Page
Contents in Brief
Contents
Guide to the text
Guide to the online resources
Preface
About the authors
Acknowledgements
Chapter 1: An overview of nutrition
1.1 Food choices
1.2 Nutrients
1.3 The science of nutrition
1.4 Nutrient Reference Values
1.5 Nutrition assessment
1.6 Diet and health
Chapter activities
Highlight 1: Nutrition information and misinformation: on the net and in the news
Chapter 2: Planning a healthy diet
2.1 Principles and guidelines
2.2 Diet-planning guides
2.3 Food labels
Chapter activities
Highlight 2: Vegetarian diets
Chapter 3: Digestion, absorption and transport
3.1 Digestion
3.2 Absorption
3.3 The circulatory systems
3.4 The health and regulation of the GI tract
Chapter activities
Highlight 3: Common digestive problems
Chapter 4: The carbohydrates: sugars, starches and dietary fibre
4.1 Chemical structure of carbohydrates
4.2 The simple carbohydrates
4.3 The complex carbohydrates
4.4 Digestion and absorption of carbohydrates
4.5 Glucose in the body
4.6 Health effects and recommended intakes of sugars
4.7 Alternative sweeteners
4.8 Health effects and recommended intakes of starch and dietary fibre
Chapter activities
Highlight 4: Carbs, kilojoules and controversies
Chapter 5: The lipids: triglycerides, phospholipids and sterols
5.1 Chemical structure of fatty acids and triglycerides
5.2 Chemical structure of phospholipids and sterols
5.3 Digestion, absorption and transport of lipids
5.4 Lipids in the body
5.5 Health effects and recommended intakes of saturated fats, trans fats and cholesterol
5.6 Health effects and recommended intakes of monounsaturated and polyunsaturated fats
5.7 From guidelines to groceries
Chapter activities
Highlight 5: High-fat foods: friend or foe?
Chapter 6: Protein: amino acids
6.1 Chemical structure of proteins
6.2 Digestion and absorption of protein
6.3 Proteins in the body
6.4 Protein in foods
6.5 Health effects and recommended intakes of protein
Chapter activities
Highlight 6: Nutritional genomics
Chapter 7: Metabolism: transformations and interactions
7.1 Chemical reactions in the body
7.2 Breaking down nutrients for energy
7.3 Feasting and fasting
Chapter activities
Highlight 7: Alcohol in the body
Chapter 8: Energy balance and body composition
8.1 Energy balance
8.2 Energy in: the kilojoules foods provide
8.3 Energy out: the kilojoules the body expends
8.4 Body weight, body composition and health
8.5 Health risks associated with body weight and body fat
Chapter activities
Highlight 8: Eating disorders
Chapter 9: Weight management: overweight, obesity and underweight
9.1 Overweight and obesity
9.2 Causes of overweight and obesity
9.3 Problems of overweight and obesity
9.4 Aggressive treatments for obesity
9.5 Lifestyle strategies
9.6 Underweight
Chapter activities
Highlight 9: The latest and greatest weight-loss diet – again
Chapter 10: The water-soluble vitamins: B group vitamins and vitamin C
10.1 The vitamins: an overview
10.2 The B group vitamins: as individuals
10.3 The B group vitamins: in concert
10.4 Vitamin C
Chapter activities
Highlight 10: Vitamin and mineral supplements
Chapter 11: The fat-soluble vitamins: A, D, E and K
11.1 Vitamin A and beta-carotene
11.2 Vitamin D
11.3 Vitamin E
11.4 Vitamin K
Chapter activities
Highlight 11: Vitamin D and good health
Chapter 12: Water and the major minerals
12.1 Water and the body fluids
12.2 The minerals: an overview
12.3 Sodium
12.4 Chloride
12.5 Potassium
12.6 Calcium
12.7 Phosphorus
12.8 Magnesium
12.9 Sulphate
Chapter activities
Highlight 12: Osteoporosis and calcium
Chapter 13: The trace minerals
13.1 The trace minerals: an overview
13.2 Iron
13.3 Zinc
13.4 Iodine
13.5 Selenium
13.6 Copper
13.7 Manganese
13.8 Fluoride
13.9 Chromium
13.10 Molybdenum
13.11 Other trace minerals
Chapter activities
Highlight 13: Phytochemicals and functional foods
Chapter 14: Fitness: physical activity, nutrients and body adaptations
14.1 Fitness
14.2 Energy systems and fuels to support activity
14.3 Vitamins and minerals to support activity
14.4 Fluids and electrolytes to support activity
14.5 Diets for physically active people
Chapter activities
Highlight 14: Supplements as ergogenic aids
Chapter 15: Life cycle nutrition: pregnancy and lactation
15.1 Nutrition prior to pregnancy
15.2 Growth and development during pregnancy
15.3 Maternal weight
15.4 Nutrition during pregnancy
15.5 High-risk pregnancies
15.6 Nutrition during lactation
Chapter activities
Highlight 15: Foetal alcohol syndrome
Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
16.1 Nutrition during infancy
16.2 Nutrition during childhood
16.3 Nutrition during adolescence
Chapter activities
Highlight 16: Childhood obesity and the early development of chronic diseases
Chapter 17: Life cycle nutrition: adulthood and the later years
17.1 Nutrition and longevity
17.2 The ageing process
17.3 Energy and nutrient needs of older adults
17.4 Nutrition-related concerns of older adults
17.5 Food choices and eating habits of older adults
Chapter activities
Highlight 17: Nutrient–drug interactions
Chapter 18: Diet-related disease
18.1 Nutrition and infectious diseases
18.2 Nutrition and chronic diseases
18.3 Cardiovascular disease
18.4 Hypertension
18.5 Diabetes mellitus
18.6 Cancer
18.7 Recommendations for chronic disease prevention
Chapter activities
Highlight 18: Complementary and alternative medicine
Chapter 19: Concerns about foods and water
19.1 Food safety and food-borne illnesses
19.2 Environmental contaminants
19.3 Natural toxins in foods
19.4 Pesticides
19.5 Food additives
19.6 Consumer concerns about water
Chapter activities
Highlight 19: Food biotechnology
Appendix A Cells, hormones and nerves
Appendix B Basic chemistry concepts
Appendix C Biochemical structures and pathways
Appendix D Measures of protein quality
Appendix E Nutrition assessment
Appendix F Physical activity and energy requirements
Appendix G Aids to calculation
Answers
Glossary
Index

Citation preview

5TH

AUSTRALIAN & NEW ZEALAND EDITION

Understanding Nutrition Eleanor Whitney, Sharon Rady Rolfes, Tim Crowe, Adam Walsh

5TH

AUSTRALIAN & NEW ZEALAND EDITION

Walnuts are a rich source of heart-healthy omega-3 fatty acids Beta-carotene gives carrots their orange colour while also helping our vision

The lycopene in tomatoes gives them their red colour and is a natural antioxidant

Understanding Nutrition Compounds in ginger can help reduce feelings nausea Rady ofRolfes,

Eleanor Whitney, Sharon Tim Crowe, Adam Walsh

Understanding Nutrition 5th Edition Eleanor Whitney Sharon Rady Rolfes Tim Crowe Adam Walsh

Portfolio manager: Fiona Hammond Product manager: Michelle Aarons Content developer: Stephanie Davis Project editor: Raymond Williams Cover design: Emilie Pfitzner (Everyday Ambitions) Text designer: Cengage Creative Studio (original design by Danielle Maccarone) Permissions/Photo researcher: Catherine Kerstjens Editor: Jade Jakovcic Proofreader: James Anderson Indexer: Max McMaster Cover: unsplash/Jocelyn Morales; unsplash/Mockup Graphics; unsplash/Mockup Graphics; unsplash/Tamanna Rumee Typeset by KnowledgeWorks Global Ltd Any URLs contained in this publication were checked for currency during the production process. Note, however, that the publisher cannot vouch for the ongoing currency of URLs. Fourth edition published by Cengage in 2019 Authorised adaptation of Whitney & Rolfes, Understanding Nutrition 16e, 9780357447512 Acknowledgements Chapter opener image credits: Ch1 Opener: Sliced purple onion: Adobe Stock/alinakho; Ch1 Inset: Slices thick purple onion: Adobe Stock/xamtiw; Ch2 Opener and inset: Lemon segments: Adobe Stock/filistimlyanin1; Ch3 Opener and inset: Sliced fresh vegetables and whole radish: Adobe Stock/9dreamstudio; Ch4 Inset: Cashew nuts: Adobe Stock/xamtiw; Ch5 Opener and inset: Yellow watermelon: Adobe Stock/Flaffy; Ch5 End of chapter design: Yellow and pink watermelon: Adobe Stock/Flaffy; Ch6 Opener and inset: Spinach leaves: Adobe Stock/ Flaffy; Ch7 Opener and inset: Button mushrooms: Adobe Stock/filistimlyanin1; Ch8 Opener: Banana bunches: Adobe Stock/mariaaverburg; Ch8 Inset: Sliced banana: Adobe Stock/Yeti Studio; Ch9 Opener and inset: Sliced beetroot, leek and cucumber: Adobe Stock/8H; Ch10 Opener and inset: Dried pasta shapes: Adobe Stock/Agnes; Ch11 Opener and inset: Blueberries: Adobe Stock/filistimlyanin1; Ch12 Inset: Mandarin segments: Adobe Stock/ChaoticDesignStudio; Ch12 Opener: Mandarin and segments pattern: Adobe Stock/filistimlyanin1; Ch13 Opener and inset: Mixed vegetables: Adobe Stock/ Flaffy; Ch14 Opener: Coconuts: Adobe Stock/MOVA; Ch14 Inset: Coconut swirls: Adobe Stock/OlgaKot20; Ch15 Opener and inset: Avocados: Adobe Stock/filistimlyanin1; Ch16 Opener and inset: Cherries: Adobe Stock/Flaffy; Ch17 Opener and inset: Various green fruit and vegetables: Adobe Stock/Tatiana Morozova; Ch19 Opener: Sliced cucumber, in rows: Adobe Stock/Ksenia; Ch19 Inset image: Sliced cucumber: Adobe Stock/Sergey

© 2023 Cengage Learning Australia Pty Limited Copyright Notice This Work is copyright. No part of this Work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means without prior written permission of the Publisher. Except as permitted under the Copyright Act 1968, for example any fair dealing for the purposes of private study, research, criticism or review, subject to certain limitations. These limitations include: Restricting the copying to a maximum of one chapter or 10% of this book, whichever is greater; providing an appropriate notice and warning with the copies of the Work disseminated; taking all reasonable steps to limit access to these copies to people authorised to receive these copies; ensuring you hold the appropriate Licences issued by the Copyright Agency Limited (“CAL”), supply a remuneration notice to CAL and pay any required fees. For details of CAL licences and remuneration notices please contact CAL at Level 11, 66 Goulburn Street, Sydney NSW 2000, Tel: (02) 9394 7600, Fax: (02) 9394 7601 Email: [email protected] Website: www.copyright.com.au For product information and technology assistance, in Australia call 1300 790 853; in New Zealand call 0800 449 725 For permission to use material from this text or product, please email [email protected] National Library of Australia Cataloguing-in-Publication Data ISBN: 9780170457972 A catalogue record for this book is available from the National Library of Australia. Cengage Learning Australia Level 7, 80 Dorcas Street South Melbourne, Victoria Australia 3205 Cengage Learning New Zealand Unit 4B Rosedale Office Park 331 Rosedale Road, Albany, North Shore 0632, NZ For learning solutions, visit cengage.com.au Printed in China by 1010 Printing International Limited. 1 2 3 4 5 6 7 26 25 24 23 22

iii

CONTENTS IN BRIEF

Guide to the text Guide to the online resources Preface About the authors Acknowledgements

viii xi xiii xv xvi

CHAPTER 1

An overview of nutrition

1

CHAPTER 2

Planning a healthy diet

39

CHAPTER 3

Digestion, absorption and transport

66

CHAPTER 4

The carbohydrates: sugars, starches and dietary fibre

97

CHAPTER 5

The lipids: triglycerides, phospholipids and sterols

136

CHAPTER 6

Protein: amino acids

177

CHAPTER 7

Metabolism: transformations and interactions

214

CHAPTER 8

Energy balance and body composition

252

CHAPTER 9

Weight management: overweight, obesity and underweight

283

CHAPTER 10 The water-soluble vitamins: B group vitamins and vitamin C

321

CHAPTER 11 The fat-soluble vitamins: A, D, E and K

366

CHAPTER 12 Water and the major minerals

394

CHAPTER 13 The trace minerals

439

CHAPTER 14 Fitness: physical activity, nutrients and body adaptations

476

CHAPTER 15 Life cycle nutrition: pregnancy and lactation

510

CHAPTER 16 Life cycle nutrition: infancy, childhood and adolescence

546

CHAPTER 17 Life cycle nutrition: adulthood and the later years

583

CHAPTER 18 Diet-related disease

614

CHAPTER 19 Concerns about foods and water

654

Appendix A Cells, hormones and nerves Appendix B Basic chemistry concepts Appendix C Biochemical structures and pathways Appendix D Measures of protein quality Appendix E Nutrition assessment Appendix F Physical activity and energy requirements Appendix G Aids to calculation Answers Glossary Index

689 695 704 721 724 745 748 750 754 776 Beetroot sprouts contain potassium and nitrates which is important for regulating blood pressure

Yellow capsicums are rich in lutein which belongs to the vitamin A family

iv

CONTENTS Pecans are a rich source of fibre, copper, thiamin and zinc

Guide to the text viii Guide to the online resources xi Preface xiii About the authors xv Acknowledgements xvi CHAPTER 1 AN OVERVIEW OF NUTRITION 1 1.1 Food choices 1.2 Nutrients 1.3 The science of nutrition 1.4 Nutrient Reference Values 1.5 Nutrition assessment 1.6 Diet and health CHAPTER ACTIVITIES HIGHLIGHT 1 Nutrition information and misinformation: on the net and in the news

2 5 10 16 21 25 29

32

CHAPTER 2 PLANNING A HEALTHY DIET 39 2.1 Principles and guidelines 2.2 Diet-planning guides 2.3 Food labels CHAPTER ACTIVITIES HIGHLIGHT 2 Vegetarian diets CHAPTER 3 DIGESTION, ABSORPTION AND TRANSPORT 3.1 Digestion 3.2 Absorption 3.3 The circulatory systems 3.4 The health and regulation of the GI tract CHAPTER ACTIVITIES HIGHLIGHT 3 Common digestive problems

40 44 53 58 61

66 67 73 77 80 87 89

CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE

97

4.1 Chemical structure of carbohydrates 98 4.2 The simple carbohydrates 98 4.3 The complex carbohydrates 102 4.4 Digestion and absorption of carbohydrates 104 4.5 Glucose in the body 109 4.6 Health effects and recommended intakes of sugars 115 4.7 Alternative sweeteners 118 4.8 Health effects and recommended intakes of starch and dietary fibre 122 CHAPTER ACTIVITIES 128 HIGHLIGHT 4 Carbs, kilojoules and controversies

131

CHAPTER 5 THE LIPIDS: TRIGLYCERIDES, PHOSPHOLIPIDS AND STEROLS 136 5.1 Chemical structure of fatty acids and triglycerides 137 5.2 Chemical structure of phospholipids and sterols 144 5.3 Digestion, absorption and transport of lipids 146 5.4 Lipids in the body 152 5.5 Health effects and recommended intakes of saturated fats, trans fats and cholesterol 155 5.6 Health effects and recommended intakes of monounsaturated and polyunsaturated fats 157 5.7 From guidelines to groceries 160 CHAPTER ACTIVITIES 166 HIGHLIGHT 5 High-fat foods: friend or foe?

169

Contents

CHAPTER 6 PROTEIN: AMINO ACIDS

177

6.1 Chemical structure of proteins 6.2 Digestion and absorption of protein 6.3 Proteins in the body 6.4 Protein in foods 6.5 Health effects and recommended intakes of protein CHAPTER ACTIVITIES

178 182 183 194 195 204

HIGHLIGHT 6 Nutritional genomics

207

CHAPTER 7 METABOLISM: TRANSFORMATIONS AND INTERACTIONS

214

7.1 Chemical reactions in the body 7.2 Breaking down nutrients for energy 7.3 Feasting and fasting CHAPTER ACTIVITIES

215 219 232 239

HIGHLIGHT 7 Alcohol in the body

241

CHAPTER 8 ENERGY BALANCE AND BODY COMPOSITION

252

CHAPTER 9 WEIGHT MANAGEMENT: OVERWEIGHT, OBESITY AND UNDERWEIGHT

283

9.1 Overweight and obesity 9.2 Causes of overweight and obesity 9.3 Problems of overweight and obesity 9.4 Aggressive treatments for obesity 9.5 Lifestyle strategies 9.6 Underweight CHAPTER ACTIVITIES

284 287 293 296 298 308 312

HIGHLIGHT 9 The latest and greatest weight-loss diet – again

315

CHAPTER 10 THE WATER-SOLUBLE VITAMINS: B GROUP VITAMINS AND VITAMIN C

321

10.1 The vitamins: an overview 10.2 The B group vitamins: as individuals 10.3 The B group vitamins: in concert 10.4 Vitamin C CHAPTER ACTIVITIES

322 325 348 350 357

HIGHLIGHT 10 Vitamin and mineral supplements

360

8.1 Energy balance 253 8.2 Energy in: the kilojoules foods provide 254 8.3 Energy out: the kilojoules the body expends 258 8.4 Body weight, body composition and health 264 8.5 Health risks associated with body weight and body fat 269 CHAPTER ACTIVITIES 272

CHAPTER 11 THE FAT-SOLUBLE VITAMINS: A, D, E AND K

366

11.1 Vitamin A and beta-carotene 11.2 Vitamin D 11.3 Vitamin E 11.4 Vitamin K CHAPTER ACTIVITIES

367 375 380 383 387

HIGHLIGHT 8 Eating disorders

HIGHLIGHT 11 Vitamin D and good health

389

274

Pears are a good source of folate, vitamin C, potassium and copper

v

vi

Contents

Exposing chanterelle mushrooms to sunlight can boost their vitamin D levels

CHAPTER 12 WATER AND THE MAJOR MINERALS

394

12.1 Water and the body fluids 12.2 The minerals: an overview 12.3 Sodium 12.4 Chloride 12.5 Potassium 12.6 Calcium 12.7 Phosphorus 12.8 Magnesium 12.9 Sulphate CHAPTER ACTIVITIES

395 407 408 412 414 416 422 424 426 429

15.1 Nutrition prior to pregnancy 511 15.2 Growth and development during pregnancy 512 15.3 Maternal weight 517 15.4 Nutrition during pregnancy 520 15.5 High-risk pregnancies 526 15.6 Nutrition during lactation 533 CHAPTER ACTIVITIES 539

HIGHLIGHT 12 Osteoporosis and calcium

HIGHLIGHT 15 Foetal alcohol syndrome

541

432

CHAPTER 13 THE TRACE MINERALS

439

CHAPTER 16 LIFE CYCLE NUTRITION: INFANCY, CHILDHOOD AND ADOLESCENCE

546

13.1 The trace minerals: an overview 13.2 Iron 13.3 Zinc 13.4 Iodine 13.5 Selenium 13.6 Copper 13.7 Manganese 13.8 Fluoride 13.9 Chromium 13.10 Molybdenum 13.11 Other trace minerals CHAPTER ACTIVITIES

440 441 451 455 457 458 459 460 462 462 463 466

16.1 Nutrition during infancy 16.2 Nutrition during childhood 16.3 Nutrition during adolescence CHAPTER ACTIVITIES

547 559 571 575

HIGHLIGHT 16 Childhood obesity and the early development of chronic diseases

577

CHAPTER 17 LIFE CYCLE NUTRITION: ADULTHOOD AND THE LATER YEARS

583

HIGHLIGHT 13 Phytochemicals and functional foods

469

CHAPTER 14 FITNESS: PHYSICAL ACTIVITY, NUTRIENTS AND BODY ADAPTATIONS

476

14.1 Fitness 477 14.2 Energy systems and fuels to support activity 484 14.3 Vitamins and minerals to support activity 493 14.4 Fluids and electrolytes to support activity 494 14.5 Diets for physically active people 499 CHAPTER ACTIVITIES 502 HIGHLIGHT 14 Supplements as ergogenic aids

504

CHAPTER 15 LIFE CYCLE NUTRITION: PREGNANCY AND LACTATION

510

17.1 Nutrition and longevity 585 17.2 The ageing process 588 17.3 Energy and nutrient needs of older adults 592 17.4 Nutrition-related concerns of older adults 595 17.5 Food choices and eating habits of older adults 601 CHAPTER ACTIVITIES 605 HIGHLIGHT 17 Nutrient–drug interactions

607

Contents

CHAPTER 18 DIET-RELATED DISEASE 18.1 Nutrition and infectious diseases 18.2 Nutrition and chronic diseases 18.3 Cardiovascular disease 18.4 Hypertension 18.5 Diabetes mellitus 18.6 Cancer 18.7 Recommendations for chronic disease prevention CHAPTER ACTIVITIES HIGHLIGHT 18 Complementary and alternative medicine

614 615 617 620 628 631 637 641 643 645

CHAPTER 19 CONCERNS ABOUT FOODS AND WATER 654 19.1 Food safety and food-borne illnesses 656 19.2 Environmental contaminants 665 19.3 Natural toxins in foods 667

19.4 Pesticides 19.5 Food additives 19.6 Consumer concerns about water CHAPTER ACTIVITIES

668 671 675 679

HIGHLIGHT 19 Food biotechnology

681

Appendix A Cells, hormones and nerves 689 Appendix B Basic chemistry concepts 695 Appendix C Biochemical structures and pathways 704 Appendix D Measures of protein quality 721 Appendix E Nutrition assessment 724 Appendix F Physical activity and energy requirements 745 Appendix G Aids to calculation 748 Answers 750 Glossary 754 Index 776

vii

Kale is an excellent source of vitamin K, but also contains carotenoids which are important in eye health

viii

Guide to the text As you read this text you will find a number of features in every chapter to enhance your study of nutrition and help you understand how the theory is applied in the real world. CHAPTER OPENING FEATURES 1

CHAPTER

1

Connect Nutrition in your life with the essential chapter concepts right from the beginning of each chapter.

AN OVERVIEW OF NUTRITION

Think about your intuitive beliefs related to the nutrition topics covered in the chapter by taking the Common sense test at the start of every chapter. Check your answers in the margins when the topic is discussed. These are explained further in the endof-chapter review.

Nutrition in your life

Believe it or not, you have probably eaten at least 20 000 meals in your life. Without any conscious effort on your part, your body uses the nutrients from those meals to make all its components, fuel all its activities and defend itself against diseases. How successfully your body handles these tasks depends, in part, on your food choices. Nutritious food choices support healthy bodies. PUTTING COMMON SENSE TO THE TEST Circle your answer

Identify the key concepts that the chapter will cover with the Learning objectives at the start of each chapter.

T

F

For good health, it is best to avoid all processed foods.

T

F

Fat has twice the number of kilojoules as carbohydrates or protein.

T

F

All published research should be treated with some level of critical appraisal.

T

F

A Recommended Dietary Intake for a nutrient is the amount that everyone needs to consume each day.

T

F

Changing our diet will do little to reduce the risk of many chronic diseases.

LEARNING OBJECTIVES 1.1 1.2

1.3

Describe how various factors influence personal food choices. Name six major classes of nutrients and identify which are organic and which yield energy. Explain the scientific method and how scientists use various types of research studies and methods to acquire nutritional information.

1.4

1.5

1.6 1.7

Define the four categories of the Nutrient Reference Values (NRVs) and explain their purpose. Explain how the four nutrition assessment methods for an individual are used to detect energy and nutrient deficiencies and Chapter 1: An overview of nutrition excesses. Identify several risk factors for chronic disease and explain their relationship. Recognise misinformation and describe how to identify reliable nutrition information.

9

harm it does far exceeds the problems of excess body fat. (Highlight 7 describes the effects of Onions contain antioxidants and compounds that fight inflammation, alcohol on health and nutrition.) decrease triglycerides and reduce cholesterol levels

Other roles of energy-yielding nutrients

FEATURES WITHIN CHAPTERS Chapter 2: Planning a healthy diet

hem described as refined, enriched e making of grain products, and fined foods may have lost many had some nutrients (generally s may be rich in fibre and all the upport good health and should

tified foods on the market. A the added nutrients may not have when selecting breakfast cereals nerals as, while these may appear provide the full spectrum of might provide. other breads. However, due to ew Zealand (FSANZ), Australian d to all bread flours, except for ortification of bread flour was acid is important in the healthy f neural tube defects. In New o 50 per cent of packaged sliced d for bread making required to be

51

Practise common nutrition tasks such as comparing Grain-enrichmentdensity or calculating your energy nutrient nutrients include: • iron requirements by working through the How to boxes • thiamine • riboflavin throughout the book. • niacin • folate.

AUSTRALIAN DIETARY GUIDELINES 2013 ---------------

Connect key Australian Dietary Guidelines to your understanding of the chapter.

Enjoy a wide variety of nutritious foods every day, including milk, plenty of fruits and vegetables of 2 differentUnderstanding Nutrition types and colours and legumes/beans.

In general, a chronic disease progresses slowly or with little change and lasts a long time. By comparison, an acute disease develops quickly, produces sharp symptoms and runs a short course. • chronos = time • acute = sharp

r are: ground endosperm that is usually enriched with nutrients iteness; sometimes called white flour. ur made from the endosperm of the wheat kernel. any flour made from the entire wheat kernel.

n white flour and white wheat is noteworthy. Typically, white flour (as defined above). Most flour – whether refined, white, ade from red wheat. Wholegrain products made from red own and full-flavoured.

uest Photographic, Inc.

s the endosperm; that is why they are so nutritious. Refined ded back, they are not as nutritious as wholegrain

In addition to providing energy, carbohydrates, fats and proteins provide the raw materials for building the body’s tissues and regulating its many activities. In fact, protein’s role as a fuel source is relatively minor compared with the other two nutrients and its other roles. Proteins are found in structures such as the muscles and skin and help to regulate activities such as digestion and energy metabolism. BK-CLA-WHITNEY_5E-210367-Chp01 copy.indd 1

HOW TO:

CALCULATE THE ENERGY AVAILABLE FROM FOODS

Practise calculating the energy available from foods. 1. To calculate the energy available from a food, multiply the number of grams of carbohydrate, protein and fat by 17, 17 and 37, respectively. Then add the results together – e.g. 1 slice of bread with 1 tablespoon of peanut butter on it contains 16 grams carbohydrate, 7 grams protein and 9 grams fat.

16 g carbohydrate × 17 kJ/g = 272 kJ 7 g protein × 17 kJ/g = 119 kJ 9 g fat × 37 kJ/g = 333 kJ Total = 724 kJ

From the information you calculated in step 1, you can determine the percentage of kilojoules each of the energy nutrients contributes to the total. 2. To determine the percentage of kilojoules from fat, for example, divide the 333 fat kilojoules by the total 724 kilojoules. 3. Then multiply by 100 to get the percentage.

333 fat kJ ÷ 724 total kJ = 0.46 0.46 × 100 = 46%

Dietary recommendations that urge people to limit fat intake to 20 to 35 per cent of kilojoules refer to the day’s total energy intake, not to individual foods. Still, if the proportion of fat in each food choice throughout a day exceeds 35 per cent of kilojoules, then the day’s total surely will, too. Knowing that this snack provides 46 per cent of its kilojoules from fat alerts a person to the need to make lower-fat selections at other times that day.

Welcome to the world of nutrition. Although you may not always have been aware of it, nutrition has played a significant role in your life. And it will continue to affect you in major ways, depending on the foods you select. Every day, several times a day, you make food choices that influence your body’s health for better or worse. Each day’s choices may benefit or harm your health only a little, but when Vitamins are organic but they do not provide energy. Instead, they facilitate the release these choices are repeated over years and decades, the rewards or consequences become major. of energy from carbohydrate, fat and protein and participate in numerous other activities That being the case, paying close attention to good eating habits now can bring health benefits throughout the body. later. Conversely, carelessness about food choices can contribute to many chronic diseases Each of the 13 different vitamins has its own special role to play. One vitamin enables prevalent in later life, including heart disease and cancer. Of course, some people will become the eyes to see in dim light, another helps produce functional red blood cells, and still another ill or die young no matter what choices they make, and others will live long lives despite helps make the sex hormones – among other things. When you cut yourself, one vitamin making poor choices. For most of us, however, the food choices we make each and every day helps stop the bleeding and another helps repair the skin. Vitamins busily help replace old red will benefit or impair our health in proportion to the wisdom of those choices. blood cells and the lining of the digestive tract. Almost every action in the body requires the Although most people realise that their food habits affect their health, they often choose assistance of vitamins. foods for other reasons. After all, foods bring to the table a variety of pleasures, traditions and Vitamins can function only if they are intact, but because they are complex organic associations as well as nourishment. The challenge, then, is to combine favourite foods and molecules, they are vulnerable to destruction by heat, light and chemical agents. This is why fun times with a nutritionally balanced diet. the body handles them carefully, and why nutrition-wise cooks do, too. The strategies of cooking vegetables at moderate temperatures for short times and using small amounts of water help to preserve the vitamins.

Vitamins Extend your learning with the additional information notes highlighting interesting or important information about the topic being discussed.

1.1 Food choices

22/03/22 6:11 PM

People decide what to eat, when to eat and even whether to eat in highly personal ways, often based on behavioural or social motives rather than on an awareness of nutrition’s importance to health.

The water-soluble vitamins are vitamin C and the eight B vitamins: thiamin, riboflavin, niacin, vitamins B6 and B12, folate, biotin and pantothenic acid. The fat-soluble vitamins are vitamins A, D, E and K. The water-soluble vitamins are the subject of Chapter 10, and the fat-soluble vitamins are discussed in Chapter 11.

Guide to the text

FEATURES WITHIN CHAPTERS

Chapter 1: An overview of nutrition

5

ultra-processed foods. Ultra-processed foods no longer resemble whole foods. They are made from substances that are typically used in food preparation but not consumed as foods themselves (e.g. oils, fats, flours, refined starches and sugars). These substances undergo further processing by adding little, if any, processed foods, salt and other preservatives, and additives such as flavours and colours. Examples of ultra-processed foods include soft drinks, corn chips, confectionery, chicken nuggets and pastries. Notably, these foods cannot be made in a home kitchen using common grocery ingredients. Dominating the global foods market, ultra-processed foods tend to be attractive, tasty and cheap – as well as high in fat and sugar. Consumers who want to make healthy food choices will select fewer ultra-processed foods and Chapter 1: 1: An An overview overview of of nutrition nutrition Chapter more whole foods and minimally processed foods.4

27 5

CURRENT RESEARCH IN NUTRITION The perils of highly processed foods

Explore relevant and up-to-date nutrition research in the Current research in nutrition boxes.

The review looked at the disease linksover-represented from 304 meta-analyses Ultra-processed foods are diet the and typeschronic of foods that are in the listand of systematic reviews in the last 63 Type 2 diabetes, and obesity, discretionary food published choices. Such foods areyears. not an essential part ofoverweight a nutritious diet. Now cancer cardiovascular disease together accounted for mostmay of disease links nutritional researchers linking these foods as athose major driver of the overweight and obesity, A personand selects foods forare a variety of reasons. Whatever reasons be, chronic food choices found. type 2 while also contributing to non-communicable heart disease, influence health. Individual food selections neither makediseases, nor break such a diet’sas healthfulness, but the As for dietary patterns, showed that plant-based more protective and certain cancers. diabetes balance of foods selected overthe timefindings can make an important difference tofoods health.were For this reason, against the risk developing chronic disease animal-based foods. Among A recent systematic review and meta-analysis looked at with the links between ultra-processed people are wise toof think ‘nutrition’ when making theircompared food choices. 5 plant grain-based foods seemed to have a small over fruits and vegetables. So From 21 cross-sectional andedge 19 prospective studies, increasing foodsfoods, and chronic disease. much for the anti-grain sentimentfoods that iswas popular moment! consumption of ultra-processed linkedattothe a greater risk of overweight or obesity; For animal-based dairy products overall were considered on health, metabolic syndrome;foods, depression; cardiometabolic diseases, suchneutral as heart diseaseand or fish was considered protective. Red and processed meats weremortality. linked to a higher disease diabetes; frailty; irritable bowel syndrome; cancer and all-cause risk.Most For tea-lovers, this popular drink thefoods protective of the foodthe weresearch eateat is processed some degree. But isbeing only the considered Biologically speaking, people toconfirmed receive to nourishment. Do youitasever think ofmost yourself as a against disease risk. of Onthat thewe other end aim of the no-one’s surprise, soft drinks had to be ultra-processed should to spectrum, eat molecules, less of.toEating food as close to its natural biological being made carefully arranged atoms, cells , tissues and organs? Are few redeeming health benefits. state as of possible, making food from original ingredients andsitchoosing wide variety of you aware the activity going on within your body even as you still? Theaatoms, molecules The plant-based from thisare major review are close to athough carbonthe copy of existing dietary mostly foods themove keys to eating a healthy diet. and cells offindings your body continually and change, even structures of your tissues Chapter 1: An overview of nutrition guidelines that have changed little over decades. Eat more plant-based foods than animal foods, choose whole grains over refined grains, limit red and processed meat and choose Chapter 1: An overview of nutrition other beverages in preference toreasons. soft drink. Suchthose recommendations maychoices not get media A person selects foods for a variety of Whatever reasons may be, food or help sell books numbersneither like the latest diet, buthealthfulness, they are thebut cornerstone 30attention Understanding Nutrition influence health. Individual foodinselections make nor fad break a diet’s the of long-term health. balance of foods selected over time can make an important difference to health. For this reason, REVIEW IT

Evaluate how current research in the field informs our practical health and food choices in the Applications of nutritional research boxes in every chapter.

TABLE 1.8believe Factors contributing to deaths andcut disease burden infoods? Australia ultra-processed foods . Ultra-processed foods no longer resemble whole foods. are Do you the key to good health is to just out processed The termThey ‘processed made from are typically usedwe inneed food to preparation consumed food’ maysubstances seemRISK like FACTOR athat dietary demon that avoid, but but it is not aOF concept that as has little a foods PERCENTAGE TOTAL DALY themselves fats, flours, refinedfood starches and sugars). These substances meaning (e.g. and isoils, unhelpful in informing choices. Almost everything you eat undergo is processed Tobacco 9.0 to an processing extent. Even food is form of food processing. A much helpful concept further bycooking adding little, if aany, processed foods, salt and othermore preservatives, and Alcohol 5.1 is to divide into categories basedExamples on their degree of processing. So, include on the positive side additives suchfood as flavours and colours. of ultra-processed foods soft drinks, think more of food that has beennuggets minimally processed and is stillthese close to itscannot naturalbe state in corn chips, confectionery, chicken and pastries. Notably, foods made Physical inactivity 5.0 appearance and nutritional quality. Here it is all about fruits vegetables, fruits, wholegrains, inHigh a home bodykitchen mass using common grocery ingredients. Dominating the 5.5global foods market, nuts, milk, fresh meats and And tasty against that, we have the foods weinshould besugar. most ultra-processed foods tend tolegumes. be attractive, and cheap – as well as high fat and High blood pressure 4.9 concerned about – ultra-processed Consumers who want to make healthyfoods. food choices will select fewer ultra-processed foods and are industrial formulations substances that contain High Ultra-processed plasmafoods glucose more whole andfoods minimally processed foods.4 of food-derived 2.7 little if any whole food. Ultra-processed foods often include ingredients not commonly used High cholesterol 2.4 in home cooking such as flavourings, colourings, emulsifiers and other additives. A key CURRENT RESEARCH IN NUTRITION Diet low in fruit 2.0 feature of ultra-processed foods is that they are usually appetising and pleasing to the taste Diet low in vegetables 1.1 buds, convenient, sold in large packages and highly marketed. The perils of highly processed foods Ultra-processed foods are health the types that are over-represented in ‘processed the list of Do low you believe key to good is to of justfoods cut out processed foods? Diet in wholethe grains 1.1 The term discretionary food choices. Such foods are not an essential part of a nutritious diet. Now a food’ may seem like a dietary demon that we need to avoid, but it is a concept that has little DALY: Disability-Adjusted Life Year. The DALY is a measure of overall disease burden, expressed as the nutritional researchers are linking these foods as a major driver of overweight and obesity, meaning andlost is unhelpful in informing food choices. number of years due to ill-health, disability or early death.Almost everything you eat is processed type 2 while also contributing to food non-communicable such as heart to an extent. Even cooking is a form of fooddiseases, processing. A much moredisease, helpful concept Australian Institute of Health and Welfare, Australian Burden of Disease Study: impact and causes of illness and death in diabetes and certain cancers. based on their degree of processing. is to divide food into categories So, on the positive side CC-BY 3.0 Licence. (https://www.aihw.gov.au/copyright). https://www.aihw.gov.au/reports/burden-ofAustralia 2011, (2016). A more recentofsystematic andminimally meta-analysis lookedand at the linksclose between disease/abds-impact-and-causes-of-illness-death-2011/contents/highlights think food thatreview has been processed is still to itsultra-processed natural state in 5 From 21 cross-sectional and 19 vegetables, prospective fruits, studies, increasing foods and chronic disease. quality. appearance and nutritional Here it is all about fruits wholegrains, consumption of meats ultra-processed foods was linkedthat, to a we greater overweight or be obesity; nuts, milk, fresh legumes. And against have risk the of foods we should most APPLICATIONS OF and NUTRITIONAL RESEARCH metabolic about syndrome; depression; foods. cardiometabolic diseases, such as heart disease or concerned – ultra-processed diabetes; frailty; irritable cancer and mortality. The key dietary patterns ofsyndrome; long-term health Ultra-processed foodsbowel are industrial formulations ofall-cause food-derived substances that contain the we eat is processed to some degree. But it is only considered Diet plays bigfood part inUltra-processed health. As the typical Western diet moved tothe more overly refined littleMost if anyofawhole food. foods often include ingredients notfoods commonly used to home be ultra-processed we should aim to type eat less of. Eating foodother as close to itsAnatural and energy dense foods, rates of obesity and 2 emulsifiers diabetes mirrored this change. major in cooking suchthat as flavourings, colourings, and additives. A key state asofpossible, food is from original and choosing a health widetovariety of scientific review hasmaking taken things back basics to reinforce where the best gains are feature ultra-processed foods thatto they areingredients usually appetising and pleasing the taste 15 mostly plant-based foods are the keys to eating a healthy diet. to be found with diet. buds, convenient, sold in large packages and highly marketed.

1.2 Nutrients

CHAPTER ACTIVITIES people are wise to think ‘nutrition’ when making their food choices. CHAPTER ACTIVITIES Other risk factors, such as genetics, sex and age, also play important roles in the

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REVIEW IT

Consolidate your learning with the Review it summary paragraph at the end of each A-head section reviewing key concepts for that Learning Objective.

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PUTTING SENSE TO THE TEST: ANSWERS 9 A deficiency caused by an inadequate dietary intake 7 An EAR forCOMMON a nutrient development of chronicrepresents: diseases, but they cannot be changed. Health recommendations is a(n): average amount aavoid nutrient that a group 1 a Forthe good health, it is bestoftoof all factors processed foods. 4 A Recommended Dietary Intake forfocus a nutrient is the acknowledge the influence such on theofdevelopment of disease, but they must PUTTING SENSE TO THE TEST: ANSWERS amount a overt deficiency healthyCOMMON people consume FALSE that everyone consume on the factors that are changeable. For the two out of three Australians who doneeds not to smoke or each day. Biologically speaking, people eat tomany receive Dobyoucovert ever deficiency think of yourself as a b thefoods lowest amount a nutrient that willnourishment. maintain are processed toof a the degree andall of these foods are influence 1 Most For good health, it is best to avoid processed foods. 4 FALSE A Recommended Dietary Intake for a nutrient is the drink alcohol excessively, one choice that can long-term health prospects more c RDI primary deficiency a specified of adequacy biological being of ‘ultra-processed’ carefully arranged cells , tissues organs? Areof 98 healthy for us. Itmade iscriterion more the foods that atoms, we should molecules, An is that set ateveryone the leveland ofneeds meeting the needs perday. cent of the FALSE amount to consume each thanc any is diet. dyousecondary deficiency. the highest amount going of a nutrient that appears limit inother our diet. population is targeting. Most people require less than this, but a you aware of the activity on many within your sit itstill? The atoms, molecules Most foods are processed to a degree and of these foodsbody are even as FALSE small number require more. safe for most number healthy of people 2 cells Fat has twice kilojoules as carbohydrates 10 though Behaviours such asofsmoking, physical and offor your body continually move and of your tissues healthy us. Itthe is more the ‘ultra-processed’ foods that wechange, shouldor even An RDI isthe set atstructures the level meeting thedietary needs ofhabits, 98 per cent of the d protein. the daily nutrient intake level estimated to meet 5 Changing diet willMost do little torequire reduce risk ofbut many activity alcohol consumption that influence the limit in ourTRUE diet. populationand itour is targeting. people lessthe than this, a the 37 requirements of half the individuals in chronic diseases. development of FALSE disease are known as: small number require more. kJ/g compared with 17 forhealthy carbohydrate and protein. 2 Fat Fathas has twice the number ofkJ/g kilojoules as carbohydrates or a particular life stage and gender group. plays large role in causing manytoofreduce the chronic are a riskafactors TRUEresearch should be treated with some level 5 Diet Changing our diet will do little thediseases risk of we many protein. 3 All published faced with today, such as cancer, heart disease, stroke and diabetes. 8 Historical information, physical examinations, FALSE chronic diseases. b chronic causes TRUE of appraisal. Fatcritical has 37 kJ/g compared with 17 kJ/g for carbohydrate and protein. laboratory testsstudy andisanthropometric measures are: cDiet plays preventive agents a large role in causing many of the chronic diseases we are researchresearch perfect, anytreated interpretation of a study 3 No Allone published shouldsobe with some level faceddisease with today,descriptors. such as cancer, heart disease, stroke and diabetes. be done within thein context of the study design limitations. d a should used diet planning of techniques critical appraisal. BK-CLA-WHITNEY_5E-210367-Chp01 copy.indd 27 TRUE BK-CLA-WHITNEY_5E-210367-Chp01 copy.indd b Nosteps used in5 the scientific method one research study is perfect, so any interpretation of a study c should approaches used disease be done within the in context of theprevention study design limitations. NUTRITION d methodsPORTFOLIO used in a nutrition assessment.

1.2 Nutrients

END-OF-CHAPTER FEATURES

At the end of each chapter you’ll find several tools to help you review, practise and extend your knowledge of the key learning outcomes. • Reflect on your own personal nutritional choices in the Nutrition portfolio.

• Review the major chapter concepts in preparation for exams by completing the Study questions.

• Master the common Nutrition calculations introduced in the How to chapter features.

• Expand your knowledge by exploring the online resources listed in Nutrition on the net.

Each chapter in this book ends with simple ‘Nutrition REVIEW QUESTIONS NUTRITION PORTFOLIO portfolio’ activities that invite you to review key messages consider whether your personal choices are meeting 1and Give several (and examples) why‘Nutrition people Each chapter in reasons this book ends with simple the dietarythe goals inyou the By keeping make foodintroduced choices that they do. (Section 1.1)a portfolio’ activities that invite totext. review key messages journal of these ‘Nutrition you can and consider whether yourportfolio’ personalassignments, choices are meeting 2examine What how is a nutrient? Name the six classes of nutrients yourintroduced knowledgeinand change the dietary goals thebehaviours text. By keeping a as found in foods. What is an essential nutrient? you progress in your study of nutrition. journal of these ‘Nutrition portfolio’ assignments, you can (Section 1.2) Your food choices play a key role in keepingchange you as examine how your knowledge and behaviours and reducing your risk of chronic diseases. 3healthy Which nutrients are inorganic and which are you progress in your study of nutrition. organic? significance of keeping that distinction. Your foodDiscuss choicesthe play a key role in you (Section 1.2) healthy and reducing your risk of chronic diseases. STUDY QUESTIONS

4Multiple Whichchoice nutrients yield energy and how much energy questions STUDY QUESTIONS do they yield per gram? energy measured? Answers can be found at theHow backisof the book. 1.2) eat the foods that are influenced by the 1 (Section When people

Multiple choice questions

companionship of friends and family in aenergy group, their canthe be found at for thecalculating back of thethe book. 5Answers Describe process choices are influenced by: that from foods. 1.2) 1 available When people eat the (Section foods are influenced by the acompanionship habit of friends and family in a group, their 6 What is the science of nutrition? Describe the types bchoices ethnic or tradition areheritage influenced by: of research studies and methods used in acquiring ca personal preference habitinformation. nutrition (Section 1.3) db social interactions. ethnic heritage or tradition 7 What are the strengths and weaknesses of the 2 Nutrients the preference human body must obtain from the diet c personal different types of research designs? (Section 1.3) because they cannot be made internally are called: d social interactions. essential 2 aNutrients the nutrients human body must obtain from the diet NUTRITION CALCULATIONS Note:they The total should addinternally up to 100%, 99% or bbecause conditionally essential nutrients cannot be made arebut called: 101% due to rounding is also acceptable. non-essential nutrients Manycachapters endnutrients with problems to give you practice in essential Calculate howessential many ofcalculations. the 460 kilojoules provided organic nutrients. doingdcbsimple nutrition-related Although the conditionally nutrients by a 150-millilitre glass of white wine come from situations are hypothetical, the numbers are real, and 3 The nutrients are: c inorganic non-essential nutrients alcohol, if the wine 0.4 grams protein calculating the answers (seecontains the answers sectionofat the organic nutrients. ad carbohydrates, proteins and fats andbook) 0.4 grams of carbohydrate. (NOTE:lesson. The back of this provides a valuable nutrition minerals 3 bThe vitamins inorganicand nutrients are: kilojoules from you alcohol.) Once you remaining have mastered thesederive examples, will be ca minerals and water carbohydrates, and 0.4 g protein = ____ kJfats proteinBe sure to prepared to examine yourproteins own food choices. db water andand proteins. vitamins minerals 0.4 g carbohydrate = ____ kJ carbohydrate show your calculations for each problem. c minerals and water= ____ kJ alcohol 1 Calculate the energy provided by a food’s energyd Total water and proteins.= ____ % nutrient contents. A cup of fried rice contains 5 grams protein, 30 grams carbohydrate and 11 grams fat.

• For the foods and snacks you eat over a typical day, identify the factors that most influence your choices. List the chronic disease risk factors and conditions 8•• What arefoods the NRV? To whom they apply? Howday, are For the and snacks youdo eat over a typical (see Table 1.8) that description, you members of your family they used? Infactors your identify the categories identify the thatormost influence your choices. have. NRV indicate how they related. (Section 1.4) • of List theand chronic disease risk are factors and conditions • Describe you can make to family improve (see Tablelifestyle 1.8) thatchanges you or members of your 9 What judgement factors are involved in setting the your have.chances of enjoying good health. energy and nutrient recommendations? (Section 1.4) • Describe lifestyle changes you can make to improve 10 What happens when people get either too little or your chances of enjoying good health. too much energy or nutrients? Define malnutrition, undernutrition and overnutrition. Describe the four methods used to detect energy and nutrient 4 The energy-yielding nutrients are: deficiencies and excesses. (Section 1.5) a fats, minerals and water 11 methods proteins are used in nutrition bThe minerals, and vitamins 4 What energy-yielding nutrients are: surveys? What kinds of information fats can and these surveys provide? ca carbohydrates, fats, minerals and watervitamins (Section 1.6) db carbohydrates, fatsand andvitamins proteins. minerals, proteins 12 factorsfats and their relations to disease 5 Describe Studies ofrisk populations that reveal correlations c carbohydrates, and vitamins (Section 1.6) between dietary habits incidence are d carbohydrates, fatsand anddisease proteins. termed: 5 Describe Studies of populations that reveal correlations 13 the leading causes of death and their Chapter 1: An overview of nutrition 31 abetween clinical trials dietary habits disease incidence are1.6) relationships to diet andand lifestyle factors. (Section btermed: laboratory studies ca randomised clinical trialstrials db epidemiological studies. laboratory studies 6

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NUTRITION ON THE NET

Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you BK-CLA-WHITNEY_5E-210367-Chp01 copy.indd 29 eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New BK-CLA-WHITNEY_5E-210367-Chp01 copy.indd 29 Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx BK-CLA-WHITNEY_5E-210367-Chp01 copy.indd 30 • Search for ‘nutrition’ at the National Health and Medical Research Council site: http://www.nhmrc. gov.au • Review the Nutrient Reference Values: http://www. nrv.gov.au • Review nutrition recommendations from the Food and Agriculture Organization of the United Nations and

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•

•

How many grams of alcohol does this represent? An intrials which the researchers know who____ c experiment randomised g receiving thekilojoules treatment but the subjects do not is d alcohol epidemiological studies. ais How many does rice provide from known as: these energy To your nutrition to identify bogus An apply experiment innutrients? whichknowledge the researchers know who ______________ = ____ kJ protein consider an advertisement for a new aclaims, single blind is receiving the treatment but the subjects do not is ______________ = ____ kJ carbohydrate that claims to contain b‘superfood double control supplement’ known as: protein ______________ = ____ kJ fat protein and 50 kilojoules per dose. Is this c20 double blind a grams singleofblind Total ____ = ____ kJ ____ = ____ kJ Why or why not? dpossible? control. b placebo double control b What percentage of the energy in the fried c double blind rice comes from each of the energy-yielding d placebo control. nutrients? ______________ = ____ % kJ from protein ______________ = ____ % kJ from carbohydrate ______________ = ____ % kJ from fat Total = ____ % the World Health Organization: http://www.fao.org and http://www.who.org 22/03/22 Read about the Selected Highlights from the 2017–18 National Health Survey https://www.abs.gov.au/ statistics/health/health-conditions-and-risks/ 22/03/22 national-health-survey-first-results/2017-18 Read about food and nutrition monitoring in New Zealand by searching ‘nutrition survey’ at http://www. health.govt.nz Visit the food and nutrition centre at the Mayo Clinic: http://www.mayohealth.org

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Understanding Nutrition

HIGHLIGHTS

32

Every chapter is followed by a highlight that provides readers with an in-depth look at a current, and often controversial, topic that relates to its companion chapter • Develop your understanding of these key topics by responding to the critical thinking questions. Chapter 1: An overview of nutrition

37

• Research these thought-provoking topics further by exploring the weblinks listed in Nutrition on the net. pollution. Countries have different laws regarding sales of drugs, dietary supplements and other health products, but applying these laws to the internet marketplace is almost impossible. Even if illegal activities could be defined and identified, finding the person responsible for a particular website is not always possible. Websites can open and close in a blink of a cursor. Now more than ever, consumers

must heed the caution, ‘Buyer beware’. In summary, when you hear nutrition news, consider its source. Ask yourself these two questions: Is the person providing the information qualified to speak on nutrition? Is the information based on valid scientific research? If not, find a better source. After all, your health depends on it.

HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1

How would you judge the accuracy or validity of nutrition information?

2

You have just received a forwarded email from a friend warning that the artificial sweetener aspartame is a TOXIN that causes muscle spasms, leg numbness, stomach cramps, vertigo, dizziness, headaches, tinnitus, joint pain, depression, anxiety, slurred speech, blurred vision, and memory loss. It goes on

to say that this DEADLY POISON causes blindness, multiple sclerosis, brain tumours, and cancer! The message alleges that aspartame remains on the market because of a conspiracy between FSANZ and the manufacturer to keep these dangers hidden from the public. How can you determine whether these claims are legitimate warnings or an irresponsible hoax?

NUTRITION ON THE NET •

•

•

•

Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand at http://www.foodstandards. gov.au/science/monitoringnutrients/pages/default. aspx Find an accredited practising dietitian in your area by consulting the Dietitians Australia website; also find out which nutrition and dietetics courses are accredited by the association: https:// dietitiansaustralia.org.au Learn about the Registered Nutritionist program at the Nutrition Society of Australia: http://www.nsa. asn.au Read about the professional registration of nutritionists in New Zealand: http://www. nutritionsociety.ac.nz/registration

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For foods commonly eaten in New Zealand, you can analyse their nutrient content from the database maintained by Plant and Food New Zealand: http://www.foodcomposition.co.nz Learn more about quackery from Stephen Barrett’s Quackwatch: http://www.quackwatch.org Visit the National Council against Health Fraud: http://www.ncahf.org Check out health-related hoaxes and urban legends: http://www.urbanlegends.about.com Find reliable research articles: https://pubmed.ncbi. nlm.nih.gov

Understanding Nutrition

HIGHLIGHT

1

1.7 NUTRITION INFORMATION AND MISINFORMATION: ON THE NET AND IN THE NEWS

Do keto diets really help with weight loss, or is it better to practise intermittent fasting? What is plant-based eating all about? Will nutrigenomics have the answers to all our health questions? Is the microbiome helpful or harmful? Food and nutrition trends such as these have always swirled around the world of nutrition. Some arise out of the latest research and have the backing of scientific evidence. They have staying power, whereas those based on nonsense fade away as soon as the next fanciful trend 38 Understanding Nutrition chapters present the catches our attention. Upcoming scientific findings of these and other trending topics, but it is most important that readers be able to spot a trend and determine its validity. How can people distinguish valid nutrition information from misinformation? One excellent approach is to notice who is providing the information. The ‘who’ behind the information is not always evident, though, especially in the world of electronic media. Keep in mind that people CHAPTER create apps, blogs, and websites on the internet, just as 1 L. Hwang and co-authors, New insight into human sweet taste: people write books and report the news. In all cases, A genome-wide association study of the perception and intake of consumers need toAmerican determine whether person sweet substances, Journal of Clinicalthe Nutrition 109is (2019): qualified to provide nutrition information. 1724–1737. 2 This C. Smith and co-authors, changes in the intakes of foods among highlight begins Secular by examining unique New Zealand adults fromproblems 1997 to 2008/09, Publicon Health potential as well as the of relying theNutrition internet (2015): doi: 10.1017/S1368980015000890 and the media for nutrition information. It continues 3 S. L. Johnson, Developmental and environmental influences on withyoung a discussion of how preferences to identify reliable nutrition children’s vegetable and consumption, Advances in information applies to all resources, including the Nutrition 7that (2016): 220S–213S. 4 L. Schnabel and news. co-authors, Association between ultraprocessed internet and the (The Glossary defines related food consumption and risk of mortality among middle-aged adults in terms.) France, JAMA Internal Medicine 179 (2019): 490–498. This discussion recognises that identifying nutrition 5 M. M. Lane and co-authors, Ultraprocessed food and chronic misinformation requires more than simply gathering noncommunicable diseases: A systematic review and meta analysis accurate information, although is 9a(2020): good start; it of 43 observational studies, Obesity that Reviews doi: 10.1111/ obr.13146 requires critical thinking. Critical thinking allows a person 6 B. gathered Katan and co-authors, Which whoM. has information to:are the greatest recent discoveries and the greatest future challenges in nutrition? European Journal of • understand the connections between concepts Clinical Nutrition 63 (2009): 2–10. • identify and evaluate the pros and cons of an argument 7 J. P. A. Ioannidis, The challenge of reforming nutritional • detect inconsistencies andof errors epidemiologic research, Journal the American Medical Association 320 (2018): 969–970. • solve problems 8 J. P. A. Ioannidis and J. F. Trepanowski, Disclosures in nutrition • identify the relevance of information. research: Why it is different, Journal of the American Medical To that end, the questions at the end of the highlights Association 319 (2018): 547–548. that Australian follow all chapters Department are intended to help develop 9 Government of Health and Ageing, National critical thinking skills. Health and Medical Research Council (Australia), Ministry of Health

REFERENCES

Nutrition on the net Got a question? The internet has an answer. The internet offers endless opportunities to obtain highquality information, but it also delivers an abundance of incomplete, misleading or inaccurate information. Simply put, anyone can publish anything. Determining whether information is balanced, accurate, and credible has become increasing challenging in recent years.1 With hundreds of millions of websites, a person searching for valid nutrition information can be overwhelmed with uncertainty. When using the internet, keep in mind that the quality of health-related information available covers a broad range. You must evaluate websites for their accuracy, just like every other source. The ‘How to’ box that follows provides tips for determining whether a website is reliable. One of the most trustworthy sites used by scientists and others is the US National Library of Medicine’s (New Zealand), Nutrient Reference Values to for over Australia New PubMed, which provides free access 30 and million Zealand, Canberra: Commonwealth of Australia and New Zealandthe research papers published in scientific journals around Government (2006). world. Many abstracts provide links to websites where full 10 Department of Community Services and Health, National dietary articles are available. Figure H1.1 introduces this valuable survey of adults, 1983. No. 2. Nutrient intakes, Canberra: AGPS resource. (1987); Department of Community Services and Health, National schoolchildren (10–15warning years): 1985. Nutrient Ifdietary you survey have of received an email of No. the2.health intakes, Canberra: AGPS Australian Bureauplastic of Statistics, dangers associated with(1989); reusing or freezing water National Nutrition Survey: Nutrient intakes and physical measurements, bottles, you have been a victim of urban scarelore. When Australia, 1995, ABS Catalogue Number 4805.0, Canberra: ABS nutrition arrives in unsolicited emails, (1998);information Australian Bureau of Statistics, National health survey:be first suspicious if: results, 2017–2018, ABS Catalogue Number 4364.0.55.001, Canberra: ABS person (2018). sending it to you did not write it and • the 11 you Newcannot Zealand Ministry of Health, available at determine who Nutrition did or ifSurvey, that person is a http://www.health.govt.nz/nz-health-statistics/national-collectionsnutrition expert and-surveys/surveys/current-recent-surveys/nutrition-survey • the toNew everyone know’ appears 12 Newphrase Zealand‘Forward Ministry of this Health, Zealandyou Nutrition Survey, • the phrase ‘This is not a hoax’ appears; chances are available at https://www.health.govt.nz/nz-health-statistics/nationalcollections-and-surveys/surveys/new-zealand-health-survey that it is 13 Newnews Zealand of Health, webnever tool, available • the is Ministry sensational andMortality you have heard at about https://www.health.govt.nz/publication/mortality-web-tool it from legitimate sources 14 Australian Institute of Health and Welfare, Australian Burden of • the language is emphatic and the text is sprinkled with Disease Study: Impact and causes of illness and death in Australia 2011 capitalised words and exclamation marks (2016). 15 A. Fardet and Y. Boirie, Associations between food • no references are given or, if present, areand of beverage groups and major diet-related chronic diseases: An exhaustive review questionable validity when examined. of pooled/meta-analyses and systematic reviews, Nutrition Reviews 72 (2014): 741–762.

HIGHLIGHT 1 2

S. Rowe and N. Alexander, On post-truth, fake news, and trust, Nutrition Today 52 (2017): 179–182. C. Korownyk and co-authors, Televised medical talk shows – What they recommend and the evidence to support their recommendations: A prospective observational study, British Medical Journal 349 (2014): doi 10.1136/bmj.g7346

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M. Adamski and co-authors, Are doctors nutritionists? What is the role of doctors in providing nutrition advice? Nutrition Bulletin 43 (2018): 147–152.

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Guide to the online resources FOR THE INSTRUCTOR Cengage is pleased to provide you with a selection of resources that will help you to prepare your lectures and assessments, when you choose this textbook for your course. Log in or request an account to access instructor resources at cengage.com.au/instructors for Australia or cengage.co.nz/instructors for New Zealand. MINDTAP Premium online teaching and learning tools are available on the MindTap platform – the personalised eLearning solution.

MindTap is a flexible and easy-to-use platform that helps build student confidence and gives you a clear picture of their progress. We partner with you to ease the transition to digital – we’re with you every step of the way. The Cengage Mobile App puts your course directly into students’ hands with course materials available on their smartphone or tablet. Students can read on the go, complete practice quizzes or participate in interactive real-time activities.

MindTap for Whitney’s Understanding Nutrition is full of innovative resources to support critical thinking and help your students move from memorisation to mastery! Includes: • Whitney’s Understanding Nutrition eBook • Interactive nutrition calculations, Common sense test, Concept checks, Case activities, Quizzes and more

MindTap is a premium purchasable eLearning tool. Contact your Cengage learning consultant to find out how MindTap can transform your course.

INSTRUCTOR’S MANUAL The Instructor’s Manual includes: • Learning objectives

• Worksheets and handouts

• Lecture presentation outlines and enrichments

• Classroom activities

• Answers to study questions

• New Zealand instructor information

• Critical thinking questions with answers

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Understanding Nutrition

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PREFACE

Nutrition is a science. The details of a nutrient’s chemistry or a cell’s biology can be overwhelming and confusing to some, but it needn’t be. When the science is explained step by step and the facts are connected one by one, the details become clear and understandable. That has been the goal since this book was first developed and as it has continued to be updated in this fifth edition: to reveal the fascination of science and share the excitement of nutrition with readers. We have learned from the hundreds of university teachers and nutrition professionals and more than a million students who have used previous editions of this book through the years that readers want to understand nutrition so that they can make healthy choices in their daily lives. With its focus on Australia and New Zealand, the text incorporates current nutrition recommendations and public health issues, and food culture relevant to those studying and working in nutrition in this region of the world. Because nutrition is an active science, staying current is paramount. To that end, this edition incorporates the latest in nutrition research. The connections between diet and disease have become more apparent – and our interest in making smart health choices has followed. More people are living longer and healthier lives. The science of nutrition has grown rapidly, with new research emerging daily. In this edition, as with previous editions, every chapter has been substantially revised to reflect the many changes that have occurred in the field of nutrition and in our daily lives over the years. We hope that this book serves you well.

THE CHAPTERS

Understanding Nutrition presents the core information of an introductory nutrition course. The early chapters introduce the nutrients and their work in the body, and the later chapters apply that information to people’s lives – describing the role of foods and nutrients in energy balance and weight control, in physical activity, in the life cycle and in disease prevention, and food safety. At the beginning of each chapter are clearly stated learning objectives to outline the key concept areas to be covered. Each chapter also clearly flags for the reader practical applications of nutritional research and presents the most recent research in the topic area.

THE HIGHLIGHTS

Every chapter is followed by a highlight that provides readers with an in-depth look at a current, and often controversial, topic that relates to its companion chapter. Each highlight closes with critical thinking questions designed to encourage readers to develop clear, rational, open-minded and informed thoughts based on the evidence presented in the text.

THE APPENDICES

The appendices are valuable references for a number of purposes. Appendix A summarises background information on the hormonal and nervous systems, complementing Appendices B and C on basic chemistry, the chemical structures of nutrients and major metabolic pathways. Appendix D describes measures of protein quality. Appendix E provides detailed coverage of nutrition assessment with updated infant and child growth charts, and Appendix F presents estimated energy requirements for men and women at various levels of physical activity. Appendix G presents common calculation and conversion tips.

Chillis are part of the capsicum family and a rich source of vitamin C

xiv

THE COVERS

The book’s inside covers put commonly used information at your fingertips, including current nutrient recommendations and suggested weight ranges for various heights. We have taken great care to provide accurate information and have included many references at the end of each chapter. However, to keep the number of references manageable, many statements appear without references. All statements reflect current nutrition knowledge and the authors will supply references upon request. In addition to supporting text statements, the references provide readers with resources for finding a good overview or more details on a subject. In this new edition, the art and layout have been carefully designed to be inviting while enhancing student learning. For all chapters and highlights, content has been reviewed and updated. Several new figures and tables have been created and others revised to enhance learning. Each chapter also features a true–false ‘common sense’ test presented at the beginning to allow students to test their core knowledge on practical nutrition concepts related to the topic. Answers to these common-sense questions are revealed throughout the chapter and a brief explanation is given at the end. This new edition has also been revised throughout to include more content and related nutrition issues that are specific to New Zealand. For example, Chapter 2 features the recent updates to the Eating and Activity Guidelines for New Zealand Adults. And to acknowledge the growing interest in the gastrointestinal microbiome in health, an expanded section in Chapter 3 has been added with an additional focus on nutrition, the microbiome and mental health as well as a research focus in Chapter 4. Nutrition is a fascinating subject, and we hope our enthusiasm for it comes through on every page. Tim Crowe Adam Walsh Ellie Whitney Sharon Rady Rolfes

Dragon fruit seeds are an excellent source of Oleic and Linoleic acids which may lower risk of cardiovascular disease

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ABOUT THE AUTHORS

Eleanor Noss Whitney, PhD, received her BA in Biology from Radcliffe College in 1960 and her PhD in Biology from Washington University, St Louis, in 1970. Formerly on the faculties at Florida State University and Florida A&M University and a dietitian registered with the American Dietetic Association, Ellie now devotes full time to research, writing and consulting in nutrition, health and environmental issues. Her earlier publications include articles in science, genetics, and other journals. Her textbooks include Nutrition Concepts and Controversies 12th edn, Understanding Nutrition 12th edn, Understanding Normal and Clinical Nutrition 9th edn and Nutrition and Diet Therapy 7th edn, all with Cengage Wadsworth. She also recently co-authored Priceless Florida (Pineapple Press), a comprehensive text examining the ecosystems in her home state. Her additional interests include energy conservation, solar energy use, alternatively fuelled vehicles and ecosystem restoration. Sharon Rady Rolfes received her MS in nutrition and food science from Florida State University. She is a founding member of Nutrition and Health Associates, an information resource centre that maintains a research database on over 1000 nutrition-related topics. Sharon’s publications include the college textbooks Understanding Nutrition 12th edn and Nutrition for Health and Health Care 4th edn. In addition to writing and research, she occasionally teaches at Florida State University and serves as a consultant for various educational projects. Her volunteer work includes serving on the board of Working Well, a community initiative dedicated to creating a healthy workforce. Dr Tim Crowe is an Advanced Accredited Practising Dietitian who has spent most of his career in the world of university nutrition teaching and research. He now works chiefly as a health and medical writer and scientific consultant and speaks on many health topics to the public through both the media, social media and writing for consumer publications. Dr Adam Walsh is a Senior Lecturer in Nutrition and Dietetics in the School of Behavioural and Health Sciences at Australian Catholic University in Melbourne, and an Advanced Accredited Practising Dietitian. He teaches in the undergraduate and postgraduate nutrition and dietetics programs in the areas of clinical dietetics, nutritional physiology, and paediatric health. Adam’s area of research is the influence of fathers on young children’s nutrition and physical activity behaviours.

Compounds in garlic can help reduce blood pressure and improve cholesterol levels

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ACKNOWLEDGEMENTS

The adaptation and updating of this textbook has been a team effort with us all focused on improving a book that has been well-received throughout nutrition courses in Australia and New Zealand. Many thanks must go to the team of external reviewers who gave valuable feedback and advice on each of the chapters in order to improve the relevance of the text to the teaching of nutrition in Australia and New Zealand. The team at Cengage have been instrumental in guiding us through the entire process and have been a pleasure to work with through all stages of development. It is rewarding to see the text now in print after all our hard work. From Tim Crowe: Many thanks go to my nutrition and dietetic friends and colleagues who have been down the publication path before and assured me that the late nights and long weekends of writing and proofing would be time well spent in producing a piece of work to be proud of. They were right. From Adam Walsh: Thanks to my two wonderful boys for keeping me grounded and reminding me what life is all about. They have, on more than one occasion, reminded me that even though I’m the dietitian in the house, I’m still just Dad to them. The authors and Cengage Learning would like to thank our reviewers who provided incisive and helpful feedback: • Louise Brough – Massey University • Tamara Bucher – University of Newcastle, Central Coast Campus • Alison Coates – University of South Australia, City East • Cathryn Conlon – Massey University • Kirsten Fagan – Holmesglen Institute Waverley • Chris Irwin – Griffith University, Gold Coast • Peter Lerossignol – Australian Catholic University, Banyo • Isabelle Lys – Australian Catholic University, Banyo • Sophie Scott – Fitness Institute Australia.

Tumeric contains the potent anti-inflammatory curcumin

1

CHAPTER

1

AN OVERVIEW OF NUTRITION Nutrition in your life

Believe it or not, you have probably eaten at least 20 000 meals in your life. Without any conscious effort on your part, your body uses the nutrients from those meals to make all its components, fuel all its activities and defend itself against diseases. How successfully your body handles these tasks depends, in part, on your food choices. Nutritious food choices support healthy bodies. PUTTING COMMON SENSE TO THE TEST Circle your answer

T F For good health, it is best to avoid all processed foods. T F Fat has twice the number of kilojoules as carbohydrates or protein. T F All published research should be treated with some level of critical appraisal. T F A Recommended Dietary Intake for a nutrient is the amount that everyone needs to

consume each day.

T F Changing our diet will do little to reduce the risk of many chronic diseases.

LEARNING OBJECTIVES 1.1 Describe how various factors influence personal food choices. 1.2 Name six major classes of nutrients and identify which are organic and which yield energy. 1.3 Explain the scientific method and how scientists use various types of research studies and methods to acquire nutritional information.

1.4 Define the four categories of the Nutrient Reference Values (NRVs) and explain their purpose. 1.5 Explain how the four nutrition assessment methods for an individual are used to detect energy and nutrient deficiencies and excesses. 1.6 Identify several risk factors for chronic disease and explain their relationship. 1.7 Recognise misinformation and describe how to identify reliable nutrition information. Onions contain antioxidants and compounds that fight inflammation, decrease triglycerides and reduce cholesterol levels

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Understanding Nutrition

In general, a chronic disease progresses slowly or with little change and lasts a long time. By comparison, an acute disease develops quickly, produces sharp symptoms and runs a short course. • chronos = time • acute = sharp

Welcome to the world of nutrition. Although you may not always have been aware of it, nutrition has played a significant role in your life. And it will continue to affect you in major ways, depending on the foods you select. Every day, several times a day, you make food choices that influence your body’s health for better or worse. Each day’s choices may benefit or harm your health only a little, but when these choices are repeated over years and decades, the rewards or consequences become major. That being the case, paying close attention to good eating habits now can bring health benefits later. Conversely, carelessness about food choices can contribute to many chronic diseases prevalent in later life, including heart disease and cancer. Of course, some people will become ill or die young no matter what choices they make, and others will live long lives despite making poor choices. For most of us, however, the food choices we make each and every day will benefit or impair our health in proportion to the wisdom of those choices. Although most people realise that their food habits affect their health, they often choose foods for other reasons. After all, foods bring to the table a variety of pleasures, traditions and associations as well as nourishment. The challenge, then, is to combine favourite foods and fun times with a nutritionally balanced diet.

1.1  Food choices

People decide what to eat, when to eat and even whether to eat in highly personal ways, often based on behavioural or social motives rather than on an awareness of nutrition’s importance to health.

Personal preference As you might expect, the primary reason people choose foods is taste – they like certain flavours. Two widely shared preferences are for the sweetness of sugar and for the savouriness of salt. Liking high-fat foods also appears to be a universally common preference. Other preferences might be for the hot chilli common in Mexican cooking or the curry spices of Indian cuisine. Some research suggests that genetics may influence people’s food preferences.1

Hunger and satiety People eat for a variety of reasons, but clearly hunger is a key driver of seeking food. Hunger is a physiological response to a need for food triggered by chemical messengers originating and acting in the brain. After a meal, the feeling of satiety suppresses hunger and allows a person to not feel the need to eat for a while. The complex interplay between hunger, hormones and the feeling of fullness are covered in greater depth in Section 8.2 of Chapter 8 which explores energy balance and body composition.

Habit People sometimes select foods out of habit. They eat cereal every morning, for example, simply because they have always eaten cereal for breakfast. Eating a familiar food and not having to make any decisions can be comforting. Similarly, people may find certain foods and beverages most appropriate at certain times of day – orange juice in the morning, for example.

Ethnic heritage or tradition Among the strongest influences on food choices are ethnic heritage and tradition. People eat the foods they grew up eating. Every country – and, in fact, every region of a country – has its own typical foods and ways of combining them into meals. The ‘Australian diet’ includes many

Chapter 1: An overview of nutrition

3

ethnic foods from various countries, such as Greece, Italy, Thailand and China, all adding variety to the diet. The New Zealand diet has been influenced by British, Pacific and, more recently, Asian migrants. Recent trends in the New Zealand diet include a reduction in beef, lamb and potatoes and an increase in poultry, pasta and rice, which reflects international food trends, food prices and ease of preparation.2

Social interactions

Marketing

Getty Images/Fuse

Most people enjoy companionship while eating. It’s fun to go out with friends for pizza or Thai. Meals are social events, and sharing food is part of hospitality. Social customs invite people to accept food or drink offered by a host or shared by a group regardless of hunger signals. Such social interactions can be a challenge for people trying to limit their food intake; Chapter 9 describes how people tend to eat more food when socialising with others. People also tend to eat the kinds of foods eaten by those in their social circles, thus helping to explain why obesity seems to spread in social networks and weight loss is easier with a partner. An enjoyable way to learn about other cultures is to taste their ethnic foods.

The food industry competes for our food dollars, persuading consumers to eat more – more food, more often. These marketing efforts pay off well, generating billions of dollars in new sales each year. In addition to building brand loyalty, food companies attract busy consumers with their promises of convenience.

Availability, convenience and economy People eat foods that are accessible, quick and easy to prepare, and within their financial means. Today’s consumers value convenience and are willing to spend more than half of their food budget on meals that require little, if any, further preparation. Consumers’ food choices and behaviours shifted when the COVID-19 pandemic forced restaurants to close and trips to the supermarket were infrequent. But what was seen during this time was part of a longgrowing trend where people would frequently eat out, bring home ready-to-eat meals or have food delivered. Even when they venture into the kitchen, they want to prepare a meal in 15 to 20 minutes, using fewer than half a dozen ingredients – and those ‘ingredients’ are often semiprepared foods, such as canned soups. This emphasis on convenience limits food choices to the selections offered on menus and products designed for quick preparation. Whether decisions based on convenience meet a person’s nutrition needs depends on the choices made. Eating a banana or a chocolate bar may be equally convenient, but the fruit offers more vitamins and minerals and less sugar and fat. Given the abundance of convenient food options, fewer adults are learning the cooking skills needed to prepare meals at home, which has its downside. They are more likely to eat out where the choice is often low-cost fast-food outlets. People who are competent in their cooking skills eat more of their meals at home and tend to make healthier food choices.

Positive and negative associations People tend to like particular foods associated with happy occasions – such as meat pies at football games or cake at birthday parties. By the same token, people can develop aversions and dislike foods that they ate when they felt sick or that were forced on them.3 Similarly, children learn to like and dislike certain foods when their parents use foods as rewards or punishments. Negative experiences can have long-lasting influences on food preferences.

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Understanding Nutrition

Emotions

Alamy Stock Photo/Wave Royalty Free

Emotions are another factor that guide food choices and eating behaviours. Some people cannot eat when they are emotionally upset. Others may eat in response to a variety of emotional stimuli; such as, to relieve boredom or depression, or to calm anxiety. A lonely person may choose to eat rather than to call a friend. A person who has returned home from an exciting evening out may unwind with a late-night snack. These people may find emotional comfort, in part because foods can influence the brain’s chemistry and the mind’s response. Eating in response to emotions can easily lead to overeating and obesity, but it may be appropriate at times. For example, sharing food at times of grief serves both the giver’s need to provide comfort and the receiver’s need to be cared for and to interact with others, as well as to take nourishment. To enhance your health, keep nutrition in mind when selecting foods.

Values

Food choices may reflect people’s religious beliefs, political views or environmental concerns. For example, many Christians forgo meat during Lent (the period prior to Easter), Jewish law includes an extensive set of dietary rules that govern the use of foods derived from animals, and Muslims fast between sunrise and sunset during Ramadan (the ninth month of the Islamic calendar). A concerned consumer may boycott fruit picked by migrant workers who have been exploited. People may buy vegetables from local farmers to save the fuel and environmental costs of foods shipped in from far away. They may also select foods packaged in containers that can be reused or recycled. Some consumers accept or reject foods that have been irradiated or genetically modified, depending on their approval of these processes (see Chapter 19 and Highlight 19 for a complete discussion).

Body weight and health Sometimes people select certain foods and supplements that they believe will improve their body weight, health or allergies and avoid those they believe might be detrimental. Such decisions can be beneficial when based on nutrition science, but decisions based on fads or carried to extremes undermine good health, as pointed out in later discussions of eating disorders (Highlight 8) and dietary supplements commonly used by athletes (Highlight 14).

Nutrition and health benefits PUTTING COMMON SENSE TO THE TEST

For good health, it is best to avoid all processed foods. FALSE

Finally, of course, many consumers make food choices that will benefit their health. Making healthy food choices 100 years ago was rather easy; the list of options was relatively short, and markets sold mostly fresh, whole foods. Examples of whole foods include vegetables, legumes, fruits, seafood, meats, poultry, eggs, nuts, seeds, milk and whole grains. Today, tens of thousands of food items fill the shelves of super-grocery stores and most of those items are processed foods. Whether a processed food is a healthy choice depends, in part, on how extensively the food was processed. When changes are minimal, processing can provide an abundant, safe, convenient, affordable and nutritious product. Examples of minimally processed foods include frozen vegetables, fruit juices, smoked salmon, cheeses, and breads. The nutritional value diminishes, however, when changes are extensive, creating

Chapter 1: An overview of nutrition

ultra-processed foods. Ultra-processed foods no longer resemble whole foods. They are made from substances that are typically used in food preparation but not consumed as foods themselves (e.g. oils, fats, flours, refined starches and sugars). These substances undergo further processing by adding little, if any, processed foods, salt and other preservatives, and additives such as flavours and colours. Examples of ultra-processed foods include soft drinks, corn chips, confectionery, chicken nuggets and pastries. Notably, these foods cannot be made in a home kitchen using common grocery ingredients. Dominating the global foods market, ultra-processed foods tend to be attractive, tasty and cheap – as well as high in fat and sugar. Consumers who want to make healthy food choices will select fewer ultra-processed foods and more whole foods and minimally processed foods.4 CURRENT RESEARCH IN NUTRITION The perils of highly processed foods Do you believe the key to good health is to just cut out processed foods? The term ‘processed food’ may seem like a dietary demon that we need to avoid, but it is a concept that has little meaning and is unhelpful in informing food choices. Almost everything you eat is processed to an extent. Even cooking food is a form of food processing. A much more helpful concept is to divide food into categories based on their degree of processing. So, on the positive side think more of food that has been minimally processed and is still close to its natural state in appearance and nutritional quality. Here it is all about fruits vegetables, fruits, wholegrains, nuts, milk, fresh meats and legumes. And against that, we have the foods we should be most concerned about – ultra-processed foods. Ultra-processed foods are industrial formulations of food-derived substances that contain little if any whole food. Ultra-processed foods often include ingredients not commonly used in home cooking such as flavourings, colourings, emulsifiers and other additives. A key feature of ultra-processed foods is that they are usually appetising and pleasing to the taste buds, convenient, sold in large packages and highly marketed. Ultra-processed foods are the types of foods that are over-represented in the list of discretionary food choices. Such foods are not an essential part of a nutritious diet. Now nutritional researchers are linking these foods as a major driver of overweight and obesity, while also contributing to non-communicable diseases, such as heart disease, type 2 diabetes and certain cancers. A recent systematic review and meta-analysis looked at the links between ultra-processed foods and chronic disease.5 From 21 cross-sectional and 19 prospective studies, increasing consumption of ultra-processed foods was linked to a greater risk of overweight or obesity; metabolic syndrome; depression; cardiometabolic diseases, such as heart disease or diabetes; frailty; irritable bowel syndrome; cancer and all-cause mortality. Most of the food we eat is processed to some degree. But it is only the foods considered to be ultra-processed that we should aim to eat less of. Eating food as close to its natural state as possible, making food from original ingredients and choosing a wide variety of mostly plant-based foods are the keys to eating a healthy diet.

1.2 Nutrients

Biologically speaking, people eat to receive nourishment. Do you ever think of yourself as a biological being made of carefully arranged atoms, molecules, cells, tissues and organs? Are you aware of the activity going on within your body even as you sit still? The atoms, molecules and cells of your body continually move and change, even though the structures of your tissues

REVIEW IT

A person selects foods for a variety of reasons. Whatever those reasons may be, food choices influence health. Individual food selections neither make nor break a diet’s healthfulness, but the balance of foods selected over time can make an important difference to health. For this reason, people are wise to think ‘nutrition’ when making their food choices.

5

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Understanding Nutrition

and organs and your external appearance remain relatively constant. To maintain your ‘self’, you must continually replenish, from foods, the energy and the nutrients you deplete as your body maintains itself.

Nutrients in foods and in the body Shutterstock.com/Maridav

Amazingly, our bodies can derive all the energy, structural materials and regulating agents we need from the foods we eat. This section introduces the nutrients that foods deliver and shows how they participate in the dynamic processes that keep people alive and well.

Nutrient composition of foods Chemical analysis of a food such as a tomato shows that it is composed primarily of water (95%). Most As Chapter 5 of the solid materials are carbohydrates, lipids and proteins. If you could remove these explains, most lipids materials, you would find a tiny residue of vitamins, minerals and other compounds. Water, are fats. carbohydrates, lipids, proteins, vitamins and some of the minerals found in foods are nutrients – substances the body uses for the growth, maintenance and repair of its tissues. This book focuses mostly on nutrients; however, foods contain other compounds as well, such as fibre, FIGURE 1.1  Body composition of healthyphytochemicals, pigments, additives, alcohols and others. Some weight men and women The human body is made of compounds similar to those found in foods – mostly are beneficial, some are neutral and a few are harmful. Later water (60%) and some fat (13–21% for young men, sections of the book touch on these compounds and their 23–36% for young women who are of a healthy weight), significance. with carbohydrate, protein, vitamins, minerals and other minor constituents making up the remainder. (Chapter 8 describes the health hazards of too little or too much body fat.)

Nutrient composition of the body A complete chemical analysis of your body would show that it is made of materials similar to those found in foods (see Figure 1.1). A healthy 70 kilograms body contains about 41 kilograms of water and about 9 to 21 kilograms of fat. The remaining kilograms are mostly protein, carbohydrate and the major minerals of the bones. Vitamins, other minerals and incidental extras constitute a fraction of a kilogram.

Chemical composition of nutrients

Key: % Carbohydrates, proteins, vitamins, minerals in the body % Fat in the body % Water in the body

The simplest of the nutrients are the minerals. Each mineral is a chemical element; its atoms are all alike. As a result, its identity never changes; for example, iron may have different electrical charges, but individual iron atoms remain the same when they are in a food, when a person eats the food, when the iron becomes part of a red blood cell, when the cell is broken down and when the iron is lost from the body by excretion. The next simplest nutrient is water, a compound made of two elements – hydrogen and oxygen. Minerals and water are inorganic nutrients, which means they do not contain carbon. The other four classes of nutrients – carbohydrates, lipids, proteins and vitamins – are more complex. In addition to hydrogen and oxygen, they all contain carbon, an element

Chapter 1: An overview of nutrition

found in all living things. They are therefore called organic compounds (meaning, literally, alive). Protein and some vitamins also contain nitrogen and may contain other elements as well (see Table 1.1). The use of the term ‘organic’ when describing the chemistry of substances should not be confused with the use of this term in the farming and produce sense to describe how food is grown under a certification system, as Chapter 19 explains.

TABLE 1.1   Elements in the six classes of nutrients Notice that organic nutrients contain carbon. CARBON

HYDROGEN

OXYGEN

NITROGEN

MINERALS

Inorganic nutrients Minerals

✓

Water

✓

✓

Organic nutrients Carbohydrates

✓

✓

✓

Lipids (fats)

✓

✓

✓

Proteins

a

✓

✓

✓

Vitamins

✓

✓

✓

b

a

Some proteins also contain the mineral sulphur.

b

Some vitamins contain nitrogen; some contain minerals.

✓

Essential nutrients The body can make some nutrients, but it cannot make all of them. Also, it makes some in insufficient quantities to meet its needs and, therefore, must obtain these nutrients from foods. The nutrients that foods must supply are essential nutrients. When used to refer to nutrients, the word essential means more than just ‘necessary’; it means ‘needed from outside the body’ – normally from foods.

Energy-yielding nutrients: carbohydrate, fat and protein In the body, three organic nutrients can be used to provide energy: carbohydrate, fat and protein. In contrast to these energy-yielding nutrients, vitamins, minerals and water do not yield energy in the human body. Carbohydrate, fat, and protein are sometimes called macronutrients because the body requires them in relatively large amounts (many grams daily). In contrast, vitamins and minerals are micronutrients, required only in small amounts (milligrams or micrograms daily). Table 1.2 summarises some of the ways the six classes of nutrients can be described.

TABLE 1.2   The six classes of nutrients NUTRIENT

ORGANIC

INORGANIC

ENERGY-YIELDING

MACRONUTRIENT

Carbohydrates

✓

✓

✓

Lipids (fats)

✓

✓

✓

Proteins

✓

✓

✓

Vitamins

✓

MICRONUTRIENT

✓

Minerals

✓

Water

✓

✓

7

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Understanding Nutrition

Energy measured in kilojoules The international unit for measuring food energy is the joule, a measure of work energy. The energy in food is normally expressed in kilojoules. To convert kcalories to kilojoules, multiply by 4.2; to convert kilojoules to kcalories, multiply by 0.24.

PUTTING COMMON SENSE TO THE TEST

Fat has twice the number of kilojoules as carbohydrates or protein. TRUE

The energy released from carbohydrates, fats and proteins can be measured in joules. In some countries (particularly the US), ‘calorie’ is still the preferred measure of food energy, though in this context it is actually kilocalories (or kcalories) that is the implied unit of energy measure for food and the prefix of ‘kilo’ is normally dropped in everyday speaking. When you read in popular books or magazines that an apple provides ‘100 calories’, it actually means 100 kcalories, which is the same as 420 kilojoules. This book uses the term kilojoules and its abbreviation kJ throughout.

Energy from foods The amount of energy a food provides depends on how much carbohydrate, fat and protein it contains. When completely broken down in the body, a gram of carbohydrate yields about 17 kilojoules (4 kcals) of energy, a gram of protein also yields 17 kilojoules (4 kcals) and a gram of fat yields 37 kilojoules (9 kcals) (see Table 1.3). Fat, therefore, has a greater energy density than either carbohydrate or protein. The energy yield from carbohydrate of 17 kilojoules per gram (kJ/g) is considered an average figure as monosaccharides (e.g. glucose), disaccharides (e.g. sucrose) and starch all yield slightly different amounts of energy per gram. The upcoming ‘How to’ box explains how to calculate the energy available from foods.

TABLE 1.3   Kilojoule and kcalorie values of energy nutrients Notice that organic nutrients contain carbon. NUTRIENTS

ENERGY kJ/g

ENERGY kcal/g

Carbohydrate

17

4

Protein

17

4

Fat

37

9

Note: Alcohol contributes 29 kilojoules per gram that can be used for energy, but it is not considered a nutrient because it interferes with the body’s growth, maintenance and repair.

One other substance contributes energy – alcohol. Alcohol is not considered a nutrient because it interferes with the growth, maintenance and repair of the body, but it does yield energy (29 kJ or 7 kcal per gram) when metabolised in the body. (Highlight 7 and Chapter 18 present the potential harms and possible benefits of alcohol consumption.) Most foods contain all three energy-yielding nutrients as well as water, vitamins, minerals and other substances. For example, meat contains water, fat, vitamins and minerals as well as protein. Bread contains water, a trace of fat, a little protein and some vitamins and minerals in addition to its carbohydrate. Only a few foods are exceptions to this rule, the common ones being sugar (pure carbohydrate) and oil (essentially pure fat).

Energy in the body The processes by which nutrients are broken down to yield energy or used to make body structures are known as metabolism, which is defined and described further in Chapter 7.

The body uses the energy-yielding nutrients to fuel all its activities. When the body uses carbohydrate, fat or protein for energy, the bonds between the nutrient’s atoms break. As the bonds break, they release energy. Some of this energy is released as heat, but some is used to send electrical impulses through the brain and nerves, to synthesise body compounds and to move muscles. Thus the energy from food supports every activity, from quiet thought to vigorous sports. If the body does not use these nutrients to fuel its current activities, it rearranges them into storage compounds (e.g. body fat), to be used between meals and overnight when fresh energy supplies run low. If more energy is consumed than expended, the result is an increase in energy stores and weight gain. Similarly, if less energy is consumed than expended, the result is a decrease in energy stores and weight loss. When consumed in excess of energy needs, alcohol, too, can be converted to body fat and stored. When alcohol contributes a substantial portion of the energy in a person’s diet, the

Chapter 1: An overview of nutrition

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harm it does far exceeds the problems of excess body fat. (Highlight 7 describes the effects of alcohol on health and nutrition.)

Other roles of energy-yielding nutrients In addition to providing energy, carbohydrates, fats and proteins provide the raw materials for building the body’s tissues and regulating its many activities. In fact, protein’s role as a fuel source is relatively minor compared with the other two nutrients and its other roles. Proteins are found in structures such as the muscles and skin and help to regulate activities such as digestion and energy metabolism.

HOW TO:

CALCULATE THE ENERGY AVAILABLE FROM FOODS

Practise calculating the energy available from foods. To calculate the energy available from 1.  a food, multiply the number of grams of carbohydrate, protein and fat by 17, 17 and 37, respectively. Then add the results together – e.g. 1 slice of bread with 1 tablespoon of peanut butter on it contains 16 grams carbohydrate, 7 grams protein and 9 grams fat.

16 g carbohydrate × 17 kJ/g = 272 kJ 7 g protein × 17 kJ/g = 119 kJ 9 g fat × 37 kJ/g = 333 kJ Total = 724 kJ

From the information you calculated in step 1, you can determine the percentage of kilojoules each of the energy nutrients contributes to the total. 2. To determine the percentage of kilojoules from fat, for example, divide the 333 fat kilojoules by the total 724 kilojoules. 3.  Then multiply by 100 to get the percentage.

333 fat kJ ÷ 724 total kJ = 0.46 0.46 × 100 = 46%

Dietary recommendations that urge people to limit fat intake to 20 to 35 per cent of kilojoules refer to the day’s total energy intake, not to individual foods. Still, if the proportion of fat in each food choice throughout a day exceeds 35 per cent of kilojoules, then the day’s total surely will, too. Knowing that this snack provides 46 per cent of its kilojoules from fat alerts a person to the need to make lower-fat selections at other times that day.

Vitamins Vitamins are organic but they do not provide energy. Instead, they facilitate the release of energy from carbohydrate, fat and protein and participate in numerous other activities throughout the body. Each of the 13 different vitamins has its own special role to play. One vitamin enables the eyes to see in dim light, another helps produce functional red blood cells, and still another helps make the sex hormones – among other things. When you cut yourself, one vitamin helps stop the bleeding and another helps repair the skin. Vitamins busily help replace old red blood cells and the lining of the digestive tract. Almost every action in the body requires the assistance of vitamins. Vitamins can function only if they are intact, but because they are complex organic molecules, they are vulnerable to destruction by heat, light and chemical agents. This is why the body handles them carefully, and why nutrition-wise cooks do, too. The strategies of cooking vegetables at moderate temperatures for short times and using small amounts of water help to preserve the vitamins.

The water-soluble vitamins are vitamin C and the eight B vitamins: thiamin, riboflavin, niacin, vitamins B6 and B12, folate, biotin and pantothenic acid. The fat-soluble vitamins are vitamins A, D, E and K. The water-soluble vitamins are the subject of Chapter 10, and the fat-soluble vitamins are discussed in Chapter 11.

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Understanding Nutrition

Minerals

Shutterstock.com/marcstock

In the body, some minerals are put together in orderly arrays in such structures as bones and teeth. Minerals are also found in the fluids of the body, which influences fluid properties. Whatever their roles, minerals do not yield energy. Only 16 minerals are known to be essential in human nutrition. The major minerals are calcium, phosphorus, potassium, sodium, chloride, magnesium and sulphate. The trace minerals are iron, iodine, zinc, chromium, selenium, fluoride, molybdenum, copper and manganese. (Chapters 12 and 13 are devoted to the major and trace minerals, respectively.) Others are being studied to determine whether they play significant roles in the human body. Still other minerals are environmental contaminants that displace the nutrient minerals from their workplaces in the body, disrupting body functions. The problems caused by contaminant minerals are described in Chapter 13. Because minerals are inorganic, they are indestructible and do not require the special care that vitamins do. Minerals can, however, be bound by substances that interfere with the body’s ability to absorb them. They can also be lost during food-refining processes or during cooking when they leach into water that is discarded. Water itself is an essential nutrient and carries many minerals naturally.

Water

Water, indispensable and abundant, provides the environment in which nearly all the body’s activities are conducted. It participates in many metabolic reactions and supplies the medium for transporting vital materials to cells and carrying waste products away from them. Water is discussed fully in Chapter 12 but is mentioned in every chapter. REVIEW IT

Foods provide nutrients – substances that support the growth, maintenance and repair of the body’s tissues. The six classes of nutrients are: • carbohydrates • vitamins •  lipids (fats) • minerals • proteins • water. Foods rich in the energy-yielding nutrients (carbohydrates, fats and proteins) provide the major materials for building the body’s tissues and yield energy for the body’s use or storage. Energy is measured in kilojoules. Vitamins, minerals and water facilitate a variety of activities in the body.

1.3  The science of nutrition

The science of nutrition is the study of the nutrients and other substances in foods and the body’s handling of them. It has its foundation in several other sciences, including biology, biochemistry, and physiology. Nutrition is a relatively young science, but much has happened in its short life. And it is currently experiencing a tremendous growth spurt as scientists apply knowledge gained from sequencing the human genome. The integration of nutrition, genomics and molecular biology has opened a new world of study called nutritional genomics – the science of how nutrients affect the activities of genes and how genes affect the interactions between diet and disease. Highlight 6 describes how nutritional genomics is shaping the science of nutrition, and examples of nutrient–gene interactions appear throughout later sections of the book.

Chapter 1: An overview of nutrition

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What has the field of nutritional research achieved in the way of significant discoveries over the last 30 years? And what are the greatest challenges for the coming 30 years? These questions were debated by an eminent panel of nutrition experts at a symposium in Wageningen, the Netherlands, and their viewpoints (see Table 1.4) make for an interesting summary of the milestone discoveries in nutrition.6 The research area of the gut microbiome and its implications for our health has exploded since the list was compiled in 2009 and this would now be a worthy addition. The gut microbiome is discussed in greater depth in Chapter 3. As for future challenges, controlling obesity and insulin resistance, delaying cognitive decline by diet, and restoring the balance between private and public control of nutritional research are all considered top priorities.

TABLE 1.4   Greatest discoveries in nutritional research in the past 30 years RANK

DISCOVERY

1

Folic acid supplements reduce the risk of birth defects

2

Health effects of trans fatty acids

3

Nutritional regulation of gene transcription

4

Progress in measuring energy intake – from questionnaires to doubly labelled water

5

Fat tissue as an endocrine organ

6

The LDL-cholesterol receptor and its regulation by diet

7

Obesity is a normal response to an abnormal environment

8

Alcohol causes breast cancer

9

Body fatness is the second most avoidable cause of cancer

10

Plant stanols and sterols and their effects on lipid metabolism

11

Diabetes can be prevented by diet and lifestyle

12

Interaction of carbohydrate/glycaemic load with insulin resistance

13

Vitamin E supplements do not reduce the risk of cardiovascular disease

14

Long-chain polyunsaturated fatty acids reduce mortality in coronary heart disease patients

15

The multisystemic role of vitamin D

Adapted from M. B. Katan and co-authors, ‘Which are the Greatest Recent Discoveries and the Greatest Future Challenges in Nutrition?’, European Journal of Clinical Nutrition, 63 (2009): 2−10.

Conducting research Consumers sometimes depend on personal experience or social media to gather information on nutrition. Known as anecdotes, such personal accounts of an experience are not accepted as reliable scientific information. In contrast, researchers use the scientific method to guide their work (see Figure 1.2 and the glossary for definitions of research terms). As the figure shows, research always begins with a problem or a question. For example, ‘What foods or nutrients might protect against the common cold?’ In search of an answer, scientists make an educated guess (hypothesis), such as ‘foods rich in vitamin C reduce the number of common colds’. Then they systematically conduct research studies to collect data that will test the hypothesis. Some examples of various types of research designs are presented in Figure 1.3. Each type of study has strengths and weaknesses (see Table 1.5), and, consequently, some provide stronger evidence than others.

A personal account of an experience or event is an anecdote and is not accepted as reliable scientific information.

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FIGURE 1.2   The scientific method Research scientists follow the scientific method. Note that most research generates new questions, not final answers. Thus the sequence begins anew, and research continues in a somewhat cyclical way. OBSERVATION AND QUESTION Identify a problem to be solved or ask a specific question to be answered.

HYPOTHESIS AND PREDICTION Formulate a hypothesis – a tentative solution to the problem or answer to the question – and make a prediction that can be tested.

EXPERIMENT Design a study and conduct the research to collect relevant data.

RESULTS AND INTERPRETATIONS Summarise, analyse, and interpret the data; draw conclusions.

HYPOTHESIS SUPPORTED

THEORY Develop a theory that integrates conclusions with those from numerous other studies.

HYPOTHESIS NOT SUPPORTED

NEW OBSERVATIONS AND QUESTIONS

Controls In studies examining the effectiveness of vitamin C in treating the common cold, for example, researchers typically divide the subjects into two groups. One group (the experimental group) receives a vitamin C supplement, and the other (the control group) does not. Researchers observe both groups to determine whether one group has fewer or shorter colds than the other. The following discussion describes some of the pitfalls inherent in an experiment of this kind and ways to avoid them. In sorting subjects into two groups, researchers must ensure that each person has an equal chance of being assigned to either the experimental group or the control group. This is accomplished by randomisation; that is, the subjects are chosen randomly from the same population by flipping a coin or some other method involving chance. Randomisation helps to ensure that results reflect the treatment and not factors that might influence the grouping of subjects.

Chapter 1: An overview of nutrition

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FIGURE 1.3   Examples of research designs North Atlantic Ocean

EPIDEMIOLOGICAL STUDIES France

Slovenia

Croatia

Black Sea

Bosnia Italy

Montenegro Albania

Spain

Greece

Morocco

Algeria

Mediterranean Sea Tunisia

Heart attacks

Science Photo Library/Dr M. A. Ansary

Libya

Turkey

Lebanon Israel Jordan

Cross-sectional Researchers observe how much and what kinds of foods a group of people eat and how healthy those people Syria are. Their findings identify factors that might influence the incidence of a disease in various populations.

Example: The people of the Mediterranean region drink lots of wine, eat plenty of fat from olive oil and have a lower incidence of heart disease than northern Europeans and Australians.

Egypt

Case-control Researchers compare people who do and do not have a given condition such as a disease, closely matching them in age, gender and other key variables so that differences in other factors will stand out. These differences may account for the condition in the group that has it.

Example: People with goitre lack iodine in their diets.

Cohort Researchers analyse data collected from a selected group of people (a cohort) at intervals over a certain period of time.

Example: Data collected periodically over the past several decades from over 5000 people randomly selected from the town of Framingham, Massachusetts, in 1948 have revealed that the risk of heart attack increases as blood cholesterol increases.

EXPERIMENTAL STUDIES

laboratory where all conditions can be controlled.

Shutterstock.com/wavebreakmedia

iStock.com/Mediaphotos

Getty Images/Remi Benali

Blood cholesterol

Laboratory-based animal studies Researchers feed animals special diets that provide or omit specific nutrients and then observe any changes in health. Such studies test possible disease causes and treatments in a

Example: Mice fed a high-fat diet eat less food than mice given a lower-fat diet, so they receive the same number of kilojoules – but the mice eating the fat-rich diet become severely obese.

Laboratory-based in-vitro studies Researchers examine the effects of a specific variable on a tissue, cell or molecule isolated from a living organism.

Example: Laboratory studies find that fish oils inhibit the growth and activity of the bacteria implicated in ulcer formation.

Human intervention (or clinical) trials Researchers ask people to adopt a new behaviour (for example, eat a citrus fruit, take a vitamin C supplement or exercise daily). These trials help determine the effectiveness of such interventions on the development or prevention of disease.

Example: Heart disease risk factors improve when men receive fresh squeezed orange juice daily for two months compared with those on a diet low in vitamin C – even when both groups follow a diet high in saturated fat.

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Understanding Nutrition

TABLE 1.5   Strengths and weaknesses of research designs TYPE OF RESEARCH

STRENGTHS

WEAKNESSES

Epidemiological studies determine the incidence and distribution of diseases in a population. Epidemiological studies include cross-sectional, case-control and cohort (see Figure 1.3)

• Can narrow down the list of possible causes • Can raise questions to pursue through other types of studies

• Cannot control variables that may influence the development or the prevention of a disease • Cannot prove cause and effect

Laboratory-based studies explore the effects of a specific variable on a tissue, cell or molecule. Laboratory-based studies are often conducted in test tubes (in vitro) or on animals

• Can control conditions • Can determine effects of a variable

• Cannot apply results from test tubes or animals to human beings

Human intervention or clinical trials involve human beings who follow a specified regimen

• Can control conditions (for the most part) • Can apply findings to some groups of human beings

• Cannot generalise findings to all human beings • Cannot use certain treatments for clinical or ethical reasons

Importantly, the two groups of people must be similar and must have the same track record with respect to colds to rule out the possibility that observed differences in the rate, severity or duration of colds might have occurred anyway. If, for example, the control group would normally catch twice as many colds as the experimental group, then the findings prove nothing. In experiments involving a nutrient, the diets of both groups must also be similar, especially with respect to the nutrient being studied. If those in the experimental group were receiving less vitamin C from their usual diet, then any effects of the supplement may not be apparent.

Sample size To ensure that chance variation between the two groups does not influence the results, the groups must be large. For example, if one member of a group of five people catches a bad cold by chance, they will pull the whole group’s average towards bad colds; but if one member of a group of 500 catches a bad cold, they will not unduly affect the group average. Statistical methods are used to determine whether differences between groups of various sizes support a hypothesis.

Placebos

If people who take vitamin C for colds believe it will cure them, their chances of recovery may improve. Taking anything believed to be beneficial may hasten recovery. This phenomenon, the result of expectations, is known as the placebo effect. In experiments designed to determine vitamin C’s effect on colds, this mind–body effect must be rigorously controlled. One way researchers control for the placebo effect is to give pills to all participants. Those in the experimental group, for example, receive pills containing vitamin C, and those in the control group receive a placebo – pills of similar appearance and taste containing an inactive ingredient. This way, the expectations of both groups will be equal. It is not necessary to convince all subjects that they are receiving vitamin C, but the extent of belief or unbelief must be the same in both groups. A study conducted under these conditions is called a blind experiment – that is, the subjects do not know (are blind to) whether they are members of the experimental group (receiving treatment) or the control group (receiving the placebo).

Double blind When neither the subjects nor the researchers know which subjects are in which group, the study is called a double-blind experiment. Being fallible human beings and having an emotional and sometimes a financial investment in a successful outcome, researchers might

Chapter 1: An overview of nutrition

record and interpret results with a bias in the expected direction. To prevent such bias, the pills would be coded by a third party, who does not reveal to the researchers which subjects were in which group until all results have been recorded.

Analysing research findings Research findings must be analysed and interpreted with an awareness of each study’s limitations. Scientists must be cautious about drawing any conclusions until they have accumulated a body of evidence from multiple studies that have used various types of research designs. As evidence accumulates, scientists begin to develop a theory that integrates the various findings and explains the complex relationships.

PUTTING COMMON SENSE TO THE TEST

All published research should be treated with some level of critical appraisal. TRUE

Correlations and causes Researchers often examine the relationships between two or more variables – for example, daily vitamin C intake and the number of colds or the duration and severity of cold symptoms. Importantly, researchers must be able to observe, measure or verify the variables selected. Findings sometimes suggest no correlation between variables (regardless of the amount of vitamin C consumed, the number of colds remains the same). Other times, studies find either a positive correlation (the more vitamin C, the more colds) or a negative correlation (the more vitamin C, the fewer colds). Correlational evidence proves only that the variables are associated, not that one is the cause of the other. People often jump to conclusions when they notice correlations, but their conclusions are often wrong. To prove that A causes B, scientists have to find evidence of the mechanism – that is, an explanation of how A might cause B.

Knowledge about the nutrients and their effects on health comes from scientific study.

Cautious conclusions When researchers record and analyse the results of their experiments, they must exercise caution in their interpretation of the findings. For example, in an epidemiological study, scientists may use a specific segment of the population (e.g. men aged 18–30 years). When the scientists draw conclusions, they are careful not to generalise the findings to older men or women of any age or to imply a cause-and-effect relationship.7 Similarly, scientists performing research studies using animals are cautious in applying their findings to humans. Conclusions from any one research study are always tentative and take into account findings from studies conducted by other scientists. As evidence accumulates, scientists gain confidence about making recommendations that affect people’s health and lives. Still, their statements are worded cautiously, such as ‘A diet high in fruits and vegetables may protect against some cancers’.

Evaluating the reliability of research Wherever or however nutrition information is presented, it pays to retain a healthy scepticism. However, there are some ways in which the question of evaluating reliability can be approached more systematically. For research published in a journal, the findings are evaluated by a board of reviewers composed of other scientists who rigorously evaluate the study to assure that the scientific method was followed – a process known as peer review. The reviewers critique the study’s hypothesis, methodology, statistical significance and conclusions. They also note the funding source, recognising that financial support and other conflicts of interest may bias scientific conclusions.8 If the reviewers consider the conclusions to be well supported by the evidence – that is, if the research has validity – they endorse the work for publication in a scientific journal where others can read it. This raises an important point regarding

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information found on the internet: much gets published without the rigorous scrutiny of peer review. Consequently, readers must assume greater responsibility for examining the data and conclusions presented – often without the benefit of journal citations. Highlight 1, found later in this chapter, gives guidance in determining whether website information is reliable. Table 1.6 describes the parts of a typical research article.

TABLE 1.6   Parts of a typical research article Abstract

• Provides a brief overview of the article

Introduction

• Clearly states the purpose of the current study and provides a comprehensive review of the relevant literature

Methodology

• Defines key terms and describes the study design, subjects, and procedures used in conducting the study

Results

• Report the findings and may include tables and figures that summarise the information

Discussion

• Draws tentative conclusions that are supported by the data and reflect the original purpose as stated in the introduction. Usually, it answers a few questions and raises several more

References

• Reflect the investigator’s knowledge of the subject and should include an extensive list of relevant studies

Even when a new finding is published or released to the media, it is still only preliminary and not very meaningful by itself. Other scientists will need to confirm or disprove the findings through replication. To be accepted into the body of nutrition knowledge, a finding must stand up to rigorous, repeated testing in experiments performed by several different researchers. What we ‘know’ in nutrition results from years of replicating study findings. Communicating the latest finding in its proper context without distorting or oversimplifying the message is a challenge for scientists and journalists alike. For a helpful scientific overview of topics in nutrition, look for review articles in scholarly journals, such as Nutrition Reviews. A review may be either a systematic review, which provides a qualitative summary of the evidence and attempts to minimise bias in its interpretation or a meta-analysis, which provides a quantitative summary. With each report from scientists, the field of nutrition changes a little – each finding contributes another piece to the whole body of knowledge. People who know how science works understand that single findings, like single frames in a movie, are just small parts of a larger story. Over time, nutrition knowledge gradually changes, and dietary recommendations change to reflect the current understanding of scientific research. Highlight 5 provides a detailed look at how dietary fat recommendations have evolved over the past several decades as researchers have uncovered the relationships between the various kinds of fat and their roles in supporting or harming health. REVIEW IT

Scientists learn about nutrition by conducting experiments that follow the protocol of scientific research. Researchers take care to establish similar control and experimental groups, large sample sizes, placebos and blind treatments. Their findings must be reviewed and replicated by other scientists before being accepted as valid.

1.4  Nutrient Reference Values

Using the results of thousands of research studies, nutrition experts have produced a set of standards that define the amounts of energy, nutrients, other dietary components and physical activity that best support health. These recommendations are called Nutrient Reference Values (NRVs) and they reflect the collaborative efforts of researchers in both Australia and

Chapter 1: An overview of nutrition

New Zealand.9 The inside-cover pages of this book provide a handy reference for the NRVs. There is also a handy online calculator at https://www.nrv.gov.au/nutrients-energy-calc to determine your own individual nutrient and energy needs.

Establishing nutrient recommendations The NRV Working Party consisted of highly qualified scientists who based their estimates of nutrient needs on careful examination and interpretation of scientific evidence. These recommendations apply to healthy people and may not be appropriate for people with diseases that increase or decrease nutrient needs. The next few paragraphs discuss specific aspects of how the committee went about establishing the values that make up the NRV: • Estimated Average Requirement (EAR) • Recommended Dietary Intake (RDI) • Adequate Intake (AI) • Upper Level of Intake (UL). A further set of values, termed Suggested Dietary Targets (SDTs), was also established. These relate to nutrients for which there was a reasonable body of evidence indicating a potential chronic disease preventive effect at levels substantially higher than the EAR, RDI or AI.

Estimated Average Requirement (EAR)

The NRV Working Party reviewed hundreds of research studies to determine the requirement for each nutrient – how much is needed in the diet. The working party selected a different criterion for each nutrient based on its various roles in performing activities in the body and in reducing disease risks. An examination of all the available data reveals that each person’s body is unique and has its own set of requirements. Men differ from women, and needs change as people grow from infancy to old age. For this reason, recommendations for people are clustered into groups based on age and sex. Even so, the exact requirements for people of the same age and sex are likely to be different. For example, person A might need 40 units of a particular nutrient each day, person B might need 35 and person C might need 57. Looking at enough people might reveal that their individual requirements fall into a symmetrical distribution, with most near the midpoint and only a few at the extremes (see the left-hand side of Figure 1.4). Using this information, the working party determined an Estimated Average Requirement (EAR) for each nutrient – the average amount that appears sufficient for half of the population. In Figure 1.4, the EAR is shown as 45 units.

FIGURE 1.4   Estimated Average Requirement (EAR) and Recommended Dietary Intake (RDI) compared

B

20

30

EAR Number of people

Number of people

EAR

A

B

C 40

50

60

70

20

30

RDI

A C 40

50

60

70

Daily requirement for nutrient X (units/day)

Daily requirement for nutrient X (units/day)

The EAR for a nutrient is the amount that meets the needs of about half of the population (shown here by the red line).

The RDI for a nutrient (shown here in green) is set well above the EAR, meeting the needs of about 98 per cent of the population.

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PUTTING COMMON SENSE TO THE TEST

A Recommended Dietary Intake for a nutrient is the amount that everyone needs to consume each day. FALSE

Recommended Dietary Intake (RDI)

Once a nutrient requirement is established, the working party had to decide what intake to recommend for everybody – the Recommended Dietary Intake (RDI). As you can see by the distribution in Figure 1.4, the EAR (shown in the figure as 45 units) is probably closest to everyone’s need. However, if people consumed exactly the average requirement of a given nutrient each day, half of the population would develop deficiencies of that nutrient – in Figure 1.4, for example, person C would be among them. Recommendations are therefore set high enough above the EAR to meet the needs of most healthy people. Small amounts above the daily requirement do no harm, whereas amounts below the requirement may lead to health problems. When people’s nutrient intakes are consistently deficient (less than the requirement), their nutrient stores decline, and over time this decline leads to poor health and deficiency symptoms. Therefore, to ensure that the nutrient RDI meet the needs of as many people as possible, the RDI are set near the top end of the range of the population’s estimated requirements. In this example, a reasonable RDI might be 63 units a day (see the right side of Figure 1.4). Such a point can be calculated mathematically so that it covers about 98 per cent of a population. Almost everybody – including person C, whose needs were higher than the average – would be covered if they met this dietary goal. Relatively few people’s requirements would exceed this recommendation, and even then, they wouldn’t exceed it by much.

Adequate Intake (AI) For some nutrients, there is insufficient scientific evidence to determine an EAR (which is needed to set an RDI). In these cases, the working party established an Adequate Intake (AI) instead of an RDI. An AI reflects the average amount of a nutrient that a group of healthy people consumes. Like the RDI, the AI may be used as nutrient goals for individuals. Although both the RDI and the AI serve as nutrient intake goals for individuals, their differences are noteworthy. An RDI for a given nutrient is based on enough scientific evidence to expect that the needs of almost all healthy people will be met. An AI, on the other hand, must rely more heavily on scientific judgements because sufficient evidence is lacking. The percentage of people covered by an AI is unknown; an AI is expected to exceed average requirements, but it may cover more or fewer people than an RDI would cover (if an RDI could be determined). For these reasons, AI values are more tentative than RDI. The table on the inside back cover identifies which nutrients have an RDI and which have an AI. Later chapters present the RDI and AI values for the vitamins and minerals.

Upper Level of Intake (UL) Individual tolerances for high doses of nutrients vary and somewhere above the recommended intake is a point beyond which a nutrient is likely to become toxic. This point is known as the Upper Level of Intake (UL). It is naive – and inaccurate – to think of recommendations as minimum amounts. A more accurate view is to see a person’s nutrient needs as falling within a range, with marginal and danger zones both below and above it (see Figure 1.5). Paying attention to upper levels is particularly useful in guarding against the overconsumption of nutrients, which may occur when people use large-dose supplements and fortified foods regularly. Later chapters discuss the dangers associated with excessively high intakes of vitamins and minerals, and the inside cover presents tables that include the upperlevel values for selected nutrients.

Establishing energy recommendations In contrast to the RDI and AI values for nutrients, the recommendation for energy is not generous. Excess energy cannot be readily excreted and is eventually stored as body fat. These reserves may be beneficial when food is scarce, but they can also lead to obesity and its associated health consequences.

Chapter 1: An overview of nutrition

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FIGURE 1.5   Inaccurate versus accurate view for nutrient intakes The RDI or AI for a given nutrient represents a point that lies within a range of appropriate and reasonable intakes between toxicity and deficiency. Both of these recommendations are high enough to provide reserves in times of short-term dietary inadequacies, but not so high as to approach toxicity. Nutrient intakes above or below this range may be equally harmful. Danger of toxicity

Marginal

Tolerable Upper Intake Level

Safety Intake

Safety RDI or AI RDI

Estimated Average Requirement

Marginal Danger

Inaccurate view

Danger of deficiency Accurate view

Estimated Energy Requirement (EER)

The energy recommendation – called the Estimated Energy Requirement (EER) – represents the average dietary energy intake (kJ per day) that will maintain energy balance in a person who has a healthy body weight and FIGURE 1.6   Energy nutrient contributions level of physical activity. Appendix F lists EER values for children and to the total adults engaging in different levels of physical activity. Balance is the The three energy nutrients – carbohydrate, fat, and protein – all contribute to the total energy key to the energy recommendation. Enough energy is needed to sustain intake. Each of these three bars illustrates a healthy and active life, but too much energy can lead to weight gain percentages that fall within the AMDR. Notice and obesity. Because any amount in excess of energy needs will result in that whenever the percentage of any one of them weight gain, no upper level for energy has been determined.

Acceptable Macronutrient Distribution Range (AMDR) People do not eat energy directly; they derive energy from foods containing carbohydrate, fat and protein. Each of these three energyyielding nutrients contributes to the total energy intake, and those contributions vary in relation to each other. The NRV Working Party determined that the composition of a diet that provides adequate energy and nutrients, maintains current body weight and reduces the risk of chronic diseases is: • 45–65 per cent kilojoules from carbohydrate • 20–35 per cent kilojoules from fat • 15–25 per cent kilojoules from protein. These values are known as Acceptable Macronutrient Distribution Range (AMDR). Figure 1.6 illustrates that diets with varying amounts of carbohydrate, fat, and protein can all fall within the AMDR and when the contribution of any of the energy nutrients increases or decreases, the contribution of the others shifts as well. The following ‘How to’ box explains how to convert AMDR percentages into kilojoules and grams.

increases or decreases, the contribution of the others shifts as well. 100 80

10%

15% 35%

25%

35% 60 40

20% 65% 45%

20 0

Key: Protein Fat Carbohydrate

50%

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Understanding Nutrition

HOW TO: CALCULATE THE AMDR IN GRAMS AND KILOJOULES The Acceptable Macronutrient Distribution Range (AMDR) present the amounts of carbohydrate, fat, and protein for a healthy diet as a percentage of the total energy intake. The previous ‘How To’ shows how to calculate the percentage each of the energy nutrients contributes to the total. Those percentages can then be used to determine whether intakes fall within the AMDR. Alternatively, you can calculate the amounts of carbohydrate, fat, and protein in kilojoules or grams based on AMDR goals. Consider a daily energy intake of 8000 kilojoules, for 1  example. Multiply total energy intake by 45 per cent to find the lower end of the carbohydrate AMDR, and then divide by 17 to convert kilojoules to grams. 2 Now multiply total energy intake by 65 per cent to find the upper end of the carbohydrate AMDR, and then divide by 17 to convert kilojoules to grams. 3 For carbohydrate, the AMDR of 45–65 per cent for an 8000-kilojoule diet is 3600–5200 kilojoules, or 212– 306 grams. Similar calculations can be done for fat and protein AMDR. Multiply total energy intake by 20 per cent to find the lower end of the fat AMDR (and by 35 per cent to find the upper end), and then divide by 37 to convert kilojoules to grams. Multiply total energy intake by 10 per cent to find the lower end of the protein AMDR (and by 35 per cent to find the upper end), and then divide by 17 to convert kilojoules to grams.

8000 kJ x 0.45 = 3600 kJ 3600 kJ ÷ 17 g/kJ = 212 g

8000 kJ x 0.65 = 5200 kJ 5200 kJ ÷ 17 g/kJ = 306 g

TRY IT Calculate the kilojoules and grams of carbohydrate, fat, and protein of a meal plan that provides 9200 kilojoules, with 50 per cent carbohydrate, 30 per cent fat, and 20 per cent protein.

Using nutrient recommendations Although the intent of nutrient recommendations seems simple, they are the subject of much misunderstanding and controversy. Perhaps the following facts will help put them in perspective: 1 Estimates of adequate energy and nutrient intakes apply to healthy people. They need to be adjusted for malnourished people or those with medical problems who may require supplemented or restricted intakes. 2 Recommendations are not minimum requirements, nor are they necessarily optimal intakes for all individuals. They can only target ‘most’ of the people and cannot account for individual variations in nutrient needs. 3 Most nutrient goals are intended to be met through diets composed of a variety of foods whenever possible. Because foods contain mixtures of nutrients and non-nutrients, they deliver more than just those nutrients covered by the recommendations. Excess intakes of vitamins and minerals are unlikely when they come from foods rather than supplements. 4 Recommendations apply to average daily intakes. Trying to meet the recommendations for every nutrient every day is difficult and unnecessary. The length of time over which a person’s intake can deviate from the average without risk of deficiency or overdose varies for each nutrient, depending on how the body uses and stores the nutrient. For most nutrients (e.g. thiamin and vitamin C), deprivation would lead to rapid development of deficiency symptoms (within days or weeks); for others (e.g. vitamin A and vitamin B12), deficiencies would develop more slowly (over months or years).

Chapter 1: An overview of nutrition

5 Each of the NRV categories serves a unique purpose. For example, the EARs are most appropriately used to develop and evaluate nutrition programs for groups such as schoolchildren or military personnel. The RDI (or AI if an RDI is not available) can be used to set goals for individuals. The UL serves as a reminder to keep nutrient intakes below amounts that increase the risk of toxicity – not a common problem when nutrients derive from foods, but a real possibility for some nutrients if supplements are used regularly. With these understandings, professionals can use the NRV for a variety of purposes. Using the online NRV calculator at http://www.nrv.gov.au you can gain a practical understanding of your own requirements.

Comparing nutrient recommendations At least 80 different nations and international organisations have published nutrient standards similar to those used in Australia and New Zealand. Slight differences may be apparent, reflecting differences both in the interpretation of the data from which the standards were derived and in the food habits and physical activities of the populations they serve. Terminologies may also vary between countries. For example, North America uses the term Dietary Reference Intakes (DRI) in place of NRV and adopts the term Recommended Dietary Allowance (RDA) instead of RDI. In the United Kingdom, Dietary Reference Values (DRV) are used, with Reference Nutrient Intake (RNI) used in place of RDI. Recommendations have also been developed by two international groups – the FAO (Food and Agriculture Organization) and WHO (World Health Organization). The FAO/WHO recommendations are considered sufficient to maintain health in nearly all healthy people worldwide.

1.5  Nutrition assessment

What happens when a person does not get enough or gets too much of a nutrient or energy? If the deficiency or excess is significant over time, the person will exhibit signs of malnutrition. With a deficiency of energy, the person may display the symptoms of undernutrition by becoming extremely thin, losing muscle tissue and becoming prone to infection and disease. With a deficiency of a nutrient, the person may experience skin rashes, depression, hair loss, bleeding gums, muscle spasms, night blindness or other symptoms. With an excess of energy, the person may become obese and vulnerable to diseases associated with overnutrition, such as heart disease and diabetes. With a sudden nutrient overdose, the person may experience hot flushes, yellowing skin, a rapid heart rate, low blood pressure or other symptoms. Similarly, over time, regular intakes in excess of needs may also have adverse effects. This discussion presents the basics of nutrition assessment; many more details are offered in later chapters and in Appendix E.

REVIEW IT

The Nutrient Reference Values (NRV) are a set of nutrient intake values that can be used to plan and evaluate diets for healthy people. The Estimated Average Requirement (EAR) defines the amount of a nutrient that supports a specific function in the body for half of the population. The Recommended Dietary Intake (RDI) is based on the EAR and establishes a goal for dietary intake that will meet the needs of almost all healthy people. An Adequate Intake (AI) serves a similar purpose when an RDI cannot be determined. The Suggested Dietary Target (SDT) is a daily average intake from food and beverages for certain nutrients that may help in prevention of chronic disease. The Estimated Energy Requirement (EER) defines the average amount of energy intake needed to maintain energy balance, and the Acceptable Macronutrient Distribution Range (AMDR) defines the proportions contributed by carbohydrate, fat and protein to a healthy diet. The Upper Level of Intake (UL) establishes the highest amount that appears safe for regular consumption.

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Understanding Nutrition

Nutrition assessment of individuals To prepare a nutrition assessment, a dietitian or other trained healthcare professional uses: • historical information • anthropometric data • physical examinations • laboratory tests. Each of these methods involves collecting data in various ways and interpreting each finding in relation to the others to create a total picture. Nutrition screening is often the first part of the process to help identify people who are already malnourished or at risk of becoming so. After nutritional screening, nutrition assessment can then be undertaken. Nutrition assessment differs from nutrition screening by its use of a comprehensive assessment of a person’s nutrition status through such measures as health, medication use, diet histories, anthropometric and laboratory tests.

Historical information One step in evaluating nutrition status is to obtain information about a person’s history with respect to health status, socioeconomic status, medication use and diet. The health history reflects a person’s medical record and may reveal a disease that interferes with the person’s ability to eat or the body’s use of nutrients. The person’s family history of major diseases is also noteworthy, especially for conditions such as heart disease that have a genetic tendency to run in families. Economic circumstances may show a financial inability to buy foods or inadequate kitchen facilities in which to prepare them. Social factors, such as marital status, ethnic background and educational level, also influence food choices and nutrition status. A drug history, including all prescribed and over-the-counter medications as well as narcotics, may highlight possible interactions that lead to nutrient deficiencies (as described in Highlight 17). A diet history that examines a person’s intake of foods, beverages and supplements may reveal either a surplus or inadequacy of nutrients or energy. To take a diet history, the assessor collects data about the foods a person eats. The data may be collected by recording the foods the person has eaten over a period of 24 hours, three days, or a week or more, or by asking what foods the person typically eats and how much of each. The days in the record must be fairly typical of the person’s diet, and portion sizes must be recorded accurately. To determine the amounts of nutrients consumed, the assessor usually enters the foods and their portion sizes into a computer using a diet analysis program. The assessor then compares the calculated nutrient intakes with the NRV to determine the probability of adequacy (see Figure 1.7). Alternatively, the diet history might be compared

FIGURE 1.7   Using the NRV to assess the dietary intake of a healthy individual High Usual intake of nutrient X (units/day)

22

Low

Intake probably adequate

If a person’s usual intake falls above the RDI, the intake is probably adequate because the RDI covers the needs of almost all people.

RDI Intake possibly inadequate

A dual intake that falls between the RDI and the EAR is more difficult to assess; the intake may be adequate, but the chances are greater or equal that it is inadequate.

EAR Intake probably inadequate

If the usual intake falls below the EAR, it is probably inadequate.

Chapter 1: An overview of nutrition

23

against standards such as the Australian Guide to Healthy Eating, the Australian Dietary Guidelines or the Eating and Activity Guidelines for New Zealand Adults (described in Chapter 2). An estimate of energy and nutrient intakes from a diet history, when combined with other sources of information, can help confirm or rule out the possibility of suspected nutrition problems. A sufficient intake of a nutrient does not guarantee adequacy, and an insufficient intake does not always indicate a deficiency. Such findings, however, warn of possible problems.

Anthropometric data

A second technique that may help to reveal nutrition problems is taking anthropometric measures, such as height and weight. The assessor compares a person’s measurements with standards specific for gender and age or with previous measures on the same individual. (Chapter 8 presents information on body weight and its standards.) Measurements taken periodically and compared with previous measurements reveal patterns and indicate trends in a person’s overall nutrition status, but they provide little information about specific nutrients. Instead, measurements out of line with expectations may reveal such problems as children’s failure to thrive, the wasting or swelling of body tissues in adults, and obesity – conditions that may reflect energy or nutrient deficiencies or excesses.

Physical examinations A third nutrition assessment technique is a physical examination looking for clues to poor nutrition status. Every part of the body that can be inspected may offer such clues: hair, eyes, skin, posture, tongue, fingernails and others. The examination requires skill because many physical signs reflect more than one nutrient deficiency or toxicity – or even non-nutrition conditions. Like the other assessment techniques, a physical examination alone does not yield firm conclusions. Instead, physical examinations reveal possible imbalances that must be confirmed by other assessment techniques, or they confirm results from other assessment measures.

Laboratory tests A fourth way to detect a developing deficiency, imbalance or toxicity is to take samples of blood or urine, analyse them in the laboratory and compare the results with normal values for a similar population. A goal of nutrition assessment is to uncover early signs of malnutrition before symptoms appear, and laboratory tests are most useful for this purpose. In addition, they can confirm suspicions raised by other assessment methods.

Iron, for example The mineral iron can be used to illustrate the stages in the development of a nutrient deficiency and the assessment techniques useful in detecting them. The overt, or outward, signs of an iron deficiency appear at the end of a long sequence of events. Figure 1.8 describes what happens in the body as a nutrient deficiency progresses, and shows which assessment methods can reveal those changes. First, the body has too little iron – either because iron is lacking in the person’s diet (a primary deficiency) or because the person’s body doesn’t absorb enough, excretes too much or uses iron inefficiently (a secondary deficiency). A diet history provides clues to primary deficiencies; a health history provides clues to secondary deficiencies. Next, the body begins to use up its stores of iron. At this stage, the deficiency might be described as subclinical. It exists as a covert condition, and although it might be detected by laboratory tests, no outward signs are apparent. Finally, the body’s iron stores are exhausted. Now it cannot make enough iron-containing red blood cells to replace those that are ageing and dying. Iron is needed in red blood cells to carry oxygen to all the body’s tissues. When iron is lacking, fewer red blood cells are made, the

Assessment may one day depend on measures of how a nutrient influences genetic activity within the cells, instead of quantities in the blood or other tissues.

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Understanding Nutrition

FIGURE 1.8   Stages in the development of a nutrient deficiency Internal changes precede outward signs of deficiencies. However, outward signs of sickness need not appear before a person takes corrective measures. Laboratory tests can help determine nutrient status in the early stages. WHAT HAPPENS IN THE BODY

WHICH ASSESSMENT METHODS REVEAL CHANGES

Primary deficiency caused by inadequate diet or Secondary deficiency caused by problem inside the body

Diet history

Declining nutrient stores (subclinical) and Abnormal functions inside the body (covert)

Physical signs and symptoms (overt)

Health history

Laboratory tests

Physical examination and anthropometric measures

new ones are pale and small, and every part of the body feels the effects of oxygen shortage. Now the overt symptoms of deficiency appear – weakness, fatigue, pallor and headaches – reflecting the iron-deficient state of the blood. A physical examination will reveal these symptoms.

Nutrition assessment of populations To assess a population’s nutrition status, researchers conduct surveys using techniques similar to those used on individuals. The data collected are then used by various agencies for numerous purposes, including the development of national health goals.

National nutrition surveys National nutrition surveys gather information about the population’s dietary, nutritional, and related health status. The US, the UK and many continental European nations have had ongoing, systematic programs for monitoring the diet and nutritional status of their populations for many years. Australia has conducted only four national surveys of diet in the past 40 years: a national dietary survey of adults in 1983, one of children in 1985, the National Nutrition Survey in 1995 and the most recent National Health Survey in 2017–18.10 In the absence of a regular, comprehensive and coordinated national nutrition monitoring survey in Australia, several state and territory governments have established monitoring systems that survey health behaviours, including food habits. In New Zealand, Adult Nutrition Surveys were carried out by the Ministry of Health in 1997 and 2008–09 and the National Children’s Nutrition Survey was carried out in 2002.11 The Ministry of Health also collects information as part of its ongoing Health Survey, which includes some dietary habits questions and self-reported weight and height.12 The information gained from national nutrition surveys is used for a variety of purposes. For example, the government uses this information to establish public policy on nutrition education, public health nutrition programs and the regulation of the food supply. Scientists

Chapter 1: An overview of nutrition

use the information to establish research priorities. The food industry uses these data to guide decisions in public relations and product development. The NRV and other major reports that examine the relationships between diet and health depend on the information collected from these nutrition surveys. These data also provide the basis for developing and monitoring national health goals.

National trends What do we eat and how has it changed over the past 60 years? The short answer to both questions is ‘a lot’. We eat more meals away from home, particularly at fast-food restaurants. We eat larger portions. We drink more sweetened beverages and eat more energy-dense, nutrient-poor foods, such as lollies and chips. We snack frequently. As a result of these dietary habits, our energy intake has risen and, consequently, so has the incidence of overweight and obesity. Overweight and obesity, in turn, profoundly influence our health – as the next section explains. REVIEW IT

People become malnourished when they get too little or too much energy or nutrients. Deficiencies, excesses and imbalances of nutrients lead to malnutrition diseases. To detect malnutrition in individuals, healthcare professionals use four nutrition assessment methods. Reviewing dietary data and health information may suggest a nutrition problem in its earliest stages. Laboratory tests may detect it before it becomes overt, whereas anthropometrics and physical examinations pick up on the problem only after it causes symptoms. National surveys use similar assessment methods to measure people’s food consumption and to evaluate the nutrition status of populations.

1.6  Diet and health

Diet has always played a vital role in supporting health. Early nutritional research focused on identifying the nutrients in foods that would prevent such common diseases as rickets and scurvy, the vitamin D- and vitamin C-deficiency diseases. With this knowledge, industrialised countries have successfully defended against nutrient deficiency diseases. More recently, nutritional research has focused on chronic diseases associated with energy and nutrient excesses. Once thought to be ‘rich countries’ problems’, overconsumption of unhealthy foods and chronic diseases have escalated worldwide in recent decades.

Chronic diseases Table 1.7 lists the 10 leading causes of death in Australia. These ‘causes’ are stated as if a single condition, such as heart disease, caused death, but most chronic diseases arise from multiple factors over many years. A person who dies of heart disease may have been overweight, had high blood pressure, been a cigarette smoker, and spent years eating a diet high in saturated fat and getting too little exercise. In New Zealand, the leading causes of death in 2018 were cancer, ischaemic heart diseases and cerebrovascular diseases (with 114, 48 and 23.1 deaths per 100 000 population, respectively).13 Of course, not all people who die of heart disease fit this description, and nor do all people with these characteristics die of heart disease. People who are overweight might die from the complications of diabetes instead, or those who smoke might die of lung cancer. They might even die from something totally unrelated to any of these factors, such as a car accident. Still, statistical studies have shown that certain conditions and behaviours are linked to certain diseases. Notice that Table 1.7 highlights five of the top 10 causes of death as having a link with diet. Coronary heart disease, colorectal cancer, stroke and diabetes account for a quarter of all deaths each year. Sometimes the problem is a matter of ‘too much’, as is true for sodium, processed meats, red meats, and sugar-sweetened beverages. Other times, the problem is a matter of ‘too little’, as is true for nuts and seeds, seafood omega-3 fats, vegetables, fruits, whole grains, and polyunsaturated fats.

PUTTING COMMON SENSE TO THE TEST

Changing our diet will do little to reduce the risk of many chronic diseases. FALSE

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Understanding Nutrition

TABLE 1.7   Leading causes of death in Australia (2019) PERCENTAGE OF TOTAL DEATHS 1

Ischaemic heart disease

10.8

2

Dementia including Alzheimer’s disease

8.9

3

Cerebrovascular disease (stroke)

5.9

4

Lung cancer

5.2

5

Chronic lower respiratory diseases

5.0

6

Colorectal cancer

3.2

7 Diabetes

2.9

8

Lymph and blood cancer

2.8

9

Influenza and pneumonia

2.4

10 Diseases of the urinary system

2.3

Note: The diseases highlighted in blue have relationships with diet. Australian Bureau of Statistics, Causes of Death, Australia, ABS Catalogue Number 3303.0, (Canberra: ABS, 2020). CC BY 2.5 Australia.

Risk factors for chronic diseases

iStock.com/Sportstock

Factors that increase or reduce the risk of developing chronic diseases can be identified by analysing statistical data. A strong association between a risk factor and a disease means that when the factor is present, the likelihood of developing the disease increases. It does not mean that all people with the risk factor will develop the disease. Similarly, a lack of risk factors does not guarantee freedom from a given disease. On the average, though, the more risk factors in a person’s life, the greater that person’s chances of developing the disease. Conversely, the fewer risk factors in a person’s life, the better the chances for good health.

Risk factors persist Physical activity can be both fun and beneficial.

Risk factors tend to persist over time. Without intervention, a young adult with high blood pressure will most likely continue to have high blood pressure as an older adult, for example. Thus, to minimise the damage, early intervention is most effective.

Risk factors cluster Risk factors tend to cluster. For example, a person who is obese may be physically inactive, have high blood pressure and have high blood cholesterol – all risk factors associated with heart disease. Interventions that focus on one risk factor often benefit the others as well; for example, physical activity can help reduce weight. The physical activity and weight loss will, in turn, help to lower blood pressure and blood cholesterol.

Risk factors in perspective

Cigarette smoking is responsible for over one in every 10 deaths each year.

The most prominent factors contributing to death in Australia (see Table 1.8)14 and New Zealand all have dietary and lifestyle causes. Risk factors, such as smoking, poor dietary habits, physical inactivity and alcohol consumption are personal behaviours that can be changed. Decisions to not smoke, to eat a well-balanced diet, to engage in regular physical activity and to drink alcohol in moderation (if at all) improve the likelihood that a person will enjoy good health. For this reason, guidelines, such as the Australian Guide to Healthy Eating and Australian Dietary Guidelines (both described in Chapter 2), have been developed to help individuals and health authorities determine what constitutes a healthy diet that will help lower disease risk.

Chapter 1: An overview of nutrition

TABLE 1.8   Factors contributing to deaths and disease burden in Australia RISK FACTOR

PERCENTAGE OF TOTAL DALYa

Tobacco

9.0

Alcohol

5.1

Physical inactivity

5.0

High body mass

5.5

High blood pressure

4.9

High plasma glucose

2.7

High cholesterol

2.4

Diet low in fruit

2.0

Diet low in vegetables

1.1

Diet low in whole grains

1.1

DALY: Disability-Adjusted Life Year. The DALY is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. a

Australian Institute of Health and Welfare, Australian Burden of Disease Study: impact and causes of illness and death in Australia 2011, (2016). CC-BY 3.0 Licence. (https://www.aihw.gov.au/copyright). https://www.aihw.gov.au/reports/burden-ofdisease/abds-impact-and-causes-of-illness-death-2011/contents/highlights

APPLICATIONS OF NUTRITIONAL RESEARCH The key dietary patterns of long-term health Diet plays a big part in health. As the typical Western diet moved to more overly refined and energy dense foods, rates of obesity and type 2 diabetes mirrored this change. A major scientific review has taken things back to basics to reinforce where the best health gains are to be found with diet.15 The review looked at the diet and chronic disease links from 304 meta-analyses and systematic reviews published in the last 63 years. Type 2 diabetes, overweight and obesity, cancer and cardiovascular disease together accounted for most of the chronic disease links found. As for dietary patterns, the findings showed that plant-based foods were more protective against the risk of developing chronic disease compared with animal-based foods. Among plant foods, grain-based foods seemed to have a small edge over fruits and vegetables. So much for the anti-grain sentiment that is popular at the moment! For animal-based foods, dairy products overall were considered neutral on health, and fish was considered protective. Red and processed meats were linked to a higher disease risk. For tea-lovers, the research confirmed this popular drink as being the most protective against disease risk. On the other end of the spectrum, to no-one’s surprise, soft drinks had few redeeming health benefits. The findings from this major review are close to a carbon copy of existing dietary guidelines that have changed little over decades. Eat more plant-based foods than animal foods, choose whole grains over refined grains, limit red and processed meat and choose other beverages in preference to soft drink. Such recommendations may not get media attention or help sell books in numbers like the latest fad diet, but they are the cornerstone of long-term health. Other risk factors, such as genetics, sex and age, also play important roles in the development of chronic diseases, but they cannot be changed. Health recommendations acknowledge the influence of such factors on the development of disease, but they must focus on the factors that are changeable. For the two out of three Australians who do not smoke or drink alcohol excessively, the one choice that can influence long-term health prospects more than any other is diet.

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Understanding Nutrition

The next several chapters provide many more details about nutrients and how they support health. Whenever appropriate, the discussion shows how diet influences each of today’s major diseases. Dietary recommendations appear again and again, as each nutrient’s relationships with health are explored. Most people who follow the recommendations will benefit and can enjoy good health into their later years. REVIEW IT

Within the range set by genetics, a person’s choice of diet influences long-term health. Diet has no influence on some diseases but is linked closely to others. Personal life choices, such as engaging in physical activity and using tobacco or alcohol, also affect health, for better or worse.

Chapter 1: An overview of nutrition

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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 For good health, it is best to avoid all processed foods. FALSE

Most foods are processed to a degree and many of these foods are healthy for us. It is more the ‘ultra-processed’ foods that we should limit in our diet.

2 Fat has twice the number of kilojoules as carbohydrates or protein. TRUE

Fat has 37 kJ/g compared with 17 kJ/g for carbohydrate and protein.

3 All published research should be treated with some level of critical appraisal. TRUE

4 A Recommended Dietary Intake for a nutrient is the

amount that everyone needs to consume each day. FALSE



An RDI is set at the level of meeting the needs of 98 per cent of the population it is targeting. Most people require less than this, but a small number require more.

5 Changing our diet will do little to reduce the risk of many chronic diseases. FALSE

Diet plays a large role in causing many of the chronic diseases we are faced with today, such as cancer, heart disease, stroke and diabetes.

No one research study is perfect, so any interpretation of a study should be done within the context of the study design limitations.

NUTRITION PORTFOLIO Each chapter in this book ends with simple ‘Nutrition portfolio’ activities that invite you to review key messages and consider whether your personal choices are meeting the dietary goals introduced in the text. By keeping a journal of these ‘Nutrition portfolio’ assignments, you can examine how your knowledge and behaviours change as you progress in your study of nutrition. Your food choices play a key role in keeping you healthy and reducing your risk of chronic diseases.

• •

•

For the foods and snacks you eat over a typical day, identify the factors that most influence your choices. List the chronic disease risk factors and conditions (see Table 1.8) that you or members of your family have. Describe lifestyle changes you can make to improve your chances of enjoying good health.

STUDY QUESTIONS Multiple choice questions

4

Answers can be found at the back of the book. 1

2

habit ethnic heritage or tradition personal preference social interactions.

5

essential nutrients conditionally essential nutrients non-essential nutrients organic nutrients.

The inorganic nutrients are: a b c d

carbohydrates, proteins and fats vitamins and minerals minerals and water water and proteins.

6

fats, minerals and water minerals, proteins and vitamins carbohydrates, fats and vitamins carbohydrates, fats and proteins.

Studies of populations that reveal correlations between dietary habits and disease incidence are termed: a b c d

Nutrients the human body must obtain from the diet because they cannot be made internally are called: a b c d

3

a b c d

When people eat the foods that are influenced by the companionship of friends and family in a group, their choices are influenced by: a b c d

The energy-yielding nutrients are:

clinical trials laboratory studies randomised trials epidemiological studies.

An experiment in which the researchers know who is receiving the treatment but the subjects do not is known as: a b c d

single blind double control double blind placebo control.

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Understanding Nutrition

7

An EAR for a nutrient represents: a b c d

8

the average amount of a nutrient that a group of healthy people consume the lowest amount of a nutrient that will maintain a specified criterion of adequacy the highest amount of a nutrient that appears safe for most healthy people the daily nutrient intake level estimated to meet the requirements of half the healthy individuals in a particular life stage and gender group.

9

a b c d

overt deficiency covert deficiency primary deficiency secondary deficiency.

10 Behaviours such as smoking, dietary habits, physical activity and alcohol consumption that influence the development of disease are known as: a b c d

Historical information, physical examinations, laboratory tests and anthropometric measures are: a b c d

A deficiency caused by an inadequate dietary intake is a(n):

techniques used in diet planning steps used in the scientific method approaches used in disease prevention methods used in a nutrition assessment.

risk factors chronic causes preventive agents disease descriptors.

REVIEW QUESTIONS 1

Give several reasons (and examples) why people make the food choices that they do. (Section 1.1)

2

What is a nutrient? Name the six classes of nutrients found in foods. What is an essential nutrient? (Section 1.2)

3

Which nutrients are inorganic and which are organic? Discuss the significance of that distinction. (Section 1.2)

4

Which nutrients yield energy and how much energy do they yield per gram? How is energy measured? (Section 1.2)

5

Describe the process for calculating the energy available from foods. (Section 1.2)

6

What is the science of nutrition? Describe the types of research studies and methods used in acquiring nutrition information. (Section 1.3)

7

What are the strengths and weaknesses of the different types of research designs? (Section 1.3)

8

What are the NRV? To whom do they apply? How are they used? In your description, identify the categories of NRV and indicate how they are related. (Section 1.4)

9

What judgement factors are involved in setting the energy and nutrient recommendations? (Section 1.4)

10 What happens when people get either too little or too much energy or nutrients? Define malnutrition, undernutrition and overnutrition. Describe the four methods used to detect energy and nutrient deficiencies and excesses. (Section 1.5) 11 What methods are used in nutrition surveys? What kinds of information can these surveys provide? (Section 1.6) 12 Describe risk factors and their relations to disease (Section 1.6) 13 Describe the leading causes of death and their relationships to diet and lifestyle factors. (Section 1.6)

NUTRITION CALCULATIONS Many chapters end with problems to give you practice in doing simple nutrition-related calculations. Although the situations are hypothetical, the numbers are real, and calculating the answers (see the answers section at the back of this book) provides a valuable nutrition lesson. Once you have mastered these examples, you will be prepared to examine your own food choices. Be sure to show your calculations for each problem. 1

Calculate the energy provided by a food’s energynutrient contents. A cup of fried rice contains 5 grams protein, 30 grams carbohydrate and 11 grams fat.

a





b

How many kilojoules does the rice provide from these energy nutrients? ______________ = ____ kJ protein ______________ = ____ kJ carbohydrate ______________ = ____ kJ fat Total = ____ kJ What percentage of the energy in the fried rice comes from each of the energy-yielding nutrients? ______________ = ____ % kJ from protein ______________ = ____ % kJ from carbohydrate ______________ = ____ % kJ from fat Total = ____ %

Chapter 1: An overview of nutrition

Note: The total should add up to 100%, but 99% or 101% due to rounding is also acceptable. c Calculate how many of the 460 kilojoules provided by a 150-millilitre glass of white wine come from alcohol, if the wine contains 0.4 grams of protein and 0.4 grams of carbohydrate. (NOTE: The remaining kilojoules derive from alcohol.) 0.4 g protein = ____ kJ protein 0.4 g carbohydrate = ____ kJ carbohydrate = ____ kJ alcohol Total = ____ %

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How many grams of alcohol does this represent? ____ g alcohol 2

To apply your nutrition knowledge to identify bogus claims, consider an advertisement for a new ‘superfood protein supplement’ that claims to contain 20 grams of protein and 50 kilojoules per dose. Is this possible? ____ Why or why not? ____ = ____ kJ

•

Read about the Selected Highlights from the 2017–18 National Health Survey https://www.abs.gov.au/ statistics/health/health-conditions-and-risks/ national-health-survey-first-results/2017-18 Read about food and nutrition monitoring in New Zealand by searching ‘nutrition survey’ at http://www. health.govt.nz Visit the food and nutrition centre at the Mayo Clinic: http://www.mayohealth.org

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search for ‘nutrition’ at the National Health and Medical Research Council site: http://www.nhmrc. gov.au • Review the Nutrient Reference Values: http://www. nrv.gov.au • Review nutrition recommendations from the Food and Agriculture Organization of the United Nations and the World Health Organization: http://www.fao.org and http://www.who.org

•

•

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Understanding Nutrition

HIGHLIGHT

1

1.7 NUTRITION INFORMATION AND MISINFORMATION: ON THE NET AND IN THE NEWS

Do keto diets really help with weight loss, or is it better to practise intermittent fasting? What is plant-based eating all about? Will nutrigenomics have the answers to all our health questions? Is the microbiome helpful or harmful? Food and nutrition trends such as these have always swirled around the world of nutrition. Some arise out of the latest research and have the backing of scientific evidence. They have staying power, whereas those based on nonsense fade away as soon as the next fanciful trend catches our attention. Upcoming chapters present the scientific findings of these and other trending topics, but it is most important that readers be able to spot a trend and determine its validity. How can people distinguish valid nutrition information from misinformation? One excellent approach is to notice who is providing the information. The ‘who’ behind the information is not always evident, though, especially in the world of electronic media. Keep in mind that people create apps, blogs, and websites on the internet, just as people write books and report the news. In all cases, consumers need to determine whether the person is qualified to provide nutrition information. This highlight begins by examining the unique potential as well as the problems of relying on the internet and the media for nutrition information. It continues with a discussion of how to identify reliable nutrition information that applies to all resources, including the internet and the news. (The Glossary defines related terms.) This discussion recognises that identifying nutrition misinformation requires more than simply gathering accurate information, although that is a good start; it requires critical thinking. Critical thinking allows a person who has gathered information to: • understand the connections between concepts • identify and evaluate the pros and cons of an argument • detect inconsistencies and errors • solve problems • identify the relevance of information. To that end, the questions at the end of the highlights that follow all chapters are intended to help develop critical thinking skills.

Nutrition on the net Got a question? The internet has an answer. The internet offers endless opportunities to obtain highquality information, but it also delivers an abundance of incomplete, misleading or inaccurate information. Simply put, anyone can publish anything. Determining whether information is balanced, accurate, and credible has become increasing challenging in recent years.1 With hundreds of millions of websites, a person searching for valid nutrition information can be overwhelmed with uncertainty. When using the internet, keep in mind that the quality of health-related information available covers a broad range. You must evaluate websites for their accuracy, just like every other source. The ‘How to’ box that follows provides tips for determining whether a website is reliable. One of the most trustworthy sites used by scientists and others is the US National Library of Medicine’s PubMed, which provides free access to over 30 million research papers published in scientific journals around the world. Many abstracts provide links to websites where full articles are available. Figure H1.1 introduces this valuable resource. If you have received an email warning of the health dangers associated with reusing or freezing plastic water bottles, you have been a victim of urban scarelore. When nutrition information arrives in unsolicited emails, be suspicious if: • the person sending it to you did not write it and you cannot determine who did or if that person is a nutrition expert • the phrase ‘Forward this to everyone you know’ appears • the phrase ‘This is not a hoax’ appears; chances are that it is • the news is sensational and you have never heard about it from legitimate sources • the language is emphatic and the text is sprinkled with capitalised words and exclamation marks • no references are given or, if present, are of questionable validity when examined.

Chapter 1: An overview of nutrition

33

FIGURE H1.1 PubMed: Internet resource for scientific nutrition references

Source: National Library of Medicine, US, https://pubmed.ncbi.nlm.nih.gov

The US National Library of Medicine’s PubMed website offers tutorials to help teach beginners to use the search system effectively. Often, simply visiting the site, typing a query in the ‘Search for’ box and clicking ‘Search’ will yield satisfactory results. For example, to find research concerning calcium and bone health, typing ‘calcium bone’ nets over 10 000 results. Try setting limits on dates, types of articles, languages and other criteria to obtain a more manageable number of abstracts to peruse.

Nutrition in the news Consumers get much of their nutrition information from television news, ‘current affairs’ programs and magazine reports, which have heightened awareness of how diet influences the development of diseases. Sometimes, however, when magazine articles or television programs report nutrition trends, they can mislead consumers and create confusion. They often tell a lopsided story based on a few testimonials instead of presenting the results of research studies or a balance of expert opinions. Tight deadlines and limited understanding sometimes make it difficult to provide a thorough report. Hungry for

the latest news, the media often report scientific findings prematurely – without the benefit of careful interpretation, replication and peer review. As a result, ‘surprising new findings’ seem to contradict one another, and consumers feel frustrated and betrayed. Occasionally the reports are downright false, but more often the apparent contradictions are simply the normal result of science at work. A single study contributes to the big picture, but when viewed alone, it can easily distort the image. To be meaningful, the conclusions of any study must be presented cautiously within the context of other research findings.

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Understanding Nutrition

HOW TO: DETERMINE WHETHER A WEBSITE IS RELIABLE To determine whether a website offers reliable nutrition information, ask the following questions: › Who is responsible for the site? Is it staffed by qualified professionals? Look for the authors’ names and credentials. Have experts reviewed the content for accuracy? › When? When was the site last updated? Because nutrition is an ever-changing science, sites need to be dated, and updated frequently. › Where? Where is the information coming from? The three letters following the dot in a Web address identify the site’s affiliation. Addresses ending in ‘gov’ (government), ‘edu’ (educational institute) and ‘org’ (organisation) generally provide reliable information; ‘com’ (commercial) sites represent businesses and, depending on their qualifications and integrity, may or may not offer dependable information. › Why? Why is the site giving you this information? Is the site providing a public service or selling a product? Many commercial sites provide accurate information, but some do not. When money is the prime motivation, be aware that the information may be biased. If you are satisfied with the answers to all the questions above, then ask this final question: › What? What is the message and is it in line with other reliable sources? Information that contradicts common knowledge should be questioned. Many reliable sites provide links to other sites to facilitate your quest for knowledge, but this provision alone does not guarantee a reputable intention. Be aware that any site can link to any other site without permission.

Televised talk shows frequently offer health advice – most commonly, dietary advice. Such advice may sound valid, especially when delivered by a doctor, but viewers need to remember that the primary purpose of these programs is entertainment and selling products. One study examining 160 episodes of two popular medical talk shows found that fewer than half of the recommendations were based on evidence.2

Identifying nutrition experts Regardless of whether the medium is electronic, print or video, consumers need to ask whether the person behind the information is qualified to speak on nutrition. If the creator of a website recommends eating three pineapples a day to lose weight, a trainer at the gym praises a highprotein diet or a health-store sales assistant suggests a herbal supplement, should you believe these people? Can you distinguish between accurate news reports and infomercials on television? Have you noticed that many televised nutrition messages are presented by celebrities, fitness experts, psychologists, food editors and chefs – that is, almost anyone except a qualified dietitian or nutritionist? When you are confused or need sound dietary advice, whom should you ask?

Doctors and other healthcare professionals Many people turn to doctors or other healthcare professionals for dietary advice, expecting them to know

about all health-related matters. But are they the best sources of accurate and current information on nutrition? Doctors acknowledge that nutrition plays a crucial role in health and agree that providing nutrition advice is part of their role, but barriers such as lack of nutrition education training and time constraints during appointments can reduce their role.3 By comparison, most students reading this text are taking a dedicated nutrition subject that may also form part of a nutrition degree or nutrition major. Most healthcare professionals appreciate the connections between health and nutrition. Those who have specialised in clinical nutrition are especially well qualified to speak on the subject. Few, however, have the time or experience to develop a nutrition care plan or provide detailed dietary advice for clients. Often, they wisely refer clients to a qualified nutritionist or dietitian. An accredited practising dietitian (APD) in Australia is credentialled by Dietitians Australia (DA), and a New Zealand Registered Dietitian (NZRD) would be registered by the New Zealand Dietitians Board (NZDB) Te Mana - Kai with many registered dietitians also Matanga Matai members of the professional association, New Zealand Dietetic Association (NZDA). While not directly involved with nutrition counselling, an accredited exercise physiologist (AEP), as credentialled by Exercise and Sports Science Australia (ESSA), can work in conjunction with a dietitian in the delivery of exercise for the prevention and management of chronic disease conditions.

Chapter 1: An overview of nutrition

Dietitians and nutritionists A person who calls themself a ‘dietitian’ or a ‘nutritionist’ and is a member of a relevant dietetics or nutrition professional organisation has the educational background necessary to deliver reliable nutrition advice. Dietitians usually study for a minimum of four to five years at university (includes a practical component of at least 6 months’ practice in clinical nutrition, medical nutrition therapy, community nutrition and food service management) and learn how to apply nutrition information to a range of individuals and medical conditions to improve health. This is compared with someone who is professionally recognised as a nutritionist, such as a registered nutritionist, which is the credentialling scheme overseen by the Nutrition Society

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of Australia. In New Zealand, individuals with relevant qualifications can apply for professional registration through the New Zealand Register of Nutritionists administered by the Nutrition Society of New Zealand. Nutritionists may work in a number of roles, including research, nutrition consultants and advisers public health and health promotion officers, community development officers, quality and nutrition coordinators, food technologists, media spokespeople and more. A person with a dietetics qualification could also work professionally as a nutritionist, though someone with a nutrition qualification would not be able to work professionally in all the areas covered by a dietitian. Public health nutritionists who work in government-funded agencies play a key role in delivering

HOW TO: FIND CREDIBLE SOURCES OF NUTRITION INFORMATION Government agencies, volunteer associations, consumer groups and professional organisations provide consumers with reliable health and nutrition information. Credible sources of nutrition information include: › nutrition and food science departments at universities › government health agencies, such as: › Australian Government Department of Health: http://www.health.gov.au › National Health and Medical Research Council: http://www.nhmrc.gov.au › New Zealand Ministry of Health: https://www.health.govt.nz › Therapeutic Goods Administration: http://www.tga.gov.au › non-government health agencies, such as: › Cancer Council: http://www.cancercouncil.com.au › Cancer Society of New Zealand: http://www.cancernz.org.nz › Diabetes Australia: http://www.diabetesaustralia.com.au › Diabetes New Zealand: https://www.diabetes.org.nz › Heart Foundation: http://www.heartfoundation.org.au › National Heart Foundation of New Zealand: https://www.heartfoundation.org.nz › Nutrition Society of Australia: https://www.nsa.asn.au › Nutrition Society of New Zealand: https://www.nutritionsociety.ac.nz › reputable consumer groups, such as: › Choice: http://www.choice.com.au › Consumer Affairs New Zealand: http://www.consumeraffairs.govt.nz › International Food Information Council: http://www.ific.org › professional health organisations, such as: › Dietitians Australia: https://dietitiansaustralia.org.au › New Zealand Dietetic Association: http://www.dietitians.org.nz › Australian Medical Association: http://www.ama.com.au › journals, such as: › American Journal of Clinical Nutrition: https://academic.oup.com/ajcn › British Medical Journal: http://www.bmj.com › Journal of Human Nutrition and Dietetics: https://onlinelibrary.wiley.com/ journal/1365277x › New England Journal of Medicine: http://www.nejm.org › Nutrition & Dietetics: https://onlinelibrary.wiley.com/journal/17470080 › Nutrition Reviews: https://academic.oup.com/nutritionreviews

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Understanding Nutrition

nutrition services to people in the community. Among their many roles, public health nutritionists help plan, coordinate and evaluate nutrition health-promotion programs; act as consultants to other agencies; and manage finances.

Identifying fake credentials In contrast to dietitians, thousands of people obtain fake nutrition degrees and claim to be nutrition consultants or doctors of ‘nutrimedicine’. These and other such titles may sound meaningful, but most of these people lack the established credentials and training of a registered nutritionist or DA- or NZDB-recognised dietitian. If you look closely, you can see signs of their fake expertise. Consider educational background, for example. The minimum standards of education for a dietitian specify a Bachelor of Science (BSc) degree in nutrition and/ or dietetics or relevant postgraduate training in dietetics from an accredited university. Such a degree generally requires four to five years of study. In contrast, a fake nutrition expert may display a degree from a six-month correspondence course. Such a ‘degree’ simply falls

short. In some cases, businesses posing as legitimate correspondence schools offer even less – they sell certificates to anyone who pays the fees. To obtain these ‘degrees’, a candidate need not attend any classes, read any books or pass any examinations. Knowing the qualifications of someone who provides nutrition information can help you determine whether that person’s advice might be harmful or helpful. Do not be afraid to ask for credentials. The ‘How to’ box, ‘Find credible sources of information’, lists credible sources of nutrition information.

Red flags of nutrition quackery Figure H1.2 features eight red flags consumers can use to identify nutrition misinformation. Sales of unproven and dangerous products have always been a concern, but the internet now provides merchants with an easy and inexpensive way to reach millions of customers around the world. Because of the difficulty in regulating the internet, fraudulent and illegal sales of medical products have hit a bonanza. As is the case with the air, no-one owns the internet; similarly, no-one has control over

FIGURE H1.2 Red flags of nutrition quackery

Satisfaction guaranteed

One product does it all

Time tested or newfound treatment

Marketers may make generous promises, but consumers won’t be able to collect on them.

No one product can possibly treat such a diverse array of conditions.

Such findings would be widely publicised and accepted by health professionals.

Paranoid accusations And this product’s company doesn’t want money? At least the drug company has scientific research proving the safety and effectiveness of its products.

Quick and easy fixes Even proven treatments take time to be effective.

Personal testimonials Hearsay is the weakest form of evidence.

Natural Natural is not necessarily better or safer; any product that is strong enough to be effective is strong enough to cause side effects.

Meaningless medical jargon Phony terms hide the lack of scientific proof.

Chapter 1: An overview of nutrition

pollution. Countries have different laws regarding sales of drugs, dietary supplements and other health products, but applying these laws to the internet marketplace is almost impossible. Even if illegal activities could be defined and identified, finding the person responsible for a particular website is not always possible. Websites can open and close in a blink of a cursor. Now more than ever, consumers

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must heed the caution, ‘Buyer beware’. In summary, when you hear nutrition news, consider its source. Ask yourself these two questions: Is the person providing the information qualified to speak on nutrition? Is the information based on valid scientific research? If not, find a better source. After all, your health depends on it.

HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1

How would you judge the accuracy or validity of nutrition information?

2

You have just received a forwarded email from a friend warning that the artificial sweetener aspartame is a TOXIN that causes muscle spasms, leg numbness, stomach cramps, vertigo, dizziness, headaches, tinnitus, joint pain, depression, anxiety, slurred speech, blurred vision, and memory loss. It goes on

to say that this DEADLY POISON causes blindness, multiple sclerosis, brain tumours, and cancer! The message alleges that aspartame remains on the market because of a conspiracy between FSANZ and the manufacturer to keep these dangers hidden from the public. How can you determine whether these claims are legitimate warnings or an irresponsible hoax?

NUTRITION ON THE NET •

•

•

•

Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand at http://www.foodstandards. gov.au/science/monitoringnutrients/pages/default. aspx Find an accredited practising dietitian in your area by consulting the Dietitians Australia website; also find out which nutrition and dietetics courses are accredited by the association: https:// dietitiansaustralia.org.au Learn about the Registered Nutritionist program at the Nutrition Society of Australia: http://www.nsa. asn.au Read about the professional registration of nutritionists in New Zealand: http://www. nutritionsociety.ac.nz/registration

•

• • • •

For foods commonly eaten in New Zealand, you can analyse their nutrient content from the database maintained by Plant and Food New Zealand: http://www.foodcomposition.co.nz Learn more about quackery from Stephen Barrett’s Quackwatch: http://www.quackwatch.org Visit the National Council against Health Fraud: http://www.ncahf.org Check out health-related hoaxes and urban legends: http://www.urbanlegends.about.com Find reliable research articles: https://pubmed.ncbi. nlm.nih.gov

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REFERENCES CHAPTER 1

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3

4

5

6

7

8

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L. Hwang and co-authors, New insight into human sweet taste: A genome-wide association study of the perception and intake of sweet substances, American Journal of Clinical Nutrition 109 (2019): 1724–1737. C. Smith and co-authors, Secular changes in intakes of foods among New Zealand adults from 1997 to 2008/09, Public Health Nutrition (2015): doi: 10.1017/S1368980015000890 S. L. Johnson, Developmental and environmental influences on young children’s vegetable preferences and consumption, Advances in Nutrition 7 (2016): 220S–213S. L. Schnabel and co-authors, Association between ultraprocessed food consumption and risk of mortality among middle-aged adults in France, JAMA Internal Medicine 179 (2019): 490–498. M. M. Lane and co-authors, Ultraprocessed food and chronic noncommunicable diseases: A systematic review and meta analysis of 43 observational studies, Obesity Reviews 9 (2020): doi: 10.1111/ obr.13146 M. B. Katan and co-authors, Which are the greatest recent discoveries and the greatest future challenges in nutrition? European Journal of Clinical Nutrition 63 (2009): 2–10. J. P. A. Ioannidis, The challenge of reforming nutritional epidemiologic research, Journal of the American Medical Association 320 (2018): 969–970. J. P. A. Ioannidis and J. F. Trepanowski, Disclosures in nutrition research: Why it is different, Journal of the American Medical Association 319 (2018): 547–548. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health

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11

12

13 14

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(New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). Department of Community Services and Health, National dietary survey of adults, 1983. No. 2. Nutrient intakes, Canberra: AGPS (1987); Department of Community Services and Health, National dietary survey of schoolchildren (10–15 years): 1985. No. 2. Nutrient intakes, Canberra: AGPS (1989); Australian Bureau of Statistics, National Nutrition Survey: Nutrient intakes and physical measurements, Australia, 1995, ABS Catalogue Number 4805.0, Canberra: ABS (1998); Australian Bureau of Statistics, National health survey: first results, 2017–2018, ABS Catalogue Number 4364.0.55.001, Canberra: ABS (2018). New Zealand Ministry of Health, Nutrition Survey, available at http://www.health.govt.nz/nz-health-statistics/national-collectionsand-surveys/surveys/current-recent-surveys/nutrition-survey New Zealand Ministry of Health, New Zealand Nutrition Survey, available at https://www.health.govt.nz/nz-health-statistics/nationalcollections-and-surveys/surveys/new-zealand-health-survey New Zealand Ministry of Health, Mortality web tool, available at https://www.health.govt.nz/publication/mortality-web-tool Australian Institute of Health and Welfare, Australian Burden of Disease Study: Impact and causes of illness and death in Australia 2011 (2016). A. Fardet and Y. Boirie, Associations between food and beverage groups and major diet-related chronic diseases: An exhaustive review of pooled/meta-analyses and systematic reviews, Nutrition Reviews 72 (2014): 741–762.

HIGHLIGHT 1 2

S. Rowe and N. Alexander, On post-truth, fake news, and trust, Nutrition Today 52 (2017): 179–182. C. Korownyk and co-authors, Televised medical talk shows – What they recommend and the evidence to support their recommendations: A prospective observational study, British Medical Journal 349 (2014): doi 10.1136/bmj.g7346

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M. Adamski and co-authors, Are doctors nutritionists? What is the role of doctors in providing nutrition advice? Nutrition Bulletin 43 (2018): 147–152.

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CHAPTER

2

PLANNING A HEALTHY DIET Nutrition in your life

You make food choices – deciding what to eat and how much to eat – more than 1000 times every year. We eat so frequently that it is easy to choose a meal or snack without giving any thought to its nutrient contributions or health consequences. Even when we want to make healthy choices, we may not know which foods to select or how much to consume. With a few tools and tips, you can learn to plan a healthy diet. PUTTING COMMON SENSE TO THE TEST Circle your answer

T F The concept of nutrient density means eating more kilojoules to get more nutrients. T F Dietary guidelines prescribe a set diet. T F Frozen and canned vegetables are not a suitable alternative to fresh varieties. T F  The suggested serving size on food labels is often the same as the recommended serving

in the Australian Guide to Healthy Eating.

T F Food companies can put anything they like on their food labels.

LEARNING OBJECTIVES 2.1 Explain how each of the diet-planning principles can be used to plan a healthy diet. 2.2 Use dietary guidelines to put a diet plan into action and recognise the major nutrients provided by each food group.

2.3 Compare the information on food labels to make selections that meet specific dietary and health goals.

Lemons contain a high amount of vitamin C, soluble fibre, and plant compounds that give them a number of health benefits

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Chapter 1 explained that the body’s many activities are supported by the nutrients delivered by the foods we eat. Food choices made over years influence the body’s health, with consistently poor choices increasing the risks of developing chronic disease in later life. This chapter shows how we can choose from the tens of thousands of available foods to create a diet that supports health. Most foods provide several nutrients, so wise diet planning involves selecting a combination of foods that deliver a variety of nutrients. This chapter begins by introducing the diet-planning principles and dietary guidelines that assist in selecting foods that deliver nutrients with the right amount of energy (kilojoules) for people.

2.1  Principles and guidelines Diet-planning principles: • Adequacy • Balance • Energy (kJ) Control • Nutrient Density • Moderation • Variety

How well you nourish yourself does not depend on the selection of any one food or meal. It depends on the selection of many different foods at numerous meals over days, months and years. Diet-planning principles and dietary guidelines are key concepts to keep in mind whenever you are selecting foods – whether shopping at the supermarket, choosing from a menu or preparing a home-cooked meal.

Diet-planning principles Qualified nutrition professionals use a variety of guidelines to plan diets for people. Whatever guideline or combination of guidelines they use, they keep in mind the six basic diet-planning principles listed in the margin.

Shutterstock.com/nadianb

Adequacy

To ensure an adequate and balanced diet, eat a variety of foods daily and choose different foods from each food group.

Adequacy means that the diet provides sufficient energy and enough of all the nutrients to meet the needs of healthy people. Take the essential nutrient iron, for example. Because the body uses some iron each day, we need to replace it by eating foods that contain iron. A diet that fails to provide enough iron-rich foods may result in symptoms of iron-deficiency anaemia, whereby a person may feel weak, tired, have frequent headaches, and find that even the smallest amount of activity brings fatigue. To prevent these deficiency symptoms, we must include foods that supply adequate iron. This is true for all the other essential nutrients introduced in Chapter 1.

Balance

Balance in the diet helps to ensure adequacy.

The art of balancing our diet involves consuming enough – but not too much – of foods from each food group. The essential minerals calcium and iron, taken together, illustrate the importance of dietary balance. Meats, fish and poultry are rich in iron but poor in calcium. Conversely, milk and milk products are rich in calcium but poor in iron. Eat some meat or meat alternatives for iron; drink some milk or fortified milk products for calcium; and save some space for other foods, too because a diet consisting of milk and meat alone would not be adequate. For other nutrients, people need whole grains, vegetables and fruits.

Energy (kilojoule) control Designing an adequate diet within a reasonable kilojoule allowance requires careful planning. Once again, balance plays a key role. The amount of energy we consume should balance with the amount of energy we use to sustain metabolic and physical activities. Upsetting this balance leads to gains or losses in body weight. The discussions of energy balance and weight control in Chapters 8 and 9 examine this issue in more detail, but the key to kilojoule control is to select foods of high nutrient density.

Chapter 2: Planning a healthy diet

Nutrient density To eat well without overeating, select foods that provide the most nutrients for the least energy (kilojoules). Consider foods containing calcium, for example. You can get about 300 milligrams of calcium from either 40 grams of cheddar cheese or 1 cup of low-fat milk, but the cheese delivers about twice as many kilojoules as the milk. The low-fat milk, then, is twice as calcium dense as the cheddar cheese; it offers the same amount of calcium for half the kilojoules. Both foods are excellent choices for calcium adequacy alone, but to achieve adequacy while controlling kilojoules, the low-fat milk is the better choice. (Alternatively, a person could select a low-fat cheddar cheese.) The many bar graphs that appear in Chapters 10 to 13 indicate the most nutrient-dense choices. The following ‘How to’ box describes how to compare foods based on nutrient density.

HOW TO:

COMPARE FOODS BASED ON NUTRIENT DENSITY

One way to evaluate foods is simply to notice their nutrient contribution per serving: 1 cup of milk provides about 300 milligrams of calcium, and ½ cup of cooked spinach provides about 120  milligrams. Thus, a serving of milk offers 2½  times as much calcium as a serving of cooked spinach. To obtain 300 milligrams of calcium, a person could choose either 1 cup of milk or 1¼ cups of cooked spinach. Another valuable way to evaluate foods is to consider their nutrient density – their nutrient contribution per kilojoule. Low-fat milk delivers about 480 kilojoules with its 300 milligrams of calcium. To calculate the nutrient density, divide milligrams by kilojoules:

300 mg calcium = 0.6 mg per kJ 480 kJ Do the same for the cooked spinach, which provides 85 kilojoules with the 120 milligrams of calcium:

120 mg calcium = 1.4 mg per kJ 85 kJ The more milligrams per kilojoule, the greater the nutrient density. Cooked spinach is more calcium-dense than milk. It provides more calcium per kilojoule than milk, but milk offers more calcium per serving. Both approaches offer valuable information, especially when combined with a realistic appraisal. What matters most is which are you more likely to consume – 1¼ cups of cooked spinach or 1 cup of milk? You can get 300 milligrams of calcium from either, but the spinach will save you about 400 kilojoules (the savings would be even greater if you usually use whole milk). Keep in mind, too, that calcium is only one of the many nutrients that foods provide. Similar calculations for protein, for example, would show that low-fat milk provides more protein both per kilojoule and per serving than cooked spinach – that is, milk is more protein-dense. Combining variety with nutrient density helps to ensure the adequacy of all nutrients. Just as a financially responsible person pays for rent, food and clothes on a limited budget, we obtain iron, calcium and all the other essential nutrients on a limited energy allowance. Success depends on getting many nutrients for each kilojoule ‘dollar’. For example, a can of soft drink and a handful of grapes may both provide about the same number of kilojoules, but the grapes deliver many more nutrients. A person who makes nutrient-dense choices, such as fruit instead of soft drink, can meet daily nutrient needs on a lower energy budget. Such choices support good health.

Nutrient density promotes adequacy and kilojoule control.

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Understanding Nutrition

Foods that are notably low in nutrient density, such as potato chips, lollies and soft drinks, are sometimes called empty-kilojoule foods. The kilojoules these foods provide are called ‘empty’ because they deliver energy (from sugar, fat or both) with little or no protein, vitamins or minerals. The concept of nutrient density is relatively simple when examining the contributions of one nutrient to a food or diet. With respect to calcium, milk ranks high and meats rank low; but with respect to iron, meats rank high and milk ranks low. It is a more complex task to determine which food is more nutritious. For that, we need to consider several nutrients – including both nutrients to encourage (protein, fibre, vitamins and minerals) and those to limit (saturated fats, added sugars, sodium). Ranking foods based on their overall nutrient composition is known as nutrient profiling. Researchers have yet to agree on the best system to rate foods based on nutrient profiling, but when they do, nutrient profiling will be most helpful in identifying nutritious foods and planning healthy diets.1

Moderation Moderation contributes to adequacy, balance and energy control.

Foods that are rich in fat and sugar provide enjoyment and energy but relatively few nutrients. In addition, they promote weight gain when eaten in excess. When we practise moderation we eat such foods occasionally and regularly select foods low in saturated fats and added sugars, a practice that automatically improves nutrient density. Returning to the example of cheddar cheese versus low-fat milk, the low-fat milk not only offers the same amount of calcium for less energy, but also contains far less fat than the cheese.

Variety

PUTTING COMMON SENSE TO THE TEST

The concept of nutrient density means eating more kilojoules to get more nutrients. FALSE

A diet may have all the virtues just described and still lack variety if a person eats the same foods day after day. People should select foods from each of the food groups daily and vary their choices within each food group from day to day. Different foods within the same group contain a different variety of nutrients. Among the fruits, for example, strawberries are especially rich in vitamin C while apricots are rich in vitamin A. Variety improves nutrient adequacy.2 Additionally, no food is guaranteed to be entirely free of substances that, in excess, could be harmful. The strawberries might contain trace amounts of one contaminant, the apricots another. By alternating fruit choices, a person will ingest very little of either contaminant. (Contamination of foods is discussed in Chapter 19.) Finally, as the adage goes, variety is the spice of life. A person who eats beans frequently can enjoy pinto beans in Mexican burritos today, chickpeas in Greek salad tomorrow, and baked beans on toast on the weekend. Eating nutritious meals need never be boring.

Dietary guidelines in Australia and New Zealand What should a person eat to stay healthy? The answers can be found in the Australian Dietary Guidelines3 and the Eating and Activity Guidelines for New Zealand Adults.4 These guidelines use science-based evidence to provide information about healthy food choices. The use of the guidelines promotes health and minimises the risk of diet-related diseases for Australians, both at an individual and a population level. Table 2.1 presents the Australian Dietary Guidelines, which, when used in conjunction with the Australian Guide to Healthy Eating (discussed later in this chapter), points the way towards better health. Table 2.2 presents New Zealand’s Eating and Activity Guidelines for New Zealand Adults.

Chapter 2: Planning a healthy diet

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TABLE 2.1  The Australian Dietary Guidelines GUIDELINE 1: TO ACHIEVE AND MAINTAIN A HEALTHY WEIGHT, BE PHYSICALLY ACTIVE AND CHOOSE AMOUNTS OF NUTRITIOUS FOOD AND DRINKS TO MEET YOUR ENERGY NEEDS • Children and adolescents should eat sufficient nutritious foods to grow and develop normally. They should be physically active every day and their growth should be checked regularly •  Older people should eat nutritious foods and keep physically active to help maintain muscle strength and a healthy weight GUIDELINE 2: ENJOY A WIDE VARIETY OF NUTRITIOUS FOODS FROM THESE FIVE GROUPS EVERY DAY •  Plenty of vegetables, including different types and colours, and legumes/beans • Fruit • Grain (cereal) foods, mostly wholegrain and/or high cereal fibre varieties, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley •  Lean meats and poultry, fish, eggs, tofu, nuts and seeds, and legumes/ beans • Milk, yoghurt, cheese and/or their alternatives, mostly reduced fat (reduced fat milks are not suitable for children under the age of two years) • Drink plenty of water GUIDELINE 3: LIMIT INTAKE OF FOODS CONTAINING SATURATED FAT, ADDED SALT, ADDED SUGARS a Limit intake of foods high in saturated fat, such as many biscuits, cakes, pastries, pies, processed meats, commercial burgers, pizza, fried foods, potato chips, crisps and other savoury snacks • Replace high fat foods which contain predominantly saturated fats, such as butter, cream, cooking margarine, coconut and palm oil with foods that contain predominantly polyunsaturated and mono-unsaturated fats, such as oils, spreads, nut butters/pastes and avocado •  Low fat diets are not suitable for children under the age of two years b  Limit intake of foods and drinks containing added salt •  Read labels to choose lower sodium options among similar foods •  Do not add salt to foods in cooking or at the table c Limit intake of foods and drinks containing added sugars, such as confectionery, sugar-sweetened soft drinks and cordials, fruit drinks, vitamin waters, energy and sports drinks d If you choose to drink alcohol, limit intake. For women who are pregnant, planning a pregnancy or breastfeeding, not drinking alcohol is the safest option GUIDELINE 4: ENCOURAGE, SUPPORT AND PROMOTE BREASTFEEDING GUIDELINE 5: CARE FOR YOUR FOOD; PREPARE AND STORE IT SAFELY © National Health and Medical Research Council. Eat for Health: Australian Dietary Guidelines, (2013): 5. © Commonwealth of Australia 2016 reproduced by permission. CC BY 4.0 International Licence. (https://www.eatforhealth.gov.au/copyright-information).

TABLE 2.2   Eating and Activity Guidelines for New Zealand Adults EATING STATEMENTS 1  Enjoy a variety of nutritious foods every day, including: •  plenty of vegetables and fruit •  grain foods, mostly whole grain and those naturally high in fibre •  some milk and milk products, mostly low and reduced fat •  some legumes, nuts, seeds, fish and other seafood, eggs, poultry (e.g. chicken) and/or red meat* with the fat removed * If choosing red meat, eat less than 500 g of cooked red meat a week 2  Choose and/or prepare foods and drink: •  with unsaturated fats instead of saturated fats •  that are low in salt (sodium); if using salt, choose iodised salt •  with little or no added sugar •  that are mostly ‘whole’ and less processed 3  Make plain water your first choice over other drinks 4  Any alcohol consumption is risky, so if you drink alcohol, keep your intake low. Stop drinking alcohol if you could be pregnant, are pregnant or are trying to get pregnant. When breastfeeding, it is best to be alcohol-free 5  Buy or gather, prepare, cook and store food in ways that keep it safe to eat. Take extra care to protect yourself from foodborne illness if you are pregnant 6 Encourage, support and promote breastfeeding

TABLE 2.2

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Understanding Nutrition

ACTIVITY STATEMENTS 1  Sit less, move more! Break up long periods of sitting 2 Do at least two-and-a-half hours of moderate or one-and-a-quarter hours of vigorous physical activity spread throughout the week. Pregnant women should aim to do two-and-a-half hours of moderate-intensity physical activity spread over at least three days per week (preferably some activity every day) 3 For extra health benefits, aim for 5 hours of moderate or two-and-a-half hours of vigorous physical activity spread throughout the week. Pregnant women should seek advice from a healthcare professional if competing in events or if exercising significantly more than Activity Statement 2 4 Do muscle strengthening activities on at least two days each week. Pregnant women may also benefit from doing stretching and pelvic floor muscle training daily 5 Doing some physical activity is better than doing none. All pregnant women without serious health conditions should be regularly physically active through a variety of aerobic and resistance activities BODY WEIGHT STATEMENT Making good choices about what you eat and drink and being physically active are important to achieve and maintain a healthy body weight. Being a healthy weight: •  helps you to stay active and well •  reduces your risk of developing type 2 diabetes, heart disease and some cancers If you are struggling to maintain a healthy weight, see your doctor and/or your community healthcare provider When you are pregnant, talk to your midwife or doctor about the right amount of weight to gain during pregnancy. This amount is different for each person Adapted from Ministry of Health, 2020. Eating and Activity Guidelines for New Zealand Adults. Wellington: Ministry of Health (2020). CC BY 4.0 International License. (https://www.health.govt.nz/about-site/copyright

Some people might wonder why dietary guidelines include recommendations for physical activity. Generally, most people who maintain a healthy body weight eat well and exercise, engaging in moderately intense physical activity most days.

• breads, cereals, rice, pasta, noodles • vegetables and legumes • fruit • milk, yoghurt and cheese • meat, fish, poultry, eggs, nuts, legumes. (Note that in Australia, legumes are in two groups. Also in New Zealand there are four food groups due to vegetables and fruit being one group).

REVIEW IT

The five food groups are:

A well-planned diet delivers adequate nutrients, a balanced variety of nutrients and an appropriate amount of energy. It includes nutrient-dense foods, is moderate in substances that can be detrimental to health and is varied in its selections. The Australian Dietary Guidelines and the Eating and Activity Guidelines for New Zealand Adults apply these principles, offering practical advice on how to eat for good health.

2.2  Diet-planning guides

To plan a diet that achieves all the dietary ideals just outlined, we need tools as well as knowledge. Among the most widely used tools for diet planning are food group plans that build a diet from groups of foods that are similar in nutrient content. Thus, each group represents a set of nutrients that differ somewhat from the nutrients supplied by the other groups. Selecting foods from each of the groups allows us to create an adequate and balanced diet.

The Australian Guide to Healthy Eating The Australian Dietary Guidelines encourage people to eat a balanced diet. The Department of Health has developed the Australian Guide to Healthy Eating. Figure 2.1 combines recommendations from the Australian Guide to Healthy Eating with those of the Australian Dietary Guidelines. It assigns foods to five major groups and recommends daily amounts of foods from each group to meet nutrient needs. In addition to presenting the food groups, the figure lists the most notable nutrients of each group, the serving equivalents and the foods within each group sorted by nutrient density. Chapter 16 provides a food guide for young children.

Chapter 2: Planning a healthy diet

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FIGURE 2.1   Australian Dietary Guidelines: eat a wide variety of nutritious foods from these five groups every day

Shutterstock.com/Romariolen

FRUITS Fruits contribute folate, vitamin A, vitamin C, potassium and fibre. • 1 medium piece (150 g) of fruit (apple, banana, orange, pear) • 2 small pieces (150 g) of fruit (apricots, kiwifruit, plums) • 1 cup (150 g) diced pieces or canned fruit • 1½ tablespoons sultanas, 4 dried apricot halves • ½ cup (125 mL) fruit juice

These serving sizes supply about 300 kJ each. Examples: Apples, apricots, avocados, bananas, blueberries, rockmelon, cherries,grapefruit, grapes, guava, kiwifruit, mango, oranges, papaya, peaches, pears, pineapples, plums, raspberries, strawberries, watermelon, dried fruit (dates, figs, raisins), unsweetened juices

Shutterstock.com/Katrinshine

VEGETABLES AND LEGUMES/ BEANS Vegetables and legumes/beans contribute folate, vitamin A, vitamin C, vitamin K, vitamin E, magnesium, potassium and fibre. •  ½ cup (75 g) cooked vegetables • ½ cup (75 g) cooked dried beans, peas or lentils •  1 cup salad vegetables •  1 small potato These serving sizes supply about 75–250 kJ each.

Shutterstock.com/Hurst Photo

iStock.com/ranplett

Examples: Dark green vegetables: Broccoli and leafy greens such as spinach, bok choy, lettuce, kale and silverbeet GRAINS (CEREAL) FOODS Grain foods contribute folate, niacin,riboflavin, thiamin, iron, magnesium, selenium and fibre • 1 slice (40 g) bread, ½ medium bread roll • ½ cup (90 g) cooked rice, pasta, noodles • ½ cup (115 g) cooked porridge, ⅔ cup (30 g) cereal flakes or readyto-eat cereal

LEAN MEAT AND POULTRY, FISH, EGGS, NUTS AND SEEDS AND LEGUMES/BEANS

Meat, poultry, fish and eggs contribute protein, niacin, thiamin, vitamin B6, vitamin B12, iron, magnesium, potassium and zinc; legumes and nuts are notable for their protein, folate, thiamin, vitamin E, iron, magnesium, potassium, zinc and fibre. Care needs to be taken to ensure an adequate intake of iron, zinc and vitamin B12 with vegetarian and vegan diets. • 65 g cooked meat: ½ cup of lean mince, 2 small chops, 2 slices of roast meat •  80 g of cooked poultry

Orange and deep yellow vegetables: Carrots, pumpkin, sweet potatoes and squash Legumes: Black beans, blackeyed peas, chickpeas, kidney beans, lentils, navy beans, pinto beans, soybeans and soy products such as tofu, and split peas Starchy vegetables: Potatoes, corn and lima beans Other vegetables: Artichokes, asparagus, bean sprouts, brussels sprouts, cabbages, cauliflower, celery, cucumbers, eggplant, green beans, mushrooms, okra, onions, peppers, snow peas, tomatoes and zucchini •  ¼ cup flour • 1 crumpet (60 g) or 1 small English muffin (35 g) These serving sizes supply about 400 kJ each.

Examples: Whole grains (barley, brown rice, buckwheat, bulgur, millet, oats, rye, wheat) and wholegrain breads, cereals, crackers and pastas • 1 cup (170 g) cooked (dried) beans, lentils, chickpeas, split peas and canned beans •  100 g cooked fish fillet •  2 large eggs (120 g) • 30 g nuts or nut/seed paste These serving sizes supply about 600–850 kJ each. Examples: Poultry (no skin), fish, shellfish, legumes, eggs, lean meat (fattrimmed beef, game, ham, lamb, pork); lowfat tofu, tempeh, peanut butter, nuts (almonds, peanuts, pistachios, walnuts) or seeds (flaxseeds, pumpkin seeds, sunflower seeds)

Shutterstock.com/Alexander Prokopenko

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Understanding Nutrition

MILK, YOGHURT, CHEESE AND/ OR THEIR ALTERNATIVES Dairy foods contribute protein, riboflavin, vitamin B12, calcium, magnesium, potassium and, when fortified, vitamin D. • 1 cup (250 mL) fresh, long-life or reconstituted dried milk •  1 cup (250 mL) soy milk •  ½ cup (125 mL) evaporated milk •  2 slices (40 g) cheese

Shutterstock.com/JPC-PROD

FATS AND OILS – USE SMALL AMOUNTS Limit intake of foods and drinks containing saturated and trans fats. Fats and oils contribute vitamin E and essential fatty acids (see Chapter 5), along with abundant kilojoules. Choose polyunsaturated and monounsaturated margarines and oils.

Cengage Learning/Ronald Chung

DISCRETIONARY FOODS AND BEVERAGES Limit intake of foods and drinks containing added salt, added sugars and alcohol. Discretionary foods should only be chosen sometimes and in small amounts. Most people can eat small amounts of discretionary foods as part of a healthy diet. A healthier alternative is to eat more food from the five food groups most of the time. Example servings of discretionary foods (providing about 600 kJ each) include: •  1 (40 g) doughnut •  4 (35 g) plain sweet biscuits •  1 slice (40 g) cake

•  1 small carton (200 g) yoghurt •  1 cup (250 mL) custard These serving sizes supply about 375–730 kJ each (custard, 1100 kJ). Examples: Fat-free milk and fat-free milk products such as buttermilk, cheeses, cottage cheese, yoghurt; fat-free fortified soy beverage, low-fat milk and low-fat milk products such as cheeses, cottage cheese, yoghurt and custard

Examples: Sunflower oil, safflower oil, corn oil, soybean oil, olive oil, peanut oil, canola oil and margarines derived from these products; unsaturated oils that occur naturally in foods such as avocados, fatty fish, nuts, olives, seeds (flaxseeds, sesame seeds) and shellfish

•  25 g (½ small bar) chocolate • 2 tablespoons (40 g) cream, mayonnaise • 1 tablespoon (20 g) butter, margarine, oil •  200 mL wine (2 standard drinks) •  60 mL spirits (2 standard drinks) • 600 mL light beer (approximately 1½ standard drinks) • 400 mL regular beer (approximately 1½ standard drinks) •  1 can (375 mL) soft drink •  1 small packet (30 g) potato crisps •  1/3 (60 g) meat pie or pasty •  12 (60 g) hot chips •  1½ scoops (50 g scoop) ice-cream.

Adapted from National Health and Medical Research Council, Department of Health and Ageing, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2013). CC BY 4.0 International Licence (https://www.eatforhealth.gov.au/copyright-information)

Recommended amounts All food groups offer valuable nutrients, and people should select from each group daily. Table 2.3 and Table 2.4 indicate the number of serves needed from each group daily to create a healthful diet for all age groups.

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TABLE 2.3   Recommended dietary patterns for men and women

Milk, yoghurt, cheese and/or alternatives (mostly reduced fat)

Approximate number of additional serves from the five food groups or discretionary choices

19–50

6

2

6

3

2½

0–3

51–70

5½

2

6

2½

2½

0–2½

70+

5

2

4½

2½

3½

0–2½

19–50

5

2

6

2½

2½

0–2½

51–70

5

2

4

2

4

0–2½

70+

5

2

3

2

4

0–2

Pregnant

(19–50)

5

2

8½

3½

2½

0–2½

Lactating

(19–50)

7½

2

9

2½

2½

0–2½

Men

Women

Fruit

Age

Vegetables and legumes/ beans

Lean meat and poultry, fish, eggs, nuts and seeds, and legumes/beans

ADDITIONAL SERVES FOR TALLER OR MORE ACTIVE MEN AND WOMEN

Grain (cereal) foods, mostly wholegrain, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley

RECOMMENDED AVERAGE DAILY NUMBER OF SERVES FROM EACH OF THE FIVE FOOD GROUPS*

*Includes an allowance for unsaturated spreads or oils, nuts or seeds (4 serves [28−40 g] per day for men less than 70 years of age; 2 serves [14−20 g] per day for women and older men) National Health and Medical Research Council, Eat for Health Australian Dietary Guidelines Summary, p. 41. https://www.eatforhealth.gov.au/sites/default/files/ content/The%20Guidelines/n55a_australian_dietary_guidelines_summary_131014_1.pdf. © Commonwealth of Australia 2015, CC BY 3.0 Australia

TABLE 2.4   Recommended dietary patterns for children, adolescents and toddlers

Approximate number of additional serves from the five food groups or discretionary choices

ADDITIONAL SERVES FOR MORE ACTIVE, TALLER OR OLDER CHILDREN AND ADOLESCENTS Milk, yoghurt, cheese and/or alternatives (mostly reduced fat)

Lean meat and poultry, fish, eggs, nuts and seeds, and legumes/ beans

Grain (cereal) foods, mostly wholegrain, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley

Fruit

Age

Vegetables and legumes/beans

RECOMMENDED AVERAGE DAILY NUMBER OF SERVES FROM EACH OF THE FIVE FOOD GROUPS*

Toddlers

1–2

2–3

½

4

1

1–1½

–

Boys

2–3

2½

1

4

1

1½

0–1

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Understanding Nutrition

TABLE 2.4

RECOMMENDED AVERAGE DAILY NUMBER OF SERVES FROM EACH OF THE FIVE FOOD GROUPS*

Girls

ADDITIONAL SERVES FOR MORE ACTIVE, TALLER OR OLDER CHILDREN AND ADOLESCENTS

4–8

4½

1½

4

1½

2

0–2½

9–11

5

2

5

2½

2½

0–3

12–13

5½

2

6

2½

3½

0–3

14–18

5½

2

7

2½

3½

0–5

2–3

2½

1

4

1

1½

0–1

4–8

4½

1½

4

1½

1½

0–1

9–11

5

2

4

2½

3

0–3

12–13

5

2

5

2½

3½

0–2½

14–18

5

2

7

2½

3½

0–2½

Pregnant

5

2

8

3½

3½

0–3

Lactating

5½

2

9

2½

4

0–3

*Includes an allowance for unsaturated spreads or oils, nuts or seeds (½ serve [4−5 g] per day for children 2−3 years of age, 1 serve [7−10 g] per day for children 3−12 years of age; 1½ serves [11−15 g] per day for children 12−13 years, and 2 serves [14−20 g] per day for adolescents 14−18 years of age and for pregnant and lactating girls). National Health and Medical Research Council. Eat for Health Australian Dietary Guidelines Summary, p. 42. https://www.eatforhealth.gov.au/sites/default/ files/content/The%20Guidelines/n55a_australian_dietary_guidelines_summary_131014_1.pdf. © Commonwealth of Australia 2015, CC BY 3.0 Australia.

All vegetables provide an array of vitamins, fibre and the mineral potassium, but some vegetables are especially good sources of certain nutrients, and of beneficial phytochemicals – the non-nutrient compounds found in plant-derived foods that have biological activity in the body. Dark green vegetables deliver the B-group vitamin folate; orange vegetables provide vitamin A; legumes supply iron and protein; starchy vegetables contribute carbohydrate; and other vegetables fill in any gaps and add more of these same nutrients.

Notable nutrients

As shown in Figure 2.1, each food group contributes key nutrients. This provides flexibility in diet planning because a person can select any food from a food group and receive similar nutrients. For example, a person can choose milk, cheese or yoghurt and receive the same key nutrients. Because legumes contribute the same key nutrients as meats, poultry and fish (protein, iron and zinc), they are included in the same food group. For this reason, legumes are useful as meat alternatives, but they are also excellent sources of fibre and the B-group vitamin folate. To encourage frequent consumption, legumes are also included in the vegetable group. Thus, legumes count in either the vegetable group or the meat and legumes group. Generally, people who regularly eat meat, poultry and fish count legumes as a vegetable, and vegetarians or others who seldom eat meat, poultry or fish count legumes in the meat group.

Nutrient density

The Australian Guide to Healthy Eating provides a foundation for a healthy diet by emphasising nutrient-dense options within each food group. By consistently selecting nutrient-dense foods, a person can obtain all the nutrients needed and still maintain an appropriate energy balance. In contrast, eating foods that are low in nutrient density makes it difficult to get enough nutrients without exceeding energy needs and likely gaining weight. For this reason, people should select low-fat foods from each group where appropriate, and foods without added fats or sugars. For example, low-fat milk instead of whole milk, chicken without the skin instead of with the skin, steamed or boiled potatoes instead of chips, and whole fruit instead of fruit

Chapter 2: Planning a healthy diet

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juice. Oil is a notable exception: even though oil is pure fat and therefore rich in kilojoules, a small amount of oil from sources such as nuts, fish or vegetable oils is necessary every day to provide nutrients lacking from other foods. Consequently, these high-fat foods are listed among the nutrient-dense foods (see Highlight 5 to learn why).

Serving equivalents Recommended serving amounts for fruits, vegetables and milk are generally measured in cups and those for grains and meats in grams. Figure 2.1 provides equivalent measures among the foods in each group, specifying, for example, that a slice of bread or ½ cup of cooked rice is equivalent to approximately 300 kilojoules. A person using the Australian Guide to Healthy Eating can become more familiar with measured portions by determining the answers to questions such as these: What portion of a cup is a small handful of raisins? Is a ‘serving’ of mashed potatoes more or less than a half-cup? How many grams of breakfast cereal do you typically pour into the bowl? How many grams is the steak at your favourite restaurant? Figure 2.1 includes the serving sizes and equivalent amounts for foods within each group.

Vegetarian food guide Vegetarian diets rely mainly on plant foods: grains, vegetables, legumes, fruits, seeds and nuts. Some vegetarian diets include eggs, milk products or both. People who do not eat meats or milk products can still use the Australian Guide to Healthy Eating to create an adequate diet.5 The food groups are similar, and the amounts for each serving remain the same. Highlight 2 defines vegetarian terms and provides details on planning healthy vegetarian diets.

The Australian Guide to Healthy Eating circle (plate) and the Nutrition Australia Healthy Eating Pyramid As can be seen in Figure 2.2, the Australian Guide to Healthy Eating uses a circle (often referred to as a plate) to illustrate how recommendations can be implemented. Nutrition Australia explains how a healthy diet can be implemented using a pyramid. Each of these tools is a useful resource for people trying to plan healthy diets.

PUTTING COMMON SENSE TO THE TEST

Dietary guidelines prescribe a set diet. FALSE

The Australian Nutrition Foundation, Inc. http://www.nutritionaustralia.org

FIGURE 2.2  The Australian Guide to Healthy Eating circle (plate) and the Nutrition Australia Healthy Eating Pyramid

Source: National Health and Medical Research Council

For quick and easy estimates, visualise each portion as being about the size of a common object: • 1 cup fruit or vegetables = a cricket ball • ¼ cup dried fruit = a golf ball • 1 00 g of meat = a deck of cards • 1 tsp peanut butter = a marshmallow • ½  cup ice-cream = a tennis ball.

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Understanding Nutrition

Putting the plan into action Familiarising yourself with each of the food groups is the first step in diet planning. Table 2.5 shows how to use the Australian Guide to Healthy Eating to plan an 8700-kilojoule diet. The amounts listed from each of the food groups are assigned to meals and snacks as an example only.

TABLE 2.5   Example of a diet planned according to the Australian Guide to Healthy Eating FOOD GROUP

AMOUNTS

BREAKFAST

SNACK

Fruits

2 serves

1 small piece

1 small piece

Vegetables and legumes

6 serves

Breads and cereals

6 serves

1−2 serves of breakfast cereal

Dairy foods

2½ serves

glass of milk

Meat and legumes

2–3 serves

Discretionary foods

up to 2½ serves

LUNCH

SNACK

DINNER AND DESSERT

1 medium piece

½ cup salad vegetables

1 cup salad vegetables

2 potatoes, ½ cup of legumes, 1 cup of cooked vegetables

1 serve of dry crackers

2 slices of bread

1 medium bread roll

1 slice of cheese

1 serve of yoghurt

Small tin of tuna

100 g of lean red meat

1 serve margarine

25 g chocolate bar

We can begin to fill in the plan with real foods to create an eating pattern to sustain good health. For example, breakfast calls for 30 grams of grain, ½ cup fruit and 1 cup of milk. We might select a bowl of cereal with banana slices and milk: • 1 cup cereal = 30 grams grain • 1 small banana = ½ cup fruit • 1 cup fat-free milk = 1 cup milk. We can then continue to create a diet plan by establishing healthy eating patterns for lunch, dinner and other snacks. As you can see, we all make countless food-related decisions daily – whether we have a plan or not. Following a plan, such as the Australian Guide to Healthy Eating, that incorporates health recommendations and diet-planning principles helps a person make wise decisions.

From guidelines to the shopping trolley Dietary recommendations emphasise nutrient-rich foods such as whole grains, fruits, vegetables, lean meats, fish, poultry and low-fat milk products. You can design such a diet for yourself, but how do you begin? Start with the foods you enjoy eating. Then try to make improvements, little by little where needed. When shopping, think of the food groups and choose nutrient-dense foods within each group. Be aware that many of the 50  000 food options available today are processed foods that have lost valuable nutrients and have had sugar, fat and salt added as they were transformed from farm-fresh foods to those found in the bags, boxes and cans that line supermarket shelves. Their value in the diet depends on the starting food and how it was prepared or processed. Sometimes these foods have been fortified to improve their nutrient contents. Refer to the ‘Current research in nutrition’ box in Chapter 1 for the risks associated with highly processed foods.

Chapter 2: Planning a healthy diet

Breads and cereals

When shopping for bread and cereal products, you may find them described as refined, enriched or wholegrain. These terms refer to the milling process and the making of grain products, and they have different nutrition implications (see Figure 2.3). Refined foods may have lost many nutrients during processing, enriched products may have had some nutrients (generally vitamins and minerals) added back and wholegrain products may be rich in fibre and all the nutrients found in the original grain. Wholegrain products support good health and should comprise the majority of choices within this food group. Ready-to-eat breakfast cereals are the most commonly fortified foods on the market. A fortified food has had nutrients added during processing, but the added nutrients may not have been present in the original product. Caution should be used when selecting breakfast cereals made from refined grains and fortified with vitamins and minerals as, while these may appear a healthy choice because of the fortification, they may fail to provide the full spectrum of nutrients that a wholegrain food or a mixture of such foods might provide. Wholegrain breads generally provide more nutrition than other breads. However, due to legislation implemented through Food Standards Australia New Zealand (FSANZ), Australian flour millers are required to add the B-group vitamin folic acid to all bread flours, except for flour to be used in breads listed as ‘organic’. The mandatory fortification of bread flour was implemented due to a significant public health need as folic acid is important in the healthy development of babies in early pregnancy to reduce the risk of neural tube defects. In New Zealand, a voluntary fortification standard for fortifying up to 50 per cent of packaged sliced bread has been in place, with all non-organic wheat flour used for bread making required to be fortified with folic acid from mid-2023.

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Grain-enrichment nutrients include: • iron • thiamine • riboflavin • niacin • folate.

AUSTRALIAN DIETARY GUIDELINES 2013 ---------------

Enjoy a wide variety of nutritious foods every day, including milk, plenty of fruits and vegetables of different types and colours and legumes/beans.

FIGURE 2.3   A wheat plant

The protective coating of bran around the kernel of grain is rich in nutrients and fibre. The endosperm contains starch and proteins. The germ is the seed that grows into a wheat plant, so it is especially rich in vitamins and minerals to support new life. The outer husk (or chaff) is the inedible part of a grain.

Common types of flour are: refined flour: finely ground endosperm that is usually enriched with nutrients and bleached for whiteness; sometimes called white flour. wheat flour: any flour made from the endosperm of the wheat kernel. whole-wheat flour: any flour made from the entire wheat kernel. The difference between white flour and white wheat is noteworthy. Typically, white flour refers to refined flour (as defined above). Most flour – whether refined, white, or whole wheat – is made from red wheat. Wholegrain products made from red wheat are typically brown and full-flavoured. To capture the health benefits of whole grains for people who prefer white bread, manufacturers use an albino variety of wheat called white wheat. Wholegrain products made from white wheat provide the nutrients and fibre of a whole grain with a light colour and natural sweetness. Read labels carefully – white bread is a wholegrain product only if it is made from whole white wheat.

© Thomas Harm & Tom Peterson/Quest Photographic, Inc.

Wholegrain products contain much of the germ and bran, as well as the endosperm; that is why they are so nutritious. Refined grain products contain only the endosperm. Even with nutrients added back, they are not as nutritious as wholegrain products.

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Understanding Nutrition

Shutterstock.com/gpointstudio

FIGURE 2.4   Go for 2 fruit and 5 veg

When shopping for bread, look for the descriptive words wholegrain or whole wheat and check the fibre content on the nutrition information panel of the label – the more fibre, the more likely the bread is to be a wholegrain product.

PUTTING COMMON SENSE TO THE TEST

Frozen and canned vegetables are not a suitable alternative to fresh varieties. FALSE

Legumes comprise a variety of beans and peas including: • adzuki beans • black beans • black-eyed beans • chickpeas • fava beans • kidney beans • lentils • lima beans • navy beans • peanuts • pinto beans • soybeans • split peas.

http://www.gofor2and5.com.au/ © State of Western Australia 2016. Reproduced with permission.

Vegetables Choose vegetables regularly, either fresh, canned or frozen (taking care to avoid added salt, sugar and fat), especially dark green leafy and yellow-orange vegetables, such as spinach, broccoli and sweet potatoes (see Figure 2.4). Cooked or raw, vegetables are good sources of vitamins, minerals and fibre. Frozen and canned vegetables without added salt are acceptable alternatives to fresh varieties. To control fat, energy and sodium intakes, limit butter and salt on vegetables. Choose often from the variety of legumes available. They are an economical, low-fat, nutrient- and fibre-rich food choice.

Fruit Choose fresh fruits often. Frozen, dried and canned fruits without added sugar are acceptable alternatives to fresh but be cautious as these can be a concentrated form of energy and may contain less fibre. Fruits supply valuable vitamins, minerals, fibre and phytochemicals. They can add flavours, colours and textures to meals, and their natural sweetness makes them enjoyable as snacks or desserts. Fruit juices are healthy beverages but contain little dietary fibre compared with whole fruits. Whole fruits satisfy the appetite better than juices, thereby helping people to limit kilojoule intake. For people who need extra kilojoules, however, juices are a good choice. Be aware that sweetened fruit ‘drinks’ contain mostly water, sugar and a little juice for flavour. Some may have been fortified with vitamin C or calcium but lack any other significant nutritional value.

Meat, fish and poultry Meat, fish and poultry provide essential minerals, such as iron and zinc, and abundant B-group vitamins as well as protein. To buy and prepare these foods without excess energy, fat

1998 PhotoDisc, Inc.

Combining legumes with foods from other food groups creates delicious meals.

Shutterstock.com/Ffolas

Add rice to red beans for a hearty meal.

Shutterstock.com/Sea Wave

Enjoy a Greek salad topped with chickpeas for a little ethnic diversity.

iStockphoto/Raul Taborda

A bit of meat and lots of spices turn kidney beans into chilli con carne.

Chapter 2: Planning a healthy diet

and sodium takes a little knowledge and planning. When shopping, choose fish, poultry and lean cuts of pork or red meat. In general, 120 grams of raw meat is equal to about 100 grams of cooked meat. Some examples of 100-gram portions of meat include 1 medium lean pork chop, ½ chicken breast with skin removed or 1 steak about the size of a deck of cards. To keep fat intake moderate try to bake, roast, grill or braise meats (limit frying in fat); remove the skin from poultry before or after cooking; trim visible fat before cooking; and drain fat after cooking. Chapter 5 offers many additional strategies for moderating fat intake.

AUSTRALIAN DIETARY GUIDELINES 2013 ---------------

Enjoy a wide variety of nutritious foods every day, including milk, yoghurt, cheese and/or their alternatives, mostly reduced fat.

Milk You may find a variety of fortified foods in the dairy case. Examples are milk, to which vitamins A and D may have been added, and soy milk to which calcium, vitamin D and vitamin B12 may have been added. In addition, you may find functional foods (e.g. margarine with added plant sterols). As food technology advances, such foods offer alternatives to traditional choices that assist people who want to reduce their fat and cholesterol intakes. Chapter 5 gives other examples. When shopping, choose low-fat milks , yoghurts and cheeses. Such selections help people meet their vitamin and mineral needs within their energy requirements.6 Dairy products are important sources of calcium but can provide too much sodium and fat if not selected with care.

2.3  Food labels

Be aware that not all soy milks have been fortified. Read labels carefully.

REVIEW IT

Food group plans, such as the Australian Guide to Healthy Eating, help people select the types and amounts of foods to provide adequacy, balance and variety in the diet. They make it easier to plan a diet that includes a balance of grains, vegetables, fruits, meats and dairy products. In making any food choice, remember to view the food in the context of your total diet. The combination of many different foods provides the abundance of nutrients that is so essential to a healthy diet.

Many people read food labels to assist with healthy choices. Food labels appear on virtually all packaged foods (see Figure 2.5). A few foods need not carry nutrition labels: fresh fruit, vegetables, nuts, lentils, beans, fresh meat and fish; those contributing few nutrients, such as plain coffee, tea and spices; those produced by small businesses; and those prepared and sold in the same establishment. Producers of some of these items, however, use labels voluntarily.

53

Reminder: Functional foods contain physiologically active compounds that provide health benefits beyond basic nutrition. Milk descriptions: • fat-free milk may also be called non-fat, skim, zero-fat or no-fat. • low-fat milk contains approximately 1.5% fat (1.5 g/100 mL). • reduced-fat milk refers to milk containing approximately 2% fat (2 g/100 mL).

All packaged foods must list all ingredients on the label in descending order of predominance by ingoing weight. The exception is water. Knowing that the first ingredient predominates by ingoing weight, people can glean much information. Compare these products, for example: • a beverage powder that contains ‘sugar, citric acid, natural flavours …’ versus a juice that contains ‘water, tomato concentrate, concentrated juices of carrots, celery …’ • a cereal that contains ‘puffed milled corn, sugar, corn syrup, molasses, salt …’ versus one that contains ‘100 per cent rolled oats’ • a canned fruit that contains ‘sugar, apples, water’ versus one that contains simply ‘apples, water’. In each of these comparisons, people can see that the second product is the more nutrient dense.

Shutterstock.com/Monkey Business Images

The ingredient list

People read food labels to learn about the nutrient contents of a food or to compare foods.

Understanding Nutrition

FIGURE 2.5   Example of a food label

© Food Standards Australia New Zealand.

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Chapter 2: Planning a healthy diet

Serving sizes Because labels present nutrient information per serving, they must identify the size of the serving. FSANZ has established that, along with serving size information, products must also list nutrition information for 100 grams (or 100 mL) of the food product. This facilitates the comparison of foods that are a different size or do not fall within the same food group. People can see at a glance which product has more or fewer kilojoules, grams of fat or calcium, for example (see Figure 2.5). Table 2.6 shows common household and metric measures.

TABLE 2.6   Household and metric measures 1 teaspoon (tsp) = 5 millilitres (mL) 1 tablespoon (tbs) = 20 mL 1 cup (c) = 250 mL

When examining the nutrition facts on a food label, people need to compare the serving size on the label with how much they actually eat and adjust their calculations accordingly. For example, if the serving size is two breakfast wheat biscuits and you only eat one, then you need to cut the nutrient and kilojoule values in half; similarly, if you eat four, then you need to double the values. Notice, too, that small bags or individually wrapped items, such as chips or chocolate bars, may contain more than a single serving. The number of servings per package is listed in the nutrition information panel, generally just above the serving size. Be aware that serving sizes on food labels are not always the same as those in Australian or New Zealand guidelines. For example, a serving of rice on a food label may be 1 cup, whereas in the Australian Guide to Healthy Eating it is ½ cup. This discrepancy, coupled with each person’s own perception of standard serving sizes, sometimes creates confusion for people trying to follow recommendations.

PUTTING COMMON SENSE TO THE TEST

The suggested serving size on food labels is often the same as the recommended serving in the Australian Guide to Healthy Eating. FALSE

Nutrition facts In addition to the serving size and the servings per container, FSANZ requires that the ingredients list on food packaging presents ingredient information as a percentage of the product (see Figure 2.5).

Nutrient claims Have you noticed phrases such as ‘contains fibre’ on a box of cereal or ‘reduced fat’ on a package of cheese? These and other nutrient claims may be used on labels as long as they meet FSANZ definitions, which include the conditions under which each term can be used. For example, a product claiming to be ‘low fat’ must contain no more than 1.5 grams of fat per 100 millilitres for drinks and other liquid foods and no more than 3 grams of fat per 100 grams for all other foods.

Health claims The FSANZ Food Standard (Standard 1.2.7) relating to nutrition, health claims and related claims provides people with more information for healthier food choices, and the food industry with greater incentives to develop healthier food products.7 Examples of nutrition content terms you may find on food labels are shown in Table 2.7.

PUTTING COMMON SENSE TO THE TEST

Food companies can put anything they like on their food labels. FALSE

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TABLE 2.7   Examples of nutrition content terms you may find on food labels TERM

EXPLANATION

Low fat or low in fat

The food must not contain more than 3 g of fat per 100 g of solid food (or 1.5 g of fat per 100 mL of liquid food)

Reduced fat or less fat

The food contains at least 25 per cent less fat than the same quantity of the reference food

Low cholesterol or low in cholesterol

The food must not contain more than 20 mg cholesterol per 100 g of solid food or 10 mg per 100 mL of liquid food and must meet the conditions for a nutrition content claim about low saturated fatty acids

Low sugar or low in sugar

The food must not contain more than 5 g of sugar per 100 g of solid food or 2.5 g of sugar per 100 mL of liquid food

Source of fibre or contains fibre

The food contains at least 2 g of dietary fibre per serving of food

Good source of fibre

The food must not contain less than 4 g of dietary fibre per serving of food

Reduced salt/sodium

The food must contain at least 25 per cent less sodium than the same quantity of reference food

Low in salt

Low in salt means the food contains less than 120 mg of sodium per 100 g or 100 mL

No artificial colourings or flavours

Negative claims are statements that claim the non-addition or absence of a substance in a food. Such claims, especially referring to food additives, are a quick and effective way of communicating to people. Negative claims are commonly made about no artificial colourings or flavourings, no flavour enhancers or preservatives, or no added sugar © Food Standards Australia New Zealand.

The health claims are categorised according to level of claim and must be substantiated by scientific evidence: • Nutrition content claims are statements regarding the amount of a nutrient, energy or a biologically active substance in the food. Manufacturers must have proof that the nutrient, substance or property that is the subject of the claim is present at levels referred to in the claim. • General level health claims can refer to the presence of a nutrient or substance in a food and to its effect on a health function. A general level health claim cannot refer to a serious disease or condition or to an indicator of a serious disease (e.g. blood cholesterol). Manufacturers must use either the FSANZ Model List of pre-approved statements, provide suitable scientific texts or dietary guidelines to support the claim, or hold scientific evidence to substantiate such claims and produce this evidence, on request, for enforcement agencies. • High-level health claims are those claims that make reference to a serious disease or biomarker and will need to be pre-approved by FSANZ, with approved claims being listed in the standard. Examples of claims that may be used can be seen in Table 2.8.

Chapter 2: Planning a healthy diet

TABLE 2.8   Examples of the levels of health claims that may be made on food packaging DESCRIPTION OF CLAIM Nutrition content claims Are claims about the content of certain nutrients or substances in a food. These claims will need to meet certain criteria set out in the Standard

EXAMPLE This food is high in calcium.

General level health claims Refer to a nutrient or substance in a food and its effect on a health function. They must not refer to a serious disease or to a biomarker of a serious disease … maintenance of good health

Helps keep you regular as part of a high fibre diet

… a component and its function in the body

Calcium is good for strong bones and teeth

… specific benefits for performance and wellbeing in relation to foods

Gives you energy

… how a diet, food or component can modify a function beyond its role in normal growth and development

Exercise and a diet high in calcium helps build stronger bones

… potential for a food or component to assist in reducing the risk of or helping to control a nonserious disease or condition

Yoghurt high in X and Y as part of a healthy diet may reduce your risk of stomach upsets

High level health claims High level health claims must be based on a food–health relationship preapproved by FSANZ. All health claims are required to be supported by scientific evidence to the same degree of certainty, whether they are pre-approved by FSANZ or self-substantiated by food businesses. Food–health relationships derived from health claims approved in the European Union, Canada and the US have been considered for inclusion in the Standard Claim refers to the potential for a food or component to assist in controlling a serious disease or condition by either reducing risk factors or improving health

This food is high in calcium. Diets high in calcium may increase bone mineral density

Claim refers to the potential for a food or component to assist in reducing the risk of a serious disease or condition

This food is low in sodium. Diets low in sodium may reduce risk of elevated blood pressure © Food Standards Australia New Zealand.

This chapter provides the links to go from dietary guidelines to buying groceries and offers helpful tips for selecting nutritious foods. For additional information on foods, including organic foods, irradiated foods, genetically modified foods and more, turn to Chapter 19.

REVIEW IT

Food labels provide people with information they need to select foods that will help them meet their nutrition and health goals. When labels contain relevant information presented in a standardised, easy-to-read format, people are well prepared to plan and create healthful diets.

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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 The concept of nutrient density means eating more kilojoules to get more nutrients. FALSE

Sometimes we do eat more kilojoules to obtain more nutrients, but the concept of nutrient density is where we obtain more nutrients (e.g. iron) but eat less kilojoules (e.g. 300 instead of 450).

4 The suggested serving size on food labels is often the

same as the recommended serving in the Australian Guide to Healthy Eating FALSE



2 Dietary guidelines prescribe a set diet. FALSE

Dietary guidelines provide a number of guidelines for each food group depending on life-stage. The guidelines recognise that not everybody has exactly the same needs and so dietary intake will vary from person to person.

3 Frozen and canned vegetables are not a suitable alternative to fresh varieties. FALSE

The suggested serving size is determined by food manufacturers and is more often different to a serving size as indicated by the Australian Guide to Healthy Eating. This is why food labels must include nutrition information per 100 g or mL of the product.

5 Food companies can put anything they like on their food labels. FALSE

It is commonly recognised that ‘fresh is best’ but frozen or canned vegetables without added salt or fats can be equally as nutritious as their fresh counterparts.

Although many food companies try to make their products stand out from others, what is allowed on food labels is tightly regulated by FSANZ. This includes things such as health claims or benefits of the food product.

CRITICAL THINKING QUESTION 1  The dietary guidelines of Australia and New Zealand sometimes come under fire for being too restrictive, too confusing or unobtainable. Nutrition scientists

apply a critical eye to these guidelines. After researching this topic, what do you think?

NUTRITION PORTFOLIO Each chapter in this book ends with simple ‘Nutrition portfolio’ activities that invite you to review key messages and consider whether your personal choices are meeting the dietary goals introduced in the text. By keeping a journal of these ‘Nutrition portfolio’ assignments, you can examine how your knowledge and behaviours change as you progress in your study of nutrition. The secret to making healthy food choices is learning to incorporate the Australian Dietary Guidelines and the Australian Guide to Healthy Eating into your decisionmaking process. • Compare the foods you typically eat daily with the Australian Guide to Healthy Eating recommendations

•

•

•

for your energy needs (see Table 2.3), making note of which food groups are usually over- or underrepresented in your diet. Describe your choices within each food group from day to day. Are there any realistic suggestions for enhancing the variety in your diet? Write your future self a letter describing the dietary changes you can make now to improve your chances of enjoying good health later in life. These do not have to be major changes. Try to implement the changes you suggested in your letter and develop good eating habits now.

STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1 What is the diet-planning principle that provides all the essential nutrients in sufficient amounts to support health? a Balance b Variety c Adequacy d Moderation

2

A person who eats a food that provides 250 milligrams of calcium and 600 kilojoules instead of a food that provides 200 milligrams of calcium and 750 kilojoules is using the principle of nutrient: a control b density c adequacy d moderation

Chapter 2: Planning a healthy diet

3

4

5

Which of the following is consistent with the Australian Dietary Guidelines? a Choose a diet restricted in fat and cholesterol. b Eat plenty of vegetables, legumes and fruits. c Balance the food you eat with physical activity. d Eat an abundance of foods to ensure nutrient adequacy. According to the Australian Guide to Healthy Eating, what are added fats counted as? a Meats and grains b Nutrient-dense foods c Discretionary kilojoules d Discretionary foods Foods within a given food group of the Australian Guide to Healthy Eating are similar in their contents of: a energy b proteins and fibre

6

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c vitamins and minerals d carbohydrates and fats In what order are the ingredients on food labels listed? a Alphabetical order b Ascending order of predominance by weight c Descending order of predominance by weight d Manufacturer’s order of preference What is ‘low in fat’ an example of? a Health claim b Nutrition fact c Nutrient content claim d Nutrition advertising

REVIEW QUESTIONS 1

Name the diet-planning principles and briefly describe how each principle helps in diet planning. (Section 2.1)

4

2

What recommendation is modified in the Australian Dietary Guidelines for children under the age of two years? Why do you think this is the case? (Section 2.1)

Review the Australian Dietary Guidelines. What types of food selections could you make to achieve those recommendations? (Section 2.1)

5

3

What are the differences and similarities between the Australian Guide to Healthy Eating plate and the Nutrition Australia Healthy Eating Pyramid? Do you think any differences might be confusing to the

6

What do you think is the most helpful information you can expect to find on a food label? When comparing nutrition information panels, how can this information help you choose between two products? (Section 2.3) What is a nutrient claim? How does this differ from a health claim? (Section 2.3)

general public? Outline your reasons why or why not. (Section 2.2)

NUTRITION CALCULATIONS These problems will give you practice in doing simple nutrition-related calculations. Although the situations are hypothetical, the numbers are real, and calculating the answers (see the Answers section at the back of this book) provides a valuable nutrition lesson. Be sure to show your calculations for each problem. 1 Read a food label. Look at the label in Figure 2.5 and answer the following questions: a What is the size of a serving of the product? b How many kilojoules are in a serving? c How much fat is in a serving?

d e f g h i

How many kilojoules does this amount of fat provide? What percentage of the kilojoules in this product comes from fat? What does this tell you? Does this product meet the criteria for a low-fat product (refer to Table 2.7)? What is the predominant ingredient in the product? Have any nutrients been added to this product (is it fortified)?

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New

Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search for ‘food labels’ at the FSANZ website: http:// www.foodstandards.gov.au

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Understanding Nutrition

Learn more about the Australian Dietary Guidelines at: http://www.eatforhealth.gov.au Find New Zealand information on nutrition guidelines and food labels at http://www.foodstandards.govt.nz Learn more about the Healthy Eating Pyramid: http://www.nutritionaustralia.org Visit the Traditional Diet Pyramids for various ethnic groups at Oldways Preservation and Exchange Trust: http://www.oldwayspt.org Visit the United States Department of Agriculture website and view ‘My Plate’: https://www.myplate.gov and compare it to the Australian version

•

•

•

Search ‘food labels’ at the International Food Information Council Foundation: https://www. foodinsight.org Read about the Health Star Rating, which is now on many New Zealand and Australian packaged foods: http://healthstarrating.gov.au/internet/ healthstarrating/publishing.nsf/content/home Get healthy eating tips from the ‘Go for 2&5’ program: http://www.gofor2and5.com.au

Chapter 2: Planning a healthy diet

2.4 VEGETARIAN DIETS

HIGHLIGHT

2

phytochemicals and little fat. These diets reflect current dietary recommendations aimed at promoting health and reducing obesity. Each of these foods – whole grains, vegetables, legumes, nuts and fruits – independently reduces the risk for several chronic diseases.1 This highlight examines the health benefits and potential problems of vegetarian diets and shows how to plan a well-balanced vegetarian diet.

Shutterstock.com/AS Food studio

The waiter presents this evening’s specials: a fresh spinach salad topped with mandarin, raisins and sunflower seeds, served with a bowl of pasta smothered in a mushroom and tomato sauce and topped with grated parmesan cheese. Then this one: a salad made of chopped parsley, shallots, celery and tomatoes mixed with couscous and dressed with olive oil and lemon juice, served with a spinach and feta cheese pie. Do these meals sound good to you? Or is something missing … some lean chicken breast or a steak, perhaps? Would vegetarian fare be acceptable to you some of the time? Most of the time? Ever? Perhaps it is helpful to recognise that dietary choices fall along a continuum – from one end, where people eat no meat or foods of animal origin, to the other end, where they eat generous quantities daily. The place of meat in the diet has been the subject of much research and controversy, as this highlight will reveal. One of the reasons for this highlight, in fact, is to identify the range of meat intakes most compatible with health. The health benefits of a primarily vegetarian diet seem to have encouraged many people to eat more vegetarian meals. People who choose to exclude meat and other animalderived foods from their diets today do so for many of the same reasons the Greek philosopher Pythagoras cited in the sixth century BCE – physical health, ecological responsibility and philosophical concerns. They might also cite world hunger issues, economic reasons, ethical concerns or religious beliefs as motivating factors. Whatever their reasons – and even if they do not have a particular reason – people who exclude meat are better prepared to plan well-balanced meals if they understand the nutrition and health implications of vegetarian diets. Vegetarians are generally categorised not by their motivations but by the foods they choose to exclude. Some people exclude red meat only, some also exclude chicken or fish, others also exclude eggs, and still others exclude milk and milk products as well. In fact, finding agreement on the definition of the term vegetarian is challenging. However, in the context of vegetarian diets, the foods excluded are not nearly as important as the foods included in the diet. Well-balanced vegetarian diets that include a variety of whole grains, vegetables, legumes, nuts and fruits offer abundant complex carbohydrates and fibre, an assortment of vitamins and minerals, a mixture of

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A vegetarian meal may contain vegetables, seeds and tofu.

Health benefits of vegetarian diets There has been much research on the health implications of vegetarian diets. Researchers must account for any lifestyle differences between vegetarian and non-vegetarian populations before they can determine which aspects of health correlate just with diet. Even then, correlations merely reveal what health factors go with the vegetarian diet, not what health effects may be caused by the diet. Despite these limitations, research findings suggest that well-planned vegetarian diets offer sound nutrition and health benefits to adults.2 Dietary patterns that include very little, if any, meat may even increase life expectancy.3

Weight control In general, vegetarians maintain a lower and healthier body weight than non-vegetarians.4 Vegetarians’ lower body weights correlate with their high intakes of fibre and low intakes of fat. Because obesity impairs health

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in a number of ways, this gives vegetarians a health advantage.

Blood pressure Vegetarians tend to have lower blood pressure and lower rates of hypertension than non-vegetarians. Appropriate body weight helps to maintain a healthy blood pressure, as does a diet low in total fat and saturated fat and high in fibre, fruits, vegetables and soy protein.5 Lifestyle factors also influence blood pressure: smoking and alcohol intake raise blood pressure, and physical activity lowers it.

Heart disease The incidence of ischaemic heart disease deaths is as much as 24 per cent lower for vegetarians than for meat eaters.6 The dietary factor most directly related to heart disease is saturated animal fat and, generally, vegetarian diets are lower in total fat, saturated fat and cholesterol than typical meat-based diets. The fats common in plant-based diets – the monounsaturated fats of olives, seeds and nuts and the polyunsaturated fats of vegetable oils – are associated with a decreased risk of heart disease.7 Furthermore, vegetarian diets are generally higher in dietary fibre, antioxidant vitamins and phytochemicals – all factors that help control blood lipids and protect against heart disease. Many vegetarians include soy products, such as tofu, in their diets. Soy products may help to protect against heart disease because they contain polyunsaturated fats, fibre, vitamins and minerals, and little saturated fat. Even when intakes of energy, protein, carbohydrate, total fat, saturated fat, unsaturated fat, alcohol and fibre are the same, people eating meals based on tofu have lower blood cholesterol and triglyceride levels than those eating meat. Some research suggests that soy protein and phytochemicals may be responsible for some of these health benefits (as Highlight 13 explains in greater detail).8

Cancer Vegetarians have a significantly lower rate of cancer than the general population. Their low cancer rates may be due to their high intakes of fruits and vegetables. In fact, the ratio of vegetables to meat may be the most relevant dietary factor responsible for cancer prevention.9 Some scientific findings indicate that vegetarian diets are associated not only with lower cancer mortality in general, but also with lower incidence of cancer at specific sites as well – most notably, colon cancer.10 People with colon cancer seem to eat more meat, more saturated fat and fewer vegetables than do people without colon cancer. High-protein, high-fat, low-fibre diets create an environment in the colon that promotes the development of cancer in some people. Additionally, high-meat diets have been associated with stomach cancer.11

Other diseases In addition to obesity, hypertension, heart disease and cancer, vegetarian diets may help prevent diabetes, osteoporosis, diverticular disease, gall stones and rheumatoid arthritis.12 These health benefits of a vegetarian diet depend on wise diet planning.

Vegetarian diet planning Vegetarians have the same meal-planning task as any other person – using a variety of foods to deliver all the needed nutrients within an energy allowance that maintains a healthy body weight (as discussed earlier in Chapter 2). Vegetarians who include milk products and eggs can meet recommendations for most nutrients as easily as nonvegetarians. Such diets can provide enough energy, protein and other nutrients to support the health of adults. Vegetarians who exclude milk products and eggs can select legumes, nuts and seeds, and products made from them, such as peanut butter, tempeh and tofu, to replace products from the meat group. Those who do not use milk can use a dairy alternative, such as soy or nut milks, if they are fortified with calcium (and sometimes vitamin B12). When selecting from vegetable and fruit groups, vegetarians should emphasise particularly good sources of calcium and iron, respectively. Green leafy vegetables, for example, provide almost five times as much calcium per serving as other vegetables. Similarly, dried fruits deserve special notice in the fruit group because they deliver six times as much iron as other fruits. Fortified soy products may be used to replace milk products for those who do not use milk, cheese or yoghurt. Meat products may be replaced by legumes, soy products, nuts and seeds. To ensure adequate intakes of vitamin B12, vitamin D and calcium, vegetarians need to select fortified foods or take supplements regularly. Most vegetarians easily obtain large quantities of the nutrients that are abundant in plant foods: thiamin, folate and vitamins B6, C, A and E. Good planning of vegetarian diets using the Australian Guide to Healthy Eating and Nutrition Australia’s Healthy Eating Pyramid (see Figure 2.2) can help to ensure adequate intake of the main nutrients vegetarian diets might otherwise lack: protein, iron, zinc, calcium, vitamin B12, vitamin D and omega-3 fatty acids.

Protein The protein Recommended Dietary Intake for vegetarians is the same as for non-vegetarians, although some have suggested that it should be higher because of the lower digestibility of plant proteins.13 Lacto-ovo-vegetarians, who use animal-derived foods, such as milk and eggs, receive high-quality proteins and are likely to meet their protein needs. Even those who adopt only plant-based

Chapter 2: Planning a healthy diet

diets are likely to meet protein needs, provided that their energy intakes are adequate and the protein sources varied. The proteins of whole grains, legumes, seeds, nuts and vegetables can provide adequate amounts of all the amino acids. An advantage of many vegetarian sources of protein is that they are generally lower in saturated fat than meats and are often higher in fibre and richer in some vitamins and minerals. Vegetarians sometimes use meat replacements made of textured vegetable protein (soy protein). These foods are formulated to look and taste like meat, fish or poultry. Many of these products are fortified to provide the vitamins and minerals found in animal sources of protein. A wise vegetarian learns to use a variety of whole, unrefined foods often, and commercially prepared foods less frequently. Vegetarians may also use soy products, such as tofu, to bolster protein intake.

Iron Getting enough iron can be a problem even for meat eaters, and those who eat no meat must pay special attention to their iron intake. The iron in plant foods, such as legumes, dark green leafy vegetables, iron-fortified cereals and wholegrain breads and cereals, is called nonhaem iron and is not absorbed as well as haem iron found in animal products.14 Fortunately, the body adapts to a vegetarian diet by absorbing iron more efficiently, but vegetarians need to be thoughtful with their diet planning. Iron absorption is enhanced by vitamin C, and vegetarians typically eat many vitamin C-rich fruits and vegetables. Consequently, vegetarians tend to suffer no more iron deficiency than other people do.15

Zinc Zinc is similar to iron in that meat is its richest food source, and zinc from plant sources is not absorbed well.16 In addition, soy, which is commonly used as a meat alternative in vegetarian meals, interferes with zinc absorption. Nevertheless, most vegetarian adults are not zinc deficient. Perhaps the best advice to vegetarians regarding zinc is to eat a variety of nutrient-dense foods; include whole grains, nuts and legumes, such as blackeyed peas, pinto beans and kidney beans; and maintain an adequate energy intake. For those who include seafood in their diets, oysters, crabmeat and prawns are rich in zinc.

Calcium

The calcium intakes of lacto-vegetarians are similar to those of the general population, but people who use no milk products risk deficiency. Careful planners select calcium-rich foods, such as calcium-fortified juices, soy beverages and breakfast cereals, in ample quantities

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regularly. This advice is especially important for children and adolescents. Other good calcium sources include figs, some legumes, some green vegetables such as broccoli and spinach, some nuts, such as almonds, certain seeds, such as sesame seeds, and calcium-set tofu (calcium salts are often added during processing to coagulate the tofu). The choices should be varied because calcium absorption from some plant foods may be limited (as Chapter 12 explains).

Vitamin B12

The requirement for vitamin B12 is small, but this vitamin is found only in animal-derived foods. Consequently, vegetarians, in general, and particularly vegans who eat no foods of animal origin, may not get enough vitamin B12 in their diets. Fermented soy products, such as tempeh, may contain some vitamin B12 from the bacteria, but unfortunately, much of this may be an inactive form. Seaweeds, such as nori and chlorella, supply some vitamin B12 but not much, and excessive intakes of these foods can lead to iodine toxicity. To defend against vitamin B12 deficiency, vegans must rely on vitamin B12–fortified sources (e.g. soy beverages) or supplements. Without vitamin B12, the nerves suffer damage, leading to such health consequences as loss of vision.

Vitamin D People who do not use vitamin D–fortified foods and do not receive enough exposure to sunlight to synthesise adequate vitamin D may need supplements to defend against bone loss. This is particularly important for infants, children and older adults.

Omega-3 fatty acids Both Chapter 5 and Highlight 5 describe the health benefits of unsaturated fats, most notably the omega-3 fatty acids commonly found in fatty fish. To obtain sufficient amounts of omega-3 fatty acids, vegetarians (who do not eat fish products either) need to consume flaxseed, walnuts, soybeans and products derived from these.

Healthy food choices In general, adults who eat vegetarian diets have lower risks of mortality and several chronic diseases, including obesity, high blood pressure, heart disease and cancer. But there is nothing mysterious or magical about the vegetarian diet. Vegetarianism is not a religion like Buddhism or Hinduism but merely an eating plan that selects plant foods to deliver needed nutrients. The quality of the diet depends not on whether it includes meat but on whether the food choices are nutritionally sound. A diet that includes ample fruits,

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vegetables, whole grains, legumes, nuts and seeds is higher in fibre, antioxidant vitamins and phytochemicals, and lower in saturated fats than meat-based diets. Variety is key to nutritional adequacy in a vegetarian diet. Restrictive plans, such as macrobiotic diets, that limit selections to a few grains and vegetables, cannot possibly deliver a full array of nutrients. If not properly balanced, any diet – vegetarian or otherwise – can lack nutrients. Poorly planned vegetarian diets typically lack iron, zinc, calcium, vitamin B12 and vitamin D; without planning, the meat eater’s diet may lack vitamin A, vitamin C, folate and fibre, among others.

Quite simply, the negative health aspects of any diet, including vegetarian diets, reflect poor diet planning. Careful attention to energy intake and specific problem nutrients can ensure adequacy. Keep in mind, too, that diet is only one factor influencing health. Whatever a diet consists of, its context is also important: not smoking, alcohol consumption in moderation, regular physical activity, adequate rest and medical attention when needed all contribute to a healthy life. Establishing these healthy habits early in life seems to be the most important step one can take to reduce the risks of later diseases (see Highlight 16).

HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1

Are vegetarian diets healthier than non-vegetarian diets? Outline why you believe they are/are not.

2

Your interest in nutrition has been piqued by the concept of a vegetarian diet, and you recognise that a well-planned vegetarian diet involves more than simply replacing a chicken sandwich with a large green

salad. Design and follow a vegetarian meal plan for three days. Try to include one vegan day. Outline the social, personal, and nutritional challenges you faced. Do any of these challenges inhibit or encourage you to integrate vegetarian meals into your current meal plan?

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Data­base provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx

• • •

Search for ‘vegetarian’ at the US Food and Drug Administration’s site: http://www.fda.gov Visit the site of the Australian Vegetarian and Vegan Society: http://www.vegsa.org.au Review another vegetarian diet pyramid developed by Oldways Preservation & Exchange Trust: http://www. oldwayspt.org

REFERENCES CHAPTER 1

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A. Drewnowski and co-authors, A proposed nutrient density score that includes food groups and nutrients to better align with dietary guidance, Nutrition Reviews 77 (2019): 404–416. Position of the Academy of Nutrition and Dietetics: Total diet approach to healthy eating, Journal of the Academy of Nutrition and Dietetics 113 (2013): 307–317. National Health and Medical Research Council, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2013), available at https://www.eatforhealth.gov.au Ministry of Health, Eating and Activity Guidelines for New Zealand Adults (2020) Wellington: Ministry of Health.

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Department of Health and Ageing, Australian Guide to Healthy Eating, Canberra: Commonwealth of Australia (2013), available at https:// www.eatforhealth.gov.au E. Trichia and co-authors, Associations of types of dairy consumption with adiposity: cross-sectional findings from over 12  000 adults in the Fenland Study, UK, The British Journal of Nutrition 122 (2019): 928–935. Food Standards Australia New Zealand, Standard 1.2.7 Nutrition, health & related claims, FSANZ, 2015, available at http://www. foodstandards.gov.au/publications/Pages/gettingyourclaimsright.aspx

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HIGHLIGHT 1

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4 5

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M. Dinu and co-authors, Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies, Critical Reviews in Food Science and Nutrition 57 (2017): 3640–3649. Position of the Academy of Nutrition and Dietetics, Vegetarian diets, Journal of the Academy of Nutrition and Dietetics, 116 (2016): 1970–1980; US Department of Health and Human Services and US Department of Agriculture, 2015–2020 Dietary Guidelines for Americans, 8th ed. (2015), http://health.gov/dietaryguidelines/2015/ guidelines V. Zhong and co-authors, Associations of processed meat, unprocessed red meat, poultry, or fish intake with incident cardiovascular disease and all-cause mortality, JAMA Internal Medicine 180 (2020): 503–512. P. N. Appleby and T. J. Key, The long-term health of vegetarians and vegans, Proceedings of the Nutrition Society 28 (2016): 1–7. J. Gibbs and co-authors, The effect of plant-based dietary patterns on blood pressure: A systematic review and meta-analysis of controlled intervention trials, Journal of Hypertension 39 (2021): 23–37. B. Jakše and co-authors, Dietary intakes and cardiovascular health of healthy adults in short-, medium-, and long-term whole-food plantbased lifestyle program, Nutrients 12 (2019): 5. G. Fraser and co-authors, Lower rates of cancer and all-cause mortality in an Adventist cohort compared with a US Census population, Cancer 126 (2020): 1102–1111.

R. Katagiri and co-authors, Association of soy and fermented soy product intake with total and cause specific mortality: prospective cohort study, British Medical Journal 34 (2020). doi: 10.1136/bmj.m34 9 G. Fraser and co-authors, Lower rates of cancer and all-cause mortality in an Adventist cohort compared with a US Census population. 10 Ibid. 11 C. Mattiuzzi and G. Lippi, Epidemiologic burden of red and processed meat intake on colorectal cancer mortality, Nutrition and Cancer 73 (2021): 562–567. 12 N. S. Rizzo and co-authors, Nutrient profiles of vegetarian and nonvegetarian dietary patterns, Journal of the Academy of Nutrition and Dietetics 113 (2013): 1610–1619. 13 F. Mariotti and C.D. Gardner, Dietary protein and amino acids in vegetarian diets – a review, Nutrients 11 (2019): 2661. 14 I. Young and co-authors, Association between haem and non-haem iron intake and serum ferritin in healthy young women, Nutrients 10 (2018): 81. 15 C. T. McEvoy, N. Temple, and J. V. Woodside, Vegetarian diets, low meat diets and health: A review, Public Health Nutrition 15 (2012): 2287–2294. 16 M. Maares and H. Haase, A guide to human zinc absorption: General overview and recent advances of in vitro intestinal models, Nutrients 12 (2020): 762. 8

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DIGESTION, ABSORPTION AND TRANSPORT Nutrition in your life

Have you ever wondered what happens to the food you eat after you swallow it? Or how your body extracts nutrients from food? Have you ever marvelled at how it all just seems to happen? Follow foods as they travel through the digestive system. Learn how a healthy digestive system transforms whatever food you give it – whether T-bone steak and potatoes or tofu and brussels sprouts – into the nutrients that will nourish the cells of your body. In the ‘Nutrition portfolio’ at the end of the chapter, you can determine whether your current eating habits are supporting a healthy digestive system. PUTTING COMMON SENSE TO THE TEST Circle your answer

T F Gastric juice has a pH similar to that of water and helps support bacterial growth in the

stomach.

T F The process of food digestion begins in the mouth and proceeds all the way into the large

intestine.

T F Veins and lymphatic vessels leaving the digestive tract carry nutrients to the body. T F The gastrointestinal tract is sterile throughout. T F The functions of the digestive tract are an example of the process of homeostasis.

LEARNING OBJECTIVES 3.1 Explain how foods move through the digestive system, describing the actions of the organs, muscles and digestive secretions along the way. 3.2 Describe the anatomical details of the intestinal cells that facilitate nutrient absorption. 3.3 Explain how nutrients travel in the circulatory systems from the

gastrointestinal tract into the body and identify which nutrients enter the blood directly and which must first enter the lymph. 3.4 Describe how bacteria, hormones and nerves influence the health and activities of the gastrointestinal tract. 3.5 Outline strategies to prevent or alleviate common gastrointestinal problems. Radish is highly rich in minerals like phosphorus and zinc that are beneficial for providing better skin texture

Chapter 3: Digestion, absorption and transport

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Each cell in the body needs a continuous supply of many specific nutrients to maintain itself and carry out its work. These nutrients derive from the foods consumed, but before the body’s cells can use the nutrients, foods must be broken down mechanically and chemically. This chapter follows the journey that breaks down foods into the nutrients featured in the later chapters. This introduction presents a general overview of the processes common to all nutrients; later chapters discuss the specifics of digesting and absorbing individual nutrients.

3.1 Digestion

your part. Consider these challenges: 1  Human beings breathe, eat and drink through their mouths. Air taken in through the mouth must go to the lungs; food and liquid must go to the stomach. The throat must be arranged so that swallowing and breathing do not interfere with each other. 2  Below the lungs lies the diaphragm, a dome of muscle that separates the upper half of the major body cavity from the lower half. Food must pass through this wall to reach the stomach. 3  The contents within the digestive tract should be kept moving forward, slowly but steadily, at a pace that permits all reactions to reach completion. 4  To move through the system, food must be lubricated with fluids. Too much would form a liquid that would flow too rapidly; too little would form a paste too dry and compact to move at all. The amount of fluids must be regulated to keep the intestinal contents at the right consistency to move smoothly along. 5  When the digestive enzymes break food down, they need it in a finely divided form, suspended in enough liquid so that every particle is accessible. Once digestion is complete and the needed nutrients have been absorbed out of the gastrointestinal (GI) tract and into the body, the system must excrete the remaining residue. Excreting all the water along with the solid residue, however, would be both wasteful and messy. Some water must be withdrawn to leave a paste just solid enough to be smooth and easy to pass. 6  The enzymes of the digestive tract are designed to digest carbohydrate, fat and protein. The walls of the tract, composed of living cells, are also made of carbohydrate, fat and protein. These cells need protection against the action of the powerful digestive juices that they secrete. 7  Once the residual matter has reached the end of the GI tract, it must be excreted, but it would be inconvenient and embarrassing if this function occurred continuously. Provision must be made for periodic, voluntary evacuation. The following sections show how the body elegantly and efficiently handles these challenges. Each section follows the GI tract from one end to the other – first describing its anatomy, then its muscular actions and finally its secretions.

Anatomy of the digestive tract The gastrointestinal (GI) tract is a flexible muscular tube that extends from the mouth, through the oesophagus, stomach, small intestine, large intestine and rectum to the anus. Figure 3.1 traces the path followed by food from one end to the other. In a sense, the human body surrounds the GI tract. The inner space within the GI tract, called the lumen, is continuous from one end to the other. Only when a nutrient or other substance finally

The process of digestion transforms all kinds of foods into nutrient.

Shutterstock.com/Hurst Photo

Digestion is the body’s ingenious way of breaking down foods into nutrients in preparation for absorption. In the process, it overcomes many challenges without any conscious effort on

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FIGURE 3.1   The gastrointestinal tract GI anatomy terms appear in boldface type and are defined in the Glossary. Appendix Stores lymph cells

INGESTION Mouth Chews and mixes food with saliva

Small intestine Secretes enzymes that digest all energy-yielding nutrients to smaller nutrient particles; cells of wall absorb nutrients into blood and lymph

Salivary glands

Pharynx Directs food from mouth to oesophagus

Pharynx

Mouth

Epiglottis Upper oesophageal sphincter

Salivary glands Secrete saliva (contains starch-digesting enzymes) Epiglottis Protects airway during swallowing

Trachea (to lungs)

Oesophagus

Trachea Allows air to pass to and from lungs Oesophagus Passes food from the mouth to the stomach Oesophageal sphincters Allow passage from mouth to oesophagus and from oesophagus to stomach; prevent backflow from stomach to oesophagus and from oesophagus to mouth

Stomach Adds acid, enzymes, and fluid; churns, mixes and grinds food to a liquid mass

Lower oesophageal sphincter Liver

Ileocaecal valve (sphincter) Allows passage from small to large intestine; prevents backflow from large intestine Pancreas Manufactures enzymes to digest all energy-yielding nutrients and releases bicarbonate to neutralise acid chyme that enters the small intestine Pancreatic duct Conducts pancreatic juice from the pancreas to the small intestine Stomach

Gall bladder

Pancreas

Pyloric sphincter

Pancreatic duct

Bile duct

Small intestine (duodenum, jejunum, ileum)

Ileocaecal valve Appendix

Pyloric sphincter Allows passage from stomach to small intestine; prevents backflow from small intestine

Large intestine (colon) Rectum

Liver Manufactures bile salts, detergent-like substances, to help digest fats

Anus

Gall bladder Stores bile until needed Bile duct Conducts bile from the gall bladder to the small intestine

Large intestine (colon) Reabsorbs water and minerals; passes waste (fibre, bacteria and unabsorbed nutrients) along with water to the rectum Rectum Stores waste prior to elimination Anus Holds rectum closed; opens to allow elimination ELIMINATION

penetrates the GI tract’s wall does it enter the body proper; many materials pass through the GI tract without being digested or absorbed.

Mouth

The process of chewing is called mastication.

The process of digestion begins in the mouth. As you chew, your teeth crush large pieces of food into smaller ones, and fluids from foods, beverages and salivary glands blend with these pieces to ease swallowing. Fluids also help dissolve the food so that you can taste it; only particles in solution can react with taste buds. When stimulated, the taste buds detect

Chapter 3: Digestion, absorption and transport

one, or a combination, of the five basic taste sensations: sweet, sour, bitter, salty and umami (a savoury flavour commonly associated with monosodium glutamate). In addition to these chemical triggers, aroma, texture and temperature also affect a food’s flavour. In addition to these chemical triggers, the aroma, appearance, texture and temperature of each food also influence a person’s taste perceptions. The tongue allows you not only to taste food, but also to move food around the mouth, facilitating chewing and swallowing. When you swallow a mouthful of food, it passes through the pharynx, a short tube that is shared by both the digestive system and the respiratory system. To bypass the entrance to your lungs, the epiglottis closes off your air passages so that you don’t choke when you swallow, thus resolving challenge 1. (Choking is discussed in Highlight 3.) After a mouthful of food has been swallowed, it is called a bolus.

Oesophagus

The oesophagus has a sphincter muscle at each end. During a swallow, the upper oesophageal sphincter opens. The bolus then slides down the oesophagus, which passes through a hole in the diaphragm (challenge 2) to the stomach. The lower oesophageal sphincter at the entrance to the stomach closes behind the bolus so that it proceeds forward and doesn’t slip back into the oesophagus (challenge 3).

Stomach The stomach retains the bolus for a while in its upper portion before transferring it to the lower portion. The stomach transfers the food to its lower portion, adds juices to it and grinds it to a semiliquid mass called chyme. Then, little by little, the stomach releases the chyme through the pyloric sphincter, which opens into the small intestine and then closes behind the chyme.

Small intestine

At the beginning of the small intestine, the chyme bypasses the opening from the common bile duct, which is dripping fluids (challenge 4) into the small intestine from two organs outside the GI tract – the gall bladder and the pancreas. The chyme travels on down the small intestine through its three segments – the duodenum, the jejunum and the ileum – over three metres of tubing coiled within the abdomen.

Large intestine (colon) Having travelled the length of the small intestine, the remaining contents arrive at another sphincter (challenge 3 again): the ileocaecal valve, located at the beginning of the large intestine (colon) in the lower right side of the abdomen. Upon entering the colon, the contents pass another opening. Any intestinal contents slipping into this opening would end up in the appendix, a blind sac about the size of your little finger. The contents bypass this opening, however, and travel along the large intestine up the right side of the abdomen, across the front to the left side, down to the lower left side and finally below the other folds of the intestines to the back of the body, above the rectum. (See Figure 3.2.) As the intestinal contents pass to the rectum, the colon withdraws water, leaving semisolid waste (challenge 5). The strong muscles of the rectum and anal canal hold back this waste until it is time to defecate. Then the rectal muscles relax (challenge 7), and the two sphincters of the anus open to allow passage of the waste.

The muscular action of digestion In the mouth, chewing, the addition of saliva and the action of the tongue transform food into a coarse mash that can be swallowed. After swallowing, you are generally unaware of all the activity that follows. As is the case with so much else that happens in the body, the muscles of

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FIGURE 3.2   The colon The colon begins with the ascending colon rising upwards towards the liver. It becomes the transverse colon as it turns and crosses the body towards the spleen. The descending colon turns downwards and becomes the sigmoid colon, which extends to the rectum. Along the way, the colon mixes the intestinal contents, absorbs water and salts, and forms stools.

Transverse colon

Ascending colon Opening from small intestine to large intestine

End of small intestine

Descending colon

Appendix Rectum Anus

The ability of the GI tract muscles to move is called motility.

Sigmoid colon

the digestive tract meet internal needs without any conscious effort on your part. They keep things moving at just the right pace – slow enough to get the job done and fast enough to make progress.

Segmentation and peristalsis Two layers of muscles in the GI tract (the inner circular and outer longitudinal muscles) coordinate to produce two different kinds of action – segmentation and peristalsis (challenge 3 again). In segmentation, the inner circular muscles contract and relax in a way that churns the chyme. Unlike peristalsis, which predominates in the oesophagus, segmentation contractions occur in the small and large intestines. While peristalsis involves one-way motion, segmentation contractions move chyme in both directions, which allows greater mixing with the secretions of the intestines. In peristalsis, the outer longitudinal muscles contract rhythmically in a way that moves chyme forward. These rhythmic contractions occur continuously at varying rates and intensities, depending on the section of the GI tract and whether food is present. Factors such as stress, drugs and illness may interfere with normal GI tract contractions.

Stomach action The stomach has the thickest walls and strongest muscles of all the GI tract organs. In addition to the circular and longitudinal muscles, it has a third layer of diagonal muscles that also alternately contract and relax (see Figure 3.3). These three sets of muscles work to force the chyme downwards, but the pyloric sphincter usually remains tightly closed, preventing the chyme from passing into the duodenum of the small intestine. As a result, the chyme is churned and forced down; it hits the pyloric sphincter and remains in the stomach. Meanwhile, the stomach wall releases gastric juices. When the chyme is completely liquefied, the pyloric sphincter opens briefly, about three times a minute, to

Chapter 3: Digestion, absorption and transport

allow small portions of chyme to pass through. At this point, the chyme no longer resembles food at all.

FIGURE 3.3   Stomach muscles Longitudinal

Sphincter contractions Sphincter muscles periodically open and close, allowing the contents of the GI tract to move along at a controlled pace (challenge 3 again). At the top of the oesophagus, the upper oesophageal sphincter opens in response to swallowing. At the Circular bottom of the oesophagus, the lower oesophageal sphincter Diagonal (sometimes called the cardiac sphincter because of its proximity to the heart) prevents reflux of the stomach contents. At the bottom of the stomach, the pyloric sphincter, which stays closed most of the time, holds the chyme in the stomach long enough for it to be thoroughly mixed with gastric juice and liquefied. The pyloric sphincter also prevents the intestinal contents from backing up into the stomach. At the end of the small intestine, the ileocaecal valve performs a similar function, allowing the contents of the small intestine to empty into the large intestine. Finally, the tightness of the rectal muscle is a kind of safety device; together with the two sphincters of the anus, it prevents elimination until the individual chooses to perform it voluntarily (challenge 7). Figure 3.4 illustrates how sphincter muscles contract and relax to close and open passageways.

The secretions of digestion The breakdown of food into nutrients requires secretions from five different organs: the salivary glands, stomach, pancreas, liver (via the gall bladder) and small intestine. These secretions enter the GI tract at various points along the way, bringing an abundance of water (challenge 3 again) and a variety of enzymes. Enzymes are formally introduced in Chapter 6, but for now we will simply define it as a protein that facilitates a chemical reaction – making a molecule, breaking a molecule apart, changing the arrangement of a molecule or exchanging parts of molecules. As a catalyst, the enzyme itself remains unchanged. The enzymes involved in digestion facilitate a chemical reaction known as hydrolysis – the addition of water (hydro) to break (lysis) a molecule into

FIGURE 3.4   An example of a sphincter muscle Circular muscle

Oesophagus

Longitudinal muscle Oesophagus muscles relax, opening the passageway

Stomach

Diaphragm muscles relax, opening the passageway

Oesophagus muscles contract, squeezing on the inside Diaphragm muscles contract, squeezing on the outside

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smaller pieces. The Glossary includes some of the common digestive enzymes and related terms. When learning about enzymes, it helps to know that words ending in -ase denote an enzyme. Enzymes are often identified by the organ they come from and the compounds they work on. Gastric lipase, for example, is a stomach enzyme that acts on lipids, whereas pancreatic lipase comes from the pancreas (and also works on lipids). Because of all these secretions, the three energy-yielding nutrients – carbohydrate, fat and protein – are digested in the small intestine. (Table 3.1 provides a list of digestive secretions and their actions.)

TABLE 3.1   Summary of digestive secretions and their major actions ORGAN OR GLAND

TARGET ORGAN

SECRETION

ACTION

Salivary glands

Mouth

Saliva

Fluid eases swallowing; salivary enzyme breaks down some carbohydrate*

Gastric glands

Stomach

Gastric juice

Fluid mixes with bolus; hydrochloric acid uncoils proteins; enzymes break down proteins; mucus protects stomach cells*

Pancreas

Small intestine

Pancreatic juice

Bicarbonate neutralises acidic gastric juices; pancreatic enzymes break down carbohydrates, fats and proteins

Liver

Gall bladder

Bile

Bile is stored until needed

Gall bladder

Small intestine

Bile

Bile emulsifies fat so that enzymes can have access to break it down

Intestinal glands

Small intestine

Intestinal juice

Intestinal enzymes break down carbohydrate, fat and protein fragments; mucus protects the intestinal wall

*Saliva and gastric juice also contain lipases, but most fat breakdown occurs in the small intestine.

FIGURE 3.5   The salivary glands

Saliva

The salivary glands, shown in Figure 3.5, squirt just enough saliva to moisten each mouthful of food so that it can pass easily down the oesophagus (challenge 4). Digestive glands and their secretions are defined in the Glossary. The saliva contains water, salts, mucus and enzymes that initiate the digestion of carbohydrates. Saliva also protects the teeth and the linings of the mouth, oesophagus and stomach from attack by substances that might harm them.

Gastric juice

Salivary glands

PUTTING COMMON SENSE TO THE TEST

Gastric juice has a pH similar to that of water and helps support bacterial growth in the stomach. FALSE

In the stomach, gastric glands secrete gastric juice, a mixture of water, enzymes and hydrochloric acid, which acts primarily in protein digestion. The acid is so strong that it causes the sensation of heartburn if it happens to reflux into the oesophagus. Highlight 3, at the end of this chapter, discusses heartburn, ulcers and other common digestive problems. The strong acidity of the stomach prevents bacterial growth and kills most bacteria that enter the body with food. It would destroy the cells of the stomach as well, but for their natural defences. To protect themselves from gastric juice, the cells of the stomach wall secrete mucus, a thick, slippery, white substance that coats the cells, protecting them from the acid, enzymes and disease-causing bacteria that might otherwise harm them (challenge 6). Figure 3.6 shows how the strength of acids is measured – in pH units. Note that the acidity of gastric juice registers below ‘2’ on the pH scale – stronger than vinegar. The stomach enzymes work most efficiently in the stomach’s strong acid, but the salivary enzymes, which are swallowed with food, do not work in acid this strong. Consequently, the salivary digestion of carbohydrate gradually ceases when the stomach acid penetrates each newly swallowed bolus of food. When they enter the stomach, salivary enzymes become just other proteins to be digested.

Chapter 3: Digestion, absorption and transport

Pancreatic juice and intestinal enzymes By the time food leaves the stomach, digestion of all three energy nutrients (carbohydrates, fats and proteins) has begun, and the action gains momentum in the small intestine. There the pancreas contributes digestive juices by way of ducts leading into the duodenum. The pancreatic juice contains enzymes that act on all three energy nutrients, and the cells of the intestinal wall also possess digestive enzymes on their surfaces. In addition to enzymes, the pancreatic juice contains sodium bicarbonate, which is basic or alkaline – the opposite of the stomach’s acid (review Figure 3.6). The pancreatic juice thus neutralises the acidic chyme arriving in the small intestine from the stomach. From this point on, the chyme remains at a neutral or slightly alkaline pH. The enzymes of both the intestine and the pancreas work best in this environment.

Bile

Bile also flows into the duodenum. The liver continuously produces

FIGURE 3.6   The pH scale pH of common substances: Basic

14

Concentrated lye

13

Oven cleaner

12 11

Household ammonia

10 9

6

Baking soda Bile Pancreatic juice Blood Water Saliva Urine

5

Coffee

4

Orange juice

3

Vinegar

2

Lemon juice Gastric juice

8 pH neutral

7

bile, which is then concentrated and stored in the gall bladder. The gall bladder squirts the bile into the duodenum of the small intestine when fat arrives there. Bile is not an enzyme; it is an emulsifier that brings fats into suspension in water so that enzymes can break them down into their component parts.

The final stage By the time the contents of the GI tract reach the end of the small intestine, the three energy-yielding nutrients – carbohydrate, fat and protein – have been digested and are ready to be absorbed. Most vitamins and minerals Acidic are absorbed as they are, but some are altered slightly during digestion. The remaining fluids, a few dissolved salts and undigested materials, such as fibre, enter the large intestine (colon). Fibre carries with it some fat, cholesterol and a few minerals and it also retains water, accounting for the pasty consistency of stools. In the colon, intestinal bacteria ferment some types of dietary fibre, producing water, gas and small fragments of fat that provide energy for the cells of the colon. The colon itself retrieves all materials that the body can recycle – water and dissolved salts (see Figure 3.7). The waste that is finally excreted has little or nothing of value left in it. The body has extracted all that it can use from the food. Figure 3.7 summarises digestion by following a sandwich through the GI tract and into the body.

Within three or four hours of having eaten a dinner of meat and vegetables with salad, a drink and dessert, your body must find a way to absorb the molecules derived from carbohydrate, protein and fat digestion – and the vitamin and mineral molecules as well. Most absorption takes place in the small intestine, one of the most elegantly designed organ systems in the body. Within its three-metre length, which provides a surface area equivalent to a tennis court, the

1 0

Battery acid

The lower the pH, the higher the H+ ion concentration and the stronger the acid. A pH above 7 is alkaline, or base (a solution in which OH− ions predominate).

REVIEW IT

As Figure 3.1 shows, food enters the mouth and travels through the upper oesophageal sphincter, down the oesophagus and through the lower oesophageal sphincter to the stomach, then through the pyloric sphincter to the small intestine, on through the ileocaecal valve to the large intestine, past the appendix to the rectum, ending at the anus. The wave-like contractions of peristalsis and the periodic squeezing of segmentation keep things moving at a reasonable pace. Along the way, secretions from the salivary glands, stomach, pancreas, liver (via the gall bladder), and small intestine deliver fluids and digestive enzymes.

3.2 Absorption

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PUTTING COMMON SENSE TO THE TEST

The process of food digestion begins in the mouth and proceeds all the way into the large intestine. TRUE

Understanding Nutrition

Fat

tein Pro

Carbohydrate digestion begins as the salivary enzyme starts to break down the starch from bread and peanut butter.

Fib re

MOUTH: CHEWING AND SWALLOWING, WITH LITTLE DIGESTION

boh ydr ate

FIGURE 3.7   The digestive fate of a sandwich

Car

74

Fibre covering on the sesame seeds is crushed by the teeth, which exposes the nutrients inside the seeds to the upcoming digestive enzymes.

STOMACH: COLLECTING AND CHURNING, WITH SOME DIGESTION Carbohydrate digestion continues until the mashed sandwich has been mixed with the gastric juices; the stomach acid of the gastric juices inactivates the salivary enzyme and carbohydrate digestion ceases. Proteins from the bread, seeds and peanut butter begin to uncoil when they mix with the gastric acid, making them available to the gastric protease enzymes that begin to digest proteins. Fat from the peanut butter forms a separate layer on top of the watery mixture.

SMALL INTESTINE: DIGESTING AND ABSORBING Sugars from the banana require so little digestion that they begin to traverse the intestinal cells immediately on contact. Starch digestion picks up when the pancreas sends pancreatic enzymes to the small intestine via the pancreatic duct. Enzymes on the surfaces of the small intestinal cells into small fragments that can be absorbed through the intestinal cell walls and into the hepatic portal vein. Fat from the peanut butter and seeds is emulsified with the watery digestive fluids by bile. Now the pancreatic and intestinal lipases can begin to break down the fat to smaller fragments that can be absorbed through the cells of the small intestinal wall and into the lymph. Protein digestion depends on the pancreatic and intestinal proteases. Small fragments of protein are liberated and absorbed through the cells of the small intestinal wall and into the hepatic portal vein.

ABSORPTION

Vitamins and minerals are absorbed. Note: Sugars and starches are members of the carbohydrate family.

LARGE INTESTINE: REABSORBING AND ELIMINATING Fluids and some minerals are absorbed. Some fibres from the seeds, whole-wheat bread, peanut butter and banana are partly digested by the bacteria living there, and some of these products are absorbed. Most fibres pass through the large intestine and are excreted as faeces; some fat, cholesterol and minerals bind to fibre and are also excreted.

EXCRETION

Chapter 3: Digestion, absorption and transport

75

FIGURE 3.8   Absorption of nutrients Carrier loads nutrient on outside of cell ...

Cell membrane

Carrier loads nutrient on outside of cell ...

En erg

... and then releases it on inside of cell.

Inside cell SIMPLE DIFFUSION

Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely.

FACILITATED TRANSPORT

Some nutrients (such as the water-soluble vitamins) are absorbed by facilitated transport. They need a specific carrier to transport them from one side of the cell membrane to the other. (Alternatively, facilitated transport may occur when the carrier changes the cell membrane in such a way that the nutrients can pass through.)

y

... and then releases it on inside of cell. ACTIVE TRANSPORT

Some nutrients (such as glucose and amino acids) are absorbed actively. These nutrients move against a concentration gradient, which requires energy.

small intestine engulfs and absorbs the nutrient molecules. To remove the molecules rapidly and provide room for more to be absorbed, a rush of circulating blood continuously washes the underside of this surface, carrying the absorbed nutrients away to the liver and other parts of the body. Figure 3.8 describes how nutrients are absorbed by simple diffusion, facilitated diffusion or active transport. Later chapters provide details on specific nutrients. Before following nutrients through the body, we must look more closely at the anatomy of the absorptive system.

Anatomy of the absorptive system If you have ever watched a sea anemone with its finger-like projections Absorption occurs at the inner surfaces of the GI tract, most in constant motion, you have a good picture of how the intestinal villi notably at the lining of the small intestine. The inner surface of move. the small intestine looks smooth and slippery, but when viewed through a microscope, it turns out to be wrinkled into hundreds of folds. Each fold is contoured into thousands of finger-like projections, as numerous as the hairs on velvet fabric. These small intestinal projections are the villi. A single villus, magnified still more, turns out to be composed of hundreds of cells, each covered with its own microscopic hairs, called the microvilli (see Figure 3.9). In the crevices between the villi lie the crypts – tubular glands that secrete the intestinal juices into the small intestine. Nearby, goblet cells secrete mucus. The villi are in constant motion. Each villus is lined by a thin sheet of muscle, so it can wave, squirm and wriggle like the tentacles of a sea anemone. Any nutrient molecule small enough to be absorbed is trapped among the microvilli that coat the cells and then drawn into the cells. Some partially digested nutrients are caught in the microvilli, digested further by enzymes there and then absorbed into the cells. The problem of food contaminants, which may be absorbed defencelessly by the The cells of the villi are among the most amazing in the body, for they recognise and select body, is the subject of the nutrients the body needs and regulate their absorption. As already described, each cell Chapter 19.

A closer look at the intestinal cells

Shutterstock.com/Windofchange64

Outside cell

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FIGURE 3.9   The small intestinal villi Stomach Folds with villi on them

Small intestine

The wall of the small intestine is wrinkled into thousands of folds and is carpeted with villi. Circular muscles

Science Photo Library/Eye of Science

Microvilli

Lymphatic vessel (lacteal)

Longitudinal muscles

Capillaries A villus Goblet cells

Crypts This is a photograph of part of an actual human intestinal cell with microvilli.

Each villus in turn is covered with even smaller projections, the microvilli. Microvilli on the cells of villi provide the absorptive surfaces that allow the nutrients to pass through to the body.

Artery Vein Lymphatic vessel

of a villus is coated with thousands of microvilli, which project from the cell’s membrane (review Figure 3.9). In these microvilli, and in the membrane, lie hundreds of different kinds of enzymes and ‘pumps’, which recognise and act on different nutrients. Descriptions of specific enzymes and ‘pumps’ for each nutrient are presented in the following chapters where appropriate; the point here is that the cells are equipped to handle all kinds and combinations of foods and nutrients.

Specialised cells A further refinement of the system is that the cells of successive portions of the intestinal tract are specialised to absorb different nutrients. The nutrients that are ready for absorption early are absorbed near the top of the GI tract; those that take longer to be digested are absorbed further down. Healthcare professionals who treat digestive disorders learn the specialised absorptive functions of different parts of the GI tract so that if one part becomes dysfunctional, the diet can be adjusted accordingly.

Chapter 3: Digestion, absorption and transport

APPLICATIONS OF NUTRITION RESEARCH The myth of ‘food combining’ The idea that people should not eat certain food combinations (e.g. fruit and meat) at the same meal because the digestive system cannot handle more than one task at a time, is a myth. The art of ‘food combining’ (which actually emphasises ‘food separating’) is based on this idea, and it represents faulty logic and a gross underestimation of the body’s capabilities. In fact, the contrary is often true; foods eaten together can enhance each other’s use by the body. For example, vitamin C in an orange or other citrus fruit can enhance the absorption of iron from a meal of chicken and rice or other iron-containing foods. Many other instances of mutually beneficial interactions are presented in later chapters.

Preparing nutrients for transport When a nutrient molecule has crossed the cell of a villus, it enters either the bloodstream or the lymphatic system. Both transport systems supply vessels to each villus, as shown in Figure 3.9. The water-soluble nutrients and the smaller products of fat digestion are released directly into the bloodstream and guided directly to the liver, where their fate and destination will be determined. The larger fats and the fat-soluble vitamins are insoluble in water, however, and blood is mostly water. The intestinal cells assemble many of the products of fat digestion into larger molecules. These larger molecules cluster together with special proteins, forming chylomicrons. Because chylomicrons carry fat, they are released into the lymphatic system. They move through the lymph until they can enter the bloodstream at a point near the heart, consequently bypassing the liver initially. (Chylomicrons are described in more detail further in this chapter and in Chapter 5.)

3.3  The circulatory systems

Once a nutrient has entered the bloodstream, it may be transported to any of the cells in the body, from the tips of the toes to the roots of the hair. The circulatory systems deliver nutrients wherever they are needed.

The vascular system The vascular, or blood circulatory, system is a closed system of vessels through which blood flows continuously, with the heart serving as the pump (see Figure 3.10). As the blood circulates through this system, it picks up and delivers materials as needed. All the body tissues derive oxygen and nutrients from the blood and deposit carbon dioxide and other wastes back into the blood. The lungs exchange carbon dioxide (which leaves the blood to be exhaled) and oxygen (which enters the blood to be delivered to all cells). The digestive system supplies the nutrients to be picked up. In the kidneys, wastes other than carbon dioxide are filtered out of the blood to be excreted in the urine. As shown in Figure 3.10, blood leaving the right side of the heart circulates through the lungs and then back to the left side of the heart. The left side of the heart then pumps the blood out of the aorta through arteries to all systems of the body. The blood circulates in the capillaries, where it exchanges material with the cells and then collects into veins, which return it again to the right side of the heart. In short, the simple route that blood travels is: • Heart to arteries to capillaries to veins to heart.

REVIEW IT

The many folds and villi of the small intestine dramatically increase its surface area, facilitating nutrient absorption. Nutrients pass through the cells of the villi and enter either the blood (if they are watersoluble or small fat fragments) or the lymph (if they are fat-soluble).

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FIGURE 3.10   The vascular system

Head and upper body

2 Blood loses carbon dioxide and picks up oxygen in the lungs and returns to the left side of the heart by way of the pulmonary vein.

Lungs

Pulmonary vein

2 Pulmonary artery

Aorta

1 Blood leaves the right side of the heart by way of the pulmonary artery.

Left side

1

7 Lymph from most of the body’s organs, including the digestive system, enters the bloodstream near the heart.

7

Hepatic vein

Right side

4 4 Blood may leave the aorta to go to the upper body and head; or

Heart Hepatic artery Hepatic portal vein

Liver

Digestive tract

6 Blood returns to the right side of the heart. 6

Blood may leave the aorta to go to the lower body. 5 5 Blood may go to the digestive tract and then the liver; or

Lymph Key: Arteries

3 Blood leaves the left side of the heart by way of the aorta, the main artery that launches blood on its course through the body.

3

Entire body

Blood may go to the pelvis, kidneys and legs.

Capillaries Veins Lymph vessels

The routing of the blood leaving the digestive system is a special feature. The blood is carried to the digestive system (as to all organs) by way of an artery, which (as in all organs) branches into capillaries to reach every cell. Blood leaving the digestive system, however, goes by way of a vein. The hepatic portal vein directs blood not back to the heart, but to another organ – the liver. This vein again branches into capillaries so that every cell of the liver has access to the blood. Blood leaving the liver then again collects into a vein, called the hepatic vein, which returns blood to the heart. The route is: • Heart to arteries to capillaries (in intestines) to hepatic portal vein to capillaries (in liver) to hepatic vein to heart. Figure 3.11 shows the liver’s key position in nutrient transport. The liver’s placement ensures that it will be first to receive the nutrients absorbed from the GI tract. In fact, the liver busily prepares carbohydrates, fats, proteins, and other absorbed nutrients for use by the rest of the body. Of all the body’s organs, the liver is the most metabolically active, as Chapter 7 describes. In addition, the liver defends the body by detoxifying substances that might cause harm and preparing waste products for excretion. This is why, when people ingest poisons that

Chapter 3: Digestion, absorption and transport

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FIGURE 3.11   The liver Hepatic vein Capillaries 1

Vessels gather up nutrients from the digestive tract. Not shown here: Parallel to these vessels (veins) are other vessels (arteries) that carry oxygen-rich blood from the heart to the intestines.

2

The vessels merge into the hepatic portal vein, which conducts all absorbed materials to the liver.

3

The hepatic artery brings a supply of freshly oxygenated blood (not loaded with nutrients) from the lungs to supply oxygen to the liver’s own cells.

4

A network of large capillaries branch all over the liver, making nutrients and oxygen available to all its cells and giving the cells access to blood from the digestive system.

5

The hepatic vein gathers up blood in the liver and returns it to the heart.

In contrast, nutrients absorbed into lymph do not go to the liver first. They go to the heart, which pumps them to all the body’s cells. The cells remove the nutrients they need, and the liver handles the remnants.

Hepatic artery

5 4

Hepatic portal vein 3

2

Vessels

1

succeed in passing the first barrier (the intestinal cells), the liver quite often suffers the damage; for example, from viruses, such as hepatitis; drugs, such as barbiturates or alcohol; toxins, such as pesticide residues; and contaminants, such as mercury. Perhaps, in fact, you have been undervaluing your liver, not knowing what heroic tasks it quietly performs for you.

The lymphatic system The lymphatic system provides a one-way route for fluid from the tissue spaces to enter the blood. Unlike the vascular system, the lymphatic system has no pump; instead, lymph circulates between the cells of the body and collects into tiny vessels. The fluid moves from one portion of the body to another as muscles contract and create pressure here and there. Ultimately, much of the lymph collects in the thoracic duct behind the heart. The thoracic duct opens into the subclavian vein, where the lymph enters the bloodstream. Thus, nutrients from the GI tract that enter lymphatic vessels (large fats and fat-soluble vitamins) ultimately enter the bloodstream, circulating through arteries, capillaries and veins like the other nutrients, with a notable exception – they bypass the liver. Once inside the vascular system, the nutrients can travel freely to any destination and can be taken into cells and used as needed. What becomes of them is described in later chapters.

The lymphatic vessels of the intestine that take up nutrients and pass them to the lymph circulation are called lacteals.

PUTTING COMMON SENSE TO THE TEST

Veins and lymphatic vessels leaving the digestive tract carry nutrients to the body. TRUE

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REVIEW IT

Nutrients leaving the digestive system via the blood travel directly to the liver before being transported to the body’s cells. Those leaving via the lymphatic system eventually enter the vascular system but bypass the liver at first.

3.4  The health and regulation of the GI tract

This section describes the bacterial populations and the hormonal and nerve regulation of a healthy GI tract. Highlight 3 presents common problems that may arise when normal GI function falters.

Shutterstock.com/New Africa

Gastrointestinal microbiome A healthy GI tract is home to a vibrant community of some 100 trillion microbes – bacteria, viruses, fungi, protozoa and other microorganisms, collectively known as the human microbiome. The microbiome is all the genes inside the microbial cells that create PUTTING COMMON SENSE the microbiota, which is the community of microorganisms themselves. The two terms of TO THE TEST microbiota and microbiome are often used to mean the same thing. The microbiome creates its own mini ecosystem in the same way that plants, animals and insects live together in their The gastrointestinal own delicate ecosystem in a rainforest. The entire microbiome in our GI tract weighs between tract is sterile 0.5 to 2 kilograms. One-third of our gut microbiome is common between most people, throughout. while two-thirds are specific to just you. This makes our gut microbiome as unique as our FALSE fingerprints. The gut microbiome is not a static thing. It changes throughout life after first colonising the gut shortly after birth and continuing to gather new members from the environment throughout life. Variation is highest during childhood, and it gradually decreases with age. Illness, antibiotic use, fever, stress, injury and dietary changes all affect the blend of microbes that make up the microbiome. The prevalence of different microbes in various parts of the GI tract depends on such factors as pH, peristalsis, diet and other microbes. Relatively few microbes can live in the low pH of the stomach with its somewhat rapid peristalsis, whereas the neutral pH and slow peristalsis of the lower small intestine and the large intestine permit the growth of a diverse and abundant population. Emerging research is revealing how a person’s health reflects the relative stability, disturbance and resilience of the microbiome.1 Changes in the gut microbiome composition and activity are associated with dozens of common diseases. Immunity, mental health, heart disease, diabetes, chronic inflammation and even body weight make up the fascinating areas covered in the ever-growing research field of the gut microbiome.2 Interestingly, similarities in microbiota composition are apparent in people who have the same disease, and differences are noted when their health status differs. For example, the number and kinds of GI microbes differ in non-obese and obese individuals; the population of microbes in obese people with more body fat and obesity-related diseases is less diverse than in non-obese people.3 Ongoing research is trying to determine exactly how the GI microbiota might contribute to the development of obesity and other metabolic diseases.4 The microbiome population and environment can change dramatically in response to diet – in both the short term (daily meals) and the long term (habitual diet patterns).5 In fact, one of the ways diet may help manage diseases is by changing the microbiota. Consider, for example, that the most recommended diet strategy to improve health – plant-based eating patterns – promotes Eaten regularly, yoghurt may alleviate common digestive problems. the most favourable changes in the GI microbiota.6 Such

Chapter 3: Digestion, absorption and transport

diets are high in fibres that cannot be digested by the human body but can provide a major source of energy for bacteria, fostering their growth. Fibre and some other food components are called prebiotics because they encourage the growth and activity of beneficial bacteria, such as Bifidobacteria and Lactobacillus. With a greater diversity of bacteria in the gut, they release more beneficial fermentation byproducts, such as short-chain fatty acids (SCFAs). These SCFAs are linked to a range of health benefits, including lowering the pH in the bowel, improving the bioavailability of calcium and magnesium, and inhibition of potentially harmful bacteria.7 SCFAs may also have a role in insulin sensitivity, energy expenditure, appetite regulation, and gene expression. Some other benefits of prebiotics include a stronger gut barrier, a well-functioning immune system and even regularity of bowel movements. Prebiotics can also help reduce the amount of potentially damaging bacteria in the gut by altering the acidity, making it a less hospitable place for the more harmful bacteria. Some foods contain probiotics, live microbes that change the conditions in the GI tract in ways that seem to benefit health. For example, yoghurt contains Lactobacillus and other living bacteria. But there are many other probiotic foods now being rediscovered, such as sauerkraut, kimchi, kefir, natto, sourdough bread and kombucha. The potential GI health benefits of probiotics or products of their metabolism include helping to alleviate diarrhoea, constipation, inflammatory bowel disease, ulcers, allergies, lactose intolerance and infant colic.8 Research studies continue to explore how diet influences GI bacteria and which foods – with their prebiotics and probiotics – affect GI health. In addition, research studies are beginning to reveal several health benefits beyond the GI tract, such as lowering blood cholesterol, blood pressure and inflammation responses.9 Bacteria in the GI tract also produce several vitamins, including biotin, folate, pantothenic acid, riboflavin, thiamin, vitamin B6, vitamin B12 and vitamin K. Because the amounts produced of these vitamins are insufficient to meet the body’s needs or in the case of vitamin B12 it cannot be absorbed in the colon where it is produced, these vitamins are nevertheless considered essential nutrients that must be provided by the diet.

HOW TO:

HOW TO KEEP YOUR GUT HEALTHY

To keep your gut ecosystem thriving, aim to eat more foods high in different types of fibre including soluble and insoluble fibre and resistant starch. Fibre is nourishment for gut bacteria, and you will find it in an array of everyday foods. The simplest advice is to eat a wide variety of nutritious whole foods from all food groups, which would naturally contain different types of fibre. Some of the key prebiotic and probiotic foods include: › Aromatic vegetables, such as onions, garlic, leeks, celery and Jerusalem artichokes. These foods are high in a type of carbohydrate called inulin, which bacteria use to promote healthy colon cells and other health benefits. › Barley and oats are a rich source of the soluble fibre beta-glucan, which acts as food for your good gut bacteria and helps lower cholesterol levels. › Starchy foods, such as cooked potatoes, beans and lentils and green bananas are high in resistant starch, which is resistant to digestive attack and passes through to the large intestine. Once there, the resistant starch is broken down and fermented by bacteria. › Fermented foods, such as sauerkraut, kimchi, kefir and yoghurt contain a good supply of healthy bacteria to add to your microbiome.

Diet, mental health and the gut microbiome A nutritious diet is not just good for your body. It is also good for your brain and mental health too, with a growing body of evidence linking an unhealthy dietary pattern to a greater risk of developing depression or anxiety.10 Initial work in mice showed that changes in the gut microbiota can go on to lead to depressive-like symptoms. Supplementing the diets of the stressed mice can reverse the problems. So, what is the case in humans then? People with depression do have a different gut microbe fingerprint compared to healthy volunteers.11 And

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intriguingly, human clinical trials involving probiotic supplementation appear to demonstrate an improvement in psychological symptoms related to depression, anxiety and stress.12 Mental health disorders, particularly depression, account for the highest burden of global disability. Depressive disorders affect almost 300 million people around the world and are associated with unemployment, poor physical health, impaired social functioning and, in its most severe forms, suicide.13 Counselling and medication gain most of the treatment attention for depression, but the promise of dietary changes in helping to improve the outlook of people with depression and other common conditions, such as anxiety, is gaining traction. The bidirectional communication between the central nervous system and the gut microbiota, referred to as the gut–brain axis, has been of significant interest in recent years. Poor diet, which can affect the microbial composition of the gut and cause systemic inflammation, has been linked to several mental illnesses including anxiety and depression as Figure 3.12 shows.14 There is now a growing research interest in seeing how dietary changes can affect mood disorders, with depression and anxiety as the main focus. A summary of the published intervention studies in the field finds dietary intervention is effective in having a small, but meaningful effect in lowering the symptoms of depression.15 There is no one single diet that

FIGURE 3.12   Diet has been linked with the risk of developing depression and anxiety. Because the gut microbiota communicate with the brain in a bidirectional manner and diet can influence the gut microbiota, the gut microbiota are likely a key part of our mental health Food choices Vitamins/minerals Omega-3 Phytochemicals

DEPRESSION/ANXIETY

typ e

Anti-inflammatory foods

DIETARY PATTERN

‘He alt hy ’

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et di

iet ed typ ’ n ter es ‘W

Inflammatory foods

Metabolites Vagus nerve

Autonomic nervous system

inflammation Gut permeability

Neurotransmitters Inflammation Fibre/gut motility Omega-3 Macronutrient ratios Food additives Phytochemicals

GUT MICROBIOTA

Prebiotics Adapted from T. L. K. Bear and co-authors, The role of the gut microbiota in dietary interventions for depression and anxiety, Advances in Nutrition, 11 (2020): 890–907.

Chapter 3: Digestion, absorption and transport

is deemed effective as there are many different approaches to eating healthier, however, a Mediterranean-style diet is of prominent interest. The mechanisms by which dietary changes might influence depression symptoms are unclear. Biochemical pathways involving inflammation, oxidative stress and mitochondrial dysfunction are all known to be disrupted in people with mental disorders, so diet could be having a positive impact. Then there is the growing realisation that gut microbes play an important part in stress responses, immune function and neurotransmission. Diet and mental health is a rapidly growing research field. We can expect more research to be undertaken into the link between healthy eating patterns and mental health.

CURRENT RESEARCH IN NUTRITION Healthier diet changes in adolescence improve depression outlook Interest in the link between nutrition and mental health is growing rapidly. There is now a small but growing field of research looking at diet change interventions in people with depression to see how this can improve their outlook. One such study investigated the link between diet and depression in young adults, which we will look at in more detail. 16 Adolescence and young adulthood are periods with an increased risk of depression. These are also critical periods for establishing healthy eating habits which can carry over into adulthood. The study involved 101 adults aged between 17 to 35 years, all who had moderate-to-high symptoms of depression. They all were considered to have a poor diet when assessed against Australian Government healthy eating guidelines. Participants were randomly allocated to either a diet change group or control group. The diet change group was given advice on improving their diet by having more fruits, vegetables, wholegrains, nuts, fish, legumes, eggs, tofu and lean meats according to the person’s individual dietary preferences. The control group received no advice on diet and were left to continue their normal habits for the three weeks the study ran. Those in the diet change group were indeed successful in making positive changes to their diet. With these diet changes, significant improvements in mood, depression and anxiety were all seen. No such changes were seen in the control group. Three months after the study finished, follow-up was made with 33 of the participants to see how they were tracking. One in five of those in the diet change group were keeping up with the healthy eating habits and for these people, their mood improvements stuck. This study adds more support for the benefits of positive dietary changes in improving mental health. Counselling, emotional support, and medications all have their role to play, and diet may be another element to consider in dealing with depression.

Gastrointestinal hormones and nerve pathways The ability of the digestive tract to handle its ever-changing contents routinely illustrates an important physiological principle that governs the way all living things function – the principle of homeostasis. Simply stated, survival depends on body conditions staying about the same; if they deviate too far from the norm, the body must act to bring them back to normal. The body’s regulation of digestion is one example of homeostatic regulation. The body also regulates its temperature, its blood pressure and all other aspects of its blood chemistry in similar ways. Two intricate and sensitive systems coordinate all the digestive and absorptive processes: the hormonal (or endocrine) system and the nervous system. Even before the first bite of food is taken, the mere thought, sight or smell of food can trigger a response from these systems. Then, as food travels through the GI tract, it either stimulates or inhibits digestive secretions by way of messages that are carried from one section of the GI tract to another by both hormones and nerve pathways. (See Appendix A for a brief summary of the body’s hormonal system and nervous system.)

In general, any gastrointestinal hormone may be called an enterogastrone, but the term refers specifically to any hormone that slows motility and inhibits gastric secretions.

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FIGURE 3.13   An example of a negative feedback loop Food in the stomach causes the cells of the stomach wall to start releasing gastrin.

Gastrin stimulates stomach glands to release the components of hydrochloric acid.

Stomach pH reaches 1.5 acidity.

The inactive precursor of an enzyme is called a proenzyme or zymogen: • pro = before • zym = concerning enzymes • gen = to produce.

Notice that the kinds of regulation described next are all examples of feedback mechanisms. A certain condition demands a response. The response changes that condition, and the change then cuts off the Acidity in the response. Thus, the system is self-correcting. The following are examples stomach causes the of this: cells of the • The stomach normally maintains a pH between 1.5 and 1.7. How stomach wall to stop releasing does it stay that way? Food entering the stomach stimulates cells gastrin. in the stomach wall to release the hormone gastrin. Gastrin, in turn, stimulates the stomach glands to secrete the components of hydrochloric acid. When a pH of 1.5 is reached, the acid itself turns off the gastrin-producing cells. They stop releasing gastrin and the glands stop producing hydrochloric acid. Thus, the system adjusts itself, as Figure 3.13 shows. • Nerve receptors in the stomach wall also respond to the presence of NEGATIVE food and stimulate the gastric glands to secrete juices and the muscles FEEDBACK to contract. As the stomach empties, the receptors are no longer stimulated, the flow of juices slows and the stomach quietens down. • The pyloric sphincter opens to let out a little chyme and then closes again. How does it know when to open and close? When the pyloric sphincter relaxes, acidic chyme slips through. The cells of the pyloric muscle on the intestinal side sense the acid, causing the pyloric sphincter to close tightly. Only after the chyme has been neutralised by pancreatic bicarbonate and the juices surrounding the pyloric sphincter have become alkaline can the muscle relax again. This process ensures that the chyme will be released slowly enough to be neutralised as it flows through the small intestine. This is important because the small intestine has less mucous coating than the stomach and so is not as well protected from acid. • As the chyme enters the intestine, the pancreas adds bicarbonate to it so that the intestinal contents always remain at a slightly alkaline pH. How does the pancreas know how much to add? The presence of chyme stimulates the cells of the duodenum wall to release the hormone secretin into the blood. When secretin reaches the pancreas, it stimulates the pancreas to release its bicarbonate-rich juices. Thus, whenever the duodenum signals that acidic chyme is present, the pancreas responds by sending bicarbonate to neutralise it. When the need has been met, the cells of the duodenum wall are no longer stimulated to release secretin, the hormone no longer flows through the blood, the pancreas no longer receives the message and it stops sending pancreatic juice. Nerves also regulate pancreatic secretions. • Pancreatic secretions contain a mixture of enzymes to digest carbohydrate, fat and protein. How does the pancreas know how much of each type of enzyme to provide? This is one of the most interesting questions physiologists have asked. Clearly, the pancreas does know what its owner has been eating, and it secretes enzyme mixtures tailored to handle the food mixtures that have been arriving recently (over the past several days). Enzyme activity changes proportionately in response to the amounts of carbohydrate, fat and protein in the diet. If a person has been eating mostly carbohydrates, the pancreas makes and secretes mostly carbohydrases; if the person’s diet has been high in fat, the pancreas produces more lipases; and so on. Presumably, hormones from the GI tract, secreted in response to meals, keep the pancreas informed about its digestive tasks. The day or two of lag between the time a person’s diet changes dramatically and the time digestion of the new diet becomes efficient explains why dietary changes can ‘upset digestion’ and should be made gradually. • Why don’t the digestive enzymes damage the pancreas? The pancreas protects itself from harm by producing an inactive form of the enzymes. It releases these proteins into the small intestine where they are activated to become enzymes. In pancreatitis, the digestive enzymes become active within the infected pancreas, causing inflammation and damage to the delicate pancreatic tissues.

Chapter 3: Digestion, absorption and transport

• When fat is present in the intestine, the gall bladder contracts to squirt bile into the intestine to emulsify the fat. How does the gall bladder get the message that fat is present? Fat in the intestine stimulates cells of the intestinal wall to release the hormone cholecystokinin (CCK). This hormone, travelling in the blood to the gall bladder, stimulates it to contract, releasing bile into the small intestine. Cholecystokinin also travels to the pancreas and stimulates it to secrete its juices, releasing bicarbonate and enzymes into the small intestine. Once the fat in the intestine is emulsified and enzymes have begun to work on it, the fat no longer provokes release of the hormone and the message to contract is cancelled. (Fat emulsification can continue even after a diseased gall bladder has been surgically removed because the liver can deliver bile directly to the small intestine.) • Fat and protein take longer to digest than carbohydrate does. When fat or protein is present, intestinal motility slows to allow time for its digestion. How does the intestine know when to slow down? Cholecystokinin is released in response to fat or protein in the small intestine. In addition to its role in fat emulsification and digestion, cholecystokinin slows GI tract motility. Slowing the digestive process helps to maintain a pace that allows all reactions to reach completion. Hormonal and nervous mechanisms like these account for much of the body’s ability to adapt to changing conditions. Table 3.2 summarises the actions of gastrin, secretin and cholecystokinin. These three hormones are among the most studied GI hormones, but the GI tract releases more than 20 hormones. In addition to assisting with digestion and absorption, many of these hormones regulate food intake and influence satiation. Current research is focusing on the roles these hormones may play in the development of obesity and its treatments. (More details are provided in Chapter 9.)

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Satiation is the feeling of satisfaction and fullness that occurs during a meal and that halts eating.

TABLE 3.2   The primary actions of selected GI hormones HORMONE

RESPONDS TO

SECRETED FROM

STIMULATES

RESPONSE

Gastrin

Food in the stomach

Stomach wall

Stomach glands

Hydrochloric acid secreted into the stomach to maintain an acidic pH

Secretin

Acidic chyme in the small intestine

Duodenal wall

Pancreas

Bicarbonate-rich juices secreted into the small intestine to maintain a slightly alkaline pH

Cholecystokinin

Fat or protein in the small intestine

Intestinal wall

Gall bladder Pancreas

Bile secreted into the duodenum to emulsify fats. Bicarbonate- and enzyme-rich juices secreted into the small intestine to maintain a slightly alkaline pH, digest fats and proteins and slow GI tract motility

The system at its best This chapter describes the anatomy of the digestive tract on several levels: the sequence of digestive organs, the cells and structures of the villi, and the selective machinery of the cell membranes. The intricate architecture of the digestive system makes it sensitive and responsive to conditions in its environment. Several different kinds of GI tract cells confer specific immunity against intestinal diseases, such as inflammatory bowel disease. In addition, secretions from the GI tract – saliva, mucus, gastric acid and digestive enzymes – not only help with digestion but also defend against many illnesses. One indispensable condition is good health of the digestive system itself. Like all the other organs of the body, the GI tract depends on a healthy supply of blood. The cells of the GI tract become weak and inflamed when blood flow is diminished, as may occur in heart disease when arteries become clogged or blood clots form. Just as a diminished blood flow to the heart or brain can cause a heart attack or stroke respectively, too little blood to the intestines can also be damaging – or even fatal. A diminished blood flow to the intestines – called intestinal ischaemia – is characterised by abdominal pain, forceful bowel movements, and blood in the stool.

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The health of the digestive system is also affected by such lifestyle factors as sleep, physical activity and state of mind. Adequate sleep allows for repair and maintenance of tissue and removal of wastes that might impair efficient functioning. Activity promotes healthy muscle tone. Stress alters GI motility, secretions, permeability, blood flow and bacteria. For healthy digestion, mealtimes should be relaxed and tranquil; pleasant conversations and peaceful environments during meals ease the digestive process. Another factor in GI health is the kind of foods eaten. Among the characteristics of meals that promote optimal absorption of nutrients are those mentioned in Chapter 2 – balance, moderation, variety and adequacy. Balance and moderation require having neither too much nor too little of anything. For example, too much fat can be harmful, but some fat is beneficial in slowing down intestinal motility and providing time for absorption of some of the nutrients that are slow to be absorbed. Variety is important for many reasons, but one is that some food constituents interfere with nutrient absorption. For example, some compounds common in high dietary fibre foods such as wholegrain cereals, certain leafy green vegetables, and legumes bind with minerals. To some extent, then, the minerals in those foods may become unavailable for absorption. These high-fibre foods are still valuable, but they need to be balanced with a variety of other foods that can provide the minerals. As for adequacy – in a sense, this entire book is about dietary adequacy. But here, at the end of this chapter, is a good place to emphasise the interdependence of the nutrients. It could almost be said that every nutrient depends on every other. All the nutrients work together, and all are present in the cells of a healthy digestive tract. To maintain health and promote the functions of the GI tract, you should make balance, moderation, variety and adequacy features of every day’s menus.

PUTTING COMMON SENSE TO THE TEST

The functions of the digestive tract are an example of the process of homeostasis. TRUE

REVIEW IT

A diverse and abundant bacteria population supports GI health. The regulation of GI processes depends on the coordinated efforts of the hormonal system and the nervous system. Together, digestion and absorption break down foods into nutrients for the body’s use. To function optimally, a healthy GI tract needs a balanced diet, adequate rest and regular physical activity

Chapter 3: Digestion, absorption and transport

CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Gastric juice has a pH similar to that of water and helps support bacterial growth in the stomach. FALSE

Gastric juice is very acidic because it contains hydrochloric acid, which helps with protein digestion and kills many of the bacteria in food.

2 The process of food digestion begins in the mouth and proceeds all the way into the large intestine. TRUE

Food digestion and absorption is a process that occurs right along the gastrointestinal tract.



Both veins and lymph vessels are important avenues of nutrient transport from the digestive tract.

4 The gastrointestinal tract is sterile throughout. FALSE

There are trillions of bacteria found throughout the gastrointestinal tract.

5 The functions of the digestive tract are an example of the process of homeostasis. TRUE

3 Veins and lymphatic vessels leaving the digestive tract carry nutrients to the body. TRUE

The digestive tract is regulated at many different levels, from endocrine to neural, to maintain its functions.

NUTRITION PORTFOLIO A healthy digestive system can adjust to almost any diet and can handle any combination of foods with ease: • Describe the physical and emotional environment that typically surrounds your meals, including how it affects you and how it might be improved. • Detail any GI discomforts you may experience regularly and include suggestions to alleviate or prevent their occurrence (see Highlight 3).

•

With a focus on good food sources of prebiotics and probiotics, list any changes you can make in your eating habits to promote overall gut health and a healthy gut microbiome.

4

What does the pancreas secrete to neutralise stomach acid in the small intestine?

STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1

a b c d 2

The secretions from the gall bladder. The product of microbe action on the small intestine. Partially digested food that travels through the intestinal tract. The chewed food that is swallowed.

5

Hydrolysis Sphincters Peristalsis Bowel movements

What is the main function of bile? a b c d

Emulsify fats Catalyse hydrolysis Slow protein digestion Neutralise stomach acidity

6

Bile Mucus Enzymes Bicarbonate

Where do the digestion and absorption of carbohydrate predominantly occur? a b c d

What are the muscular contractions that move food through the GI tract called? a b c d

3

a b c d

What is chyme?

Mouth Small intestine Stomach Large intestine

Where does nutrient absorption primarily occur? a b c d

Mouth Stomach Small intestine Large intestine

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What are the specialised cells that increase gastrointestinal tract absorption? a b c d

8

Pancreatic cells Villi Colonocytes Islet cells

Which nutrients leave the GI tract by way of the lymphatic system? a b c d

9

What coordinates digestion and absorption? a b c d

Pancreas and kidneys Liver and gall bladder Hormonal system and the nervous system Vascular system and the lymphatic system

10 What are gastrin, secretin and cholecystokinin examples of? a b c d

Water and minerals Proteins and minerals All vitamins and minerals Fats and fat-soluble vitamins

Crypts Enzymes Hormones Goblet cells

REVIEW QUESTIONS 1

Describe the challenges associated with digesting food and the solutions offered by the human body. (Section 3.1)

5

How is blood directed through the digestive system? Which nutrients enter the bloodstream directly? Which are first absorbed into the lymph? (Section 3.3)

2

Describe the path food follows as it travels through the digestive system. Summarise the muscular actions that take place along the way. (Section 3.1)

6

What role do gut microbes have in keeping us healthy? (Section 3.4)

7

3

Name five organs that secrete digestive juices. How do the juices and enzymes facilitate digestion? (Section 3.1)

Describe how the body coordinates and regulates the processes of digestion and absorption. (Section 3.4)

8

How does the composition of the diet influence the functioning of the GI tract? (Section 3.4)

•

Visit the Gastroenterological Society of Australia and highlight a section of the GI tract for further information: http://www.gesa.org.au For information on diseases of the GI tract, visit http:// www.gastro-info.co.nz and https://www.health.govt. nz/your-health/conditions-and-treatments/diseasesand-illnesses

4

Describe the problems associated with absorbing nutrients and the solutions offered by the small intestine. (Section 3.2)

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • View the resources section of The Gut Foundation: https://www.gutfoundation.com.au

•

Chapter 3: Digestion, absorption and transport

3.5 COMMON DIGESTIVE PROBLEMS The facts of anatomy and physiology presented in Chapter 3 permit easy understanding of some common problems that occasionally arise in the digestive tract. Food may slip into the air passages instead of the oesophagus, causing choking. Bowel movements may be loose and watery, as in diarrhoea, or painful and hard, as in constipation. Some people complain about belching, while others are bothered by intestinal gas. Sometimes people develop medical problems, such as an ulcer. This highlight describes some of the symptoms of these common digestive problems and suggests strategies for preventing them.

HIGHLIGHT

3

FIGURE H3.1   Normal swallowing and choking Tongue Food

Larynx rises Epiglottis closes over larynx

Oesophagus (to stomach) Trachea (to lungs)

Getty Images/iStock/Monkey Business Images

Swallowing. The epiglottis closes over the larynx, blocking entrance to the lungs via the trachea. The red arrow shows that food is heading down the oesophagus normally.

Healthy eating with some changes where needed can help avoid digestive problems.

Choking Sometimes a sip of a beverage or a tiny bit of food ‘slips down the wrong pipe’. The body’s first response is to cough, which quite often clears the passage. When someone is truly choking, however, food has slipped into the trachea and completely blocked the air passageways (see Figure H3.1). Thus the person cannot cough – or even breathe. Without oxygen, the person may suffer brain damage within five minutes or even die. For this reason, it is imperative that everyone learns to recognise the universal distress signals for choking and to act promptly. To help a person who is choking, it is important to call for assistance and get this assisting person to dial 000 in Australia or 111 in New Zealand and request an ambulance. Because the larynx is in the trachea and makes sounds only

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Choking. A choking person cannot speak or gasp because food lodged in the trachea blocks the passage of air. The red arrow points to where the food should have gone to prevent choking.

when air is pushed across it, a person choking will be unable to speak. For this reason, to help a person who is choking, first ask, ‘Can you speak?’ If the person is coughing, breathing adequately, or able to speak, do not interfere. If the person cannot speak or cough, take action. Bend the choking person forward and give four sharp blows with the heel of your palm between the shoulder blades. This technique is called lateral chest thrusts and is carried out by using the heel of your hand in an upward movement between the shoulder blades. If this is still unsuccessful, place the person on their side on floor and wait for an ambulance. This advice is generic, and, in all cases, knowledge of first aid and regular training can save lives. Almost any food can cause choking, although some are cited more often than others: chunks of meat, hot dogs, nuts, whole grapes, raw carrots, marshmallows, hard or sticky lollies, gum, popcorn and peanut butter. These foods are particularly difficult for young children to safely chew and swallow. Inhaled food is the major cause of choking. Always remain alert to the dangers of choking whenever young children are eating. To prevent choking, cut food into small pieces, chew thoroughly before swallowing, don’t talk or laugh with food in your mouth and don’t eat when breathing hard.

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Vomiting Vomiting can be a symptom of many different diseases or may arise in situations that upset the body’s equilibrium, such as air or sea travel. For whatever reason, the contents of the stomach are propelled up through the oesophagus to the mouth and expelled. Sometimes the muscular contractions will extend beyond the stomach and carry the contents of the duodenum, with its green bile, into the stomach and then up the oesophagus. Although certainly unpleasant and wearying for the nauseated person, vomiting is often not a cause for alarm. Vomiting is one of the body’s adaptive mechanisms to rid itself of something irritating. The best advice is to rest and drink small amounts of liquids as tolerated until the nausea subsides. If vomiting incurs such large losses of fluid as to cause dehydration, medical aid may be needed. As fluid is lost from the GI tract, the body’s other fluids redistribute themselves so that, eventually, fluid is taken from every cell of the body. Fluid leaving the cells is accompanied by salts that are essential to the life of the cells. Replacing salts and fluid is difficult if the vomiting continues, and intravenous feedings of saline and glucose may be necessary. Vomiting and dehydration are especially serious in infants, and a physician should be contacted without delay. Self-induced vomiting, such as occurs in bulimia nervosa, also has serious consequences. In addition to fluid and salt imbalances, repeated vomiting can cause irritation and infection of the pharynx, oesophagus and salivary glands; erosion of the teeth and gums; and dental caries. The oesophagus may rupture or tear, as may the stomach. Sometimes the eyes become red from pressure during vomiting. Bulimic behaviour reflects underlying psychological problems that require intervention. (Bulimia nervosa is discussed fully in Highlight 8.)

Diarrhoea Diarrhoea is characterised by frequent, loose, watery stools. Such stools indicate that the intestinal contents have moved too quickly through the intestines for fluid absorption to take place, or that water has been drawn from the cells lining the intestinal tract and added to the food residue. Like vomiting, diarrhoea can lead to considerable fluid and salt losses, but the composition of the fluids is different. Stomach fluids lost in vomiting are highly acidic, whereas intestinal fluids lost in diarrhoea are nearly neutral. When fluid losses require medical attention, correct replacement is crucial. Diarrhoea is a symptom of various medical conditions and treatments. It may occur abruptly in a healthy person as a result of infections (e.g. food poisoning) or as a side effect of medications. When used in large quantities, food

ingredients, such as the sugar alternative sorbitol and the fat alternative olestra, may also cause diarrhoea in some people. If a food is responsible, then that food must be omitted from the diet, at least temporarily. If medication is responsible, a different medicine, when possible, or a different form (injectable versus oral, for example) may alleviate the problem. Diarrhoea may also occur as a result of disorders of the GI tract, such as irritable bowel syndrome or colitis. Treatment for diarrhoea depends on cause and severity, but it always begins with rehydration. Mild diarrhoea may subside with simple rest and extra liquids (e.g. clear juices and soups) to replace fluid losses. If diarrhoea is bloody or if it worsens or persists – especially in an infant, young child, elderly person, or person with a compromised immune system – call a doctor. Severe diarrhoea can be life-threatening.

Irritable bowel syndrome Irritable bowel syndrome (IBS) is one of the most common GI disorders and is characterised by frequent or severe abdominal discomfort and disturbance in the motility of the GI tract.1 In most cases, GI contractions are stronger and last longer than normal, forcing intestinal contents through quickly and causing gas, bloating and diarrhoea. In some cases, however, GI contractions are weaker than normal, slowing the passage of intestinal contents and causing constipation. The exact cause of IBS is not known, but environmental factors, such as changes in routine, emotional stress, infection and diet, are all known to trigger an attack. These triggers seem to aggravate symptoms but not cause them. Dietary treatment depends on identifying and avoiding individual foods that aggravate symptoms, using probiotics, taking peppermint oil and eating small meals.2 Other treatments that may be effective include exercise; antispasmodic and antidiarrhoeal drugs for diarrhoea or fibre supplements and laxatives for constipation; and psychological and behavioural therapies to reduce stress. Emerging evidence suggests some benefit for IBS symptoms from diets that are free of gluten and low in a specific type of carbohydrates referred to as FODMAPs (i.e. fermentable oligosaccharides, disaccharides, monosaccharides and polyols).3 Chapter 4 describes these FODMAPs in more detail. FODMAPs can be poorly absorbed in some people, leading to their accumulation in the small intestine and passing into the large intestine. Once there, they can draw more water into the bowel which increases the chance of diarrhoea. FODMAPs can also increase gas production from their fermentation by colonic bacteria. These effects of FODMAPs in the bowel explain many of the symptoms reported in IBS.

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Chapter 3: Digestion, absorption and transport

Personal hygiene (e.g. regular hand washing with soap and water) and safe food preparation (as described in Chapter 19) are easy and effective steps to take in preventing diarrhoeal diseases.

Colitis People with colitis, an inflammation of the large intestine, may also suffer from severe diarrhoea, abdominal pain, and bloating. Depending on the cause, treatment generally focuses on rehydration and medication to control diarrhoea, abdominal pain, and inflammation. Some people find some relief by avoiding certain foods that tend to worsen symptoms – notably greasy foods, milk products, and foods high in fibre.

Coeliac disease Coeliac disease is an autoimmune disease characterised by inflammation of the small intestine that occurs in response to foods that contain gluten, a protein commonly found in wheat, barley, rye, and possibly oats. Coeliac disease affects around 1 per cent of the population. In people with coeliac disease, gluten triggers an immune system reaction in the small intestine that causes inflammation, which damages the villi and decreases nutrient absorption. Signs of malnutrition, such as anaemia, weak and brittle bones, and dermatitis, may become apparent. Common symptoms include abdominal pains, bloating and flatulence, weight loss and chronic diarrhoea, making it challenging to diagnose. An accurate diagnosis depends on results from a blood test and a biopsy of the small intestine. Treatment focuses on a gluten-free diet, which allows the small intestine to heal. A gluten-free diet must eliminate not only wheat, barley, rye and, most often, oats, but also many processed items made with these grains, such as bouillon cubes, hot dogs, gravies, salad dressings, soups and some dietary supplements. People with coeliac disease learn to read food labels and to ask specific questions at restaurants in order to determine what foods are gluten-free.

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Some people who do not test positive for coeliac disease seem to have similar symptoms that tend to diminish when on a gluten-free diet and return when gluten is reintroduced into the diet. These people may be described as having non-coeliac gluten sensitivity.4 Quite often, they tend to self-diagnose and self-treat, which presents a problem because a gluten-free diet interferes with an accurate diagnosis of coeliac disease. Whether the symptoms in non-coeliac gluten sensitivity are responding to gluten or FODMAPs in similar foods is unclear. The popularity of gluten-free diets and products has grown dramatically in recent years, in part because of noncoeliac gluten sensitivity. In addition, some consumers seem slightly confused and mistakenly believe that if a product is free of something, then that missing something must be bad. Another common misconception is that a gluten-free diet is a weight-loss diet. Despite claims that eliminating gluten from the diet helps with a variety of ailments, there is no evidence to suggest that a gluten-free diet is beneficial for the general population, and it may even have unintended consequences. Gluten-free products often have less protein and more sugar than similar products made with gluten.5

Constipation Like diarrhoea, constipation describes a symptom, not a disease. Each person’s GI tract has its own cycle of waste elimination, which depends on its owner’s health, the type of food eaten, when it was eaten and when the person takes time to defecate. What is normal for some people may not be normal for others. Some people have bowel movements three times a day; others may have them three times a week. The symptoms of constipation include straining during bowel movements, hard stools and infrequent bowel movements (fewer than three per week). Abdominal discomfort, headaches, backaches and flatulence sometimes accompany constipation. Often, a person’s lifestyle may cause constipation. Being too busy to respond to the defecation signal is a common complaint. If a person receives the signal to defecate and ignores it, the signal may not return for several hours. In the meantime, water continues to be withdrawn from the faecal matter, so when the person does defecate, the stools are dry and hard. In such a case, a person’s daily regimen may need to be revised to allow time to have a bowel movement when the body sends its signal. Although constipation usually reflects lifestyle habits, in some cases it may be a side effect of medication or reflect a medical problem, such as a bowel obstruction. If discomfort is associated with passing faecal matter, seek medical advice to rule out disease. Once this has been

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done, simple treatments, such as increased dietary fibre, fluids and exercise, are recommended before the use of medications. One dietary measure that may be appropriate is to increase dietary fibre to between 25 and 28 grams per day gradually over the course of a week or two. Dietary fibre found in fruits, vegetables and whole grains helps to prevent constipation by increasing faecal mass. In the GI tract, fibre attracts water, creating soft, bulky stools that stimulate bowel contractions to push the contents along. These contractions strengthen the intestinal muscles. The improved muscle tone, together with the water content of the stools, eases elimination, reducing the pressure in the rectal veins and helping to prevent haemorrhoids. (Chapter 4 provides more information on fibre’s role in maintaining a healthy colon and reducing the risks of colon cancer and diverticulitis.) Diverticulitis is a condition in which the intestinal walls develop bulges in weakened areas, most commonly in the colon (see Figure H3.2). These bulging pockets, known as diverticula, can worsen constipation, entrap faeces and become painfully infected and inflamed (diverticulitis). Treatment may require hospitalisation, antibiotics or surgery. Drinking plenty of water in conjunction with eating high-fibre foods also helps to prevent constipation. The increased bulk physically stimulates the upper GI tract, promoting peristalsis throughout. Similarly, physical activity improves the muscle tone and motility of the digestive tract. As little as 30 minutes of physical activity a day can help prevent or alleviate constipation. If these suggested changes in lifestyle or diet do not correct constipation, then a doctor might recommend the use of stool softeners, laxatives or mineral oil.

FIGURE H3.2   Diverticula in the colon Diverticula may develop anywhere along the GI tract, but they are most common in the colon.

Diverticula (plural)

Diverticulum (singular)

These products are best used for brief periods. If needed for extended times, they should be used under physician supervision. Frequent use of laxatives can lead to dependency and upset the body’s fluid, salt, and mineral balances. Mineral oil interferes with the absorption of fatsoluble vitamins. One potentially harmful but currently popular practice is colonic irrigation – the internal washing of the large intestine with a powerful enema machine. Such an extreme cleansing is not only unnecessary but can be hazardous, especially for those with a history of digestive diseases. Side effects may be relatively minor (cramping, abdominal pain, bloating, nausea and vomiting) or quite severe (infections, kidney failure, pancreatitis and heart failure), sometimes leading to death. Common problems include equipment contamination, electrolyte abnormalities and intestinal perforation.

Belching and flatulence Many people complain of problems that they attribute to excessive flatulence. For some, belching is the complaint. Others blame intestinal gas for abdominal discomforts and embarrassment.

Belching Belching results from swallowing air. Everyone swallows a little bit of air with each mouthful of food, but people who eat too quickly may swallow too much air. Ill-fitting dentures, carbonated beverages and chewing gum can also contribute to the swallowing of air with resultant belching. The best advice for belching seems to be to eat slowly, chew thoroughly and relax while eating.

Flatulence Although flatulence can be an embarrassing experience, it is quite normal. (People who experience painful bloating from malabsorption diseases, however, require medical treatment.) Healthy people expel several hundred millilitres of intestinal gas several times a day. Almost all (99%) of the gases expelled – nitrogen, oxygen, hydrogen, methane and carbon dioxide – are odourless. The remaining ‘volatile’ gases are the infamous ones. Foods that usually produce gas must be determined individually. The most common offenders are foods rich in the carbohydrates – sugars, starches and fibre. When partially digested carbohydrates reach the large intestine, bacteria digest them, giving off gas as a by-product. People can test foods suspected of forming gas by omitting them individually for a trial period to see if there is any improvement.

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Chapter 3: Digestion, absorption and transport

People troubled by flatulence need to determine which foods bother them and then eat those foods in moderation.

Gastro-oesophageal reflux Almost everyone has experienced heartburn at one time or another, usually soon after eating a meal. Medically known as gastro-oesophageal reflux, heartburn is the painful sensation a person feels behind the breastbone (sternum) when the lower oesophageal sphincter allows the stomach contents to reflux into the oesophagus (see Figure H3.3). This may happen if a person eats or drinks

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too much (or both). Tight clothing and even changes of position (lying down, bending over) can cause it, too, as can some medications and smoking. Weight gain and being overweight increase the frequency, severity and duration of heartburn symptoms. A defect of the sphincter muscle itself is also a possible, but less common, cause. If the heartburn is not caused by an anatomical defect, treatment is fairly simple. To avoid such misery in the future, the person needs to learn to eat less at a sitting, chew food more thoroughly and eat it more slowly. Additional strategies are presented in Table H3.1. People who overeat or eat too quickly are likely to suffer from indigestion. The muscular reaction of the stomach to unchewed lumps or to being overfilled may be so intense that it upsets normal peristalsis. When this happens, overeaters may taste the stomach acid and feel pain. Over-the-counter antacids and acid controllers may provide relief but should be used only infrequently for occasional heartburn; they may mask or cause problems if used regularly. If problems continue, people who suffer from frequent and regular bouts of heartburn and indigestion may need to see a physician, who can prescribe specific medication to control gastrooesophageal reflux. Without treatment, the repeated splashes of acid can severely damage the cells of the oesophagus, creating a condition known as Barrett’s oesophagus. At that stage, the risk of cancer in the oesophagus increases dramatically.6 To repeat, if symptoms persist, see a doctor – don’t self-medicate.

FIGURE H3.3   Gastro-oesophageal reflux Oesophagus Reflux Diaphragm Weakened lower oesophageal sphincter

Acidic stomach contents Stomach

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TABLE H3.1   Strategies to prevent or alleviate common GI problems GI PRODUCT

STRATEGIES

Choking

• Take small bites of food • Chew thoroughly before swallowing • Don’t talk or laugh with food in your mouth • Don’t eat when breathing hard

Diarrhoea

• Avoid strenuous activity • Rest • Drink fluids to replace losses • Call for medical help if diarrhoea persists

Constipation

• Eat a high-fibre diet • Drink plenty of fluids • Exercise regularly • Respond promptly to the urge to defecate

Belching

• Eat slowly • Chew thoroughly • Relax while eating

Intestinal gas/bloating

• Eat troublesome foods in moderation

Heartburn

• Eat small meals • Drink liquids between meals • Sit up while eating; elevate your head when lying down • Wait three hours after eating before lying down • Wait two hours after eating before exercising • Refrain from wearing tight-fitting clothing • Avoid foods, beverages and medications that aggravate your heartburn. Common irritants include foods that are fried or high in fat; chocolate and peppermint; coffee, alcoholic beverages, and carbonated beverages; mustard, ketchup and tomato sauces; acidic substances, such as vinegar, citrus juices and citrus fruits • Refrain from smoking cigarettes or using tobacco products • Lose weight if overweight • Take medicine as prescribed by your doctor

Ulcer

• Avoid coffee and caffeine- and alcohol-containing beverages • Avoid foods that aggravate your ulcer • Minimise aspirin, ibuprofen and naproxen use • Refrain from smoking cigarettes

Ulcers Ulcers are another common digestive problem. An ulcer is a lesion (a sore), and a peptic ulcer is a lesion in the lining of the stomach (gastric ulcers) or the duodenum of the small intestine (duodenal ulcers). The compromised lining is left unprotected and exposed to gastric juices, which can be painful. In some cases, ulcers can cause internal bleeding. If GI bleeding is excessive, iron deficiency may develop. Ulcers that perforate the GI lining can pose life-threatening complications. Many people believe that an ulcer is caused by stress or spicy foods, but this is not the case. The stomach lining in a healthy person is well protected by its mucous coat. What, then, causes ulcers to form? Three major causes of ulcers have been identified: bacterial infection with Helicobacter pylori (commonly abbreviated H. pylori); the use of certain anti-

inflammatory drugs, such as aspirin, ibuprofen and naproxen; and disorders that cause excessive gastric acid secretion. Most commonly, ulcers develop in response to H. pylori infection. This discovery was revolutionary as it had long been thought that no bacteria could live in the harsh acid environment of the stomach. Professor Robin Warren, a pathologist working at the Royal Perth Hospital, Western Australia, observed corkscrew-shaped bacteria in stomach samples he was examining. Despite his best efforts to convince colleagues and other scientists, it was a physician, Dr Barry Marshall, who took up the challenge and he, too became convinced that many patients with stomach ulcers could be cured with a simple treatment of common antibiotics. It was a long road, with the turning point coming late in 1981 when Warren and Marshall succeeded in culturing the microbes and Marshall took the bold step of drinking some of them. Within days he was suffering the first signs

Chapter 3: Digestion, absorption and transport

of stomach ulcers, and the rest is now history – Warren and Marshall received the Nobel Prize for Medicine in 2005. Today, the standard treatment involves antibiotics that tackle the offending H. pylori bacteria, in conjunction with changes to lifestyle and diet that routinely cause indigestion or pain. This may include avoiding coffee and caffeine- and alcohol-containing beverages. Both regular and decaffeinated coffee stimulate acid secretion and so aggravate existing ulcers. Ulcers and their treatments highlight the importance of not self-medicating when symptoms persist. People with H. pylori infection often take over-the-counter acid controllers to relieve the pain of their ulcers when, instead, they need physician-prescribed antibiotics. Suppressing gastric acidity not only fails to heal the ulcer, but also actually worsens inflammation during an H. pylori infection. Furthermore, H. pylori infection has been

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linked with stomach cancer, making prompt diagnosis and appropriate treatment essential.7

Summary Table H3.1 summarises strategies to prevent or alleviate common GI problems. Many of these problems reflect hurried lifestyles. For this reason, many of their remedies require that people slow down and take the time to eat leisurely; chew food thoroughly to prevent choking, heartburn and acid indigestion; rest until vomiting and diarrhoea subside; and heed the urge to defecate. In addition, people must learn how to handle life’s day-today problems and challenges without overreacting and becoming upset; learn how to relax, get enough sleep and enjoy life. Remember, ‘what’s eating you’ may cause more GI distress than what you eat.

HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1

What are the similarities and differences for strategies that would be most helpful in managing diarrhoea compared to constipation?

2

The demand for gluten-free products has increased dramatically over the past decade as gluten-free diets have gained in popularity. Although a gluten-free diet is the best treatment for people with coeliac disease, it has been adopted by millions of other people for a

variety of other reasons. Compare the energy, dietary fibre, added sugars, and saturated fat on the labels of two similar products – one wholegrain and the other gluten-free – and determine what benefits and risks might accompany a gluten-free diet for those with coeliac disease and for others. Which product would you now be more likely to buy? Why?

REFERENCES CHAPTER 1 2

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A. M. Valdes and co-authors, Role of the gut microbiota in nutrition and health, BMJ 361 (2018): k2179. R. K. Singh and co-authors, Influence of diet on the gut microbiome and implications for human health, Translational Medicine 15 (2017): 73. A. L. Komaroff, The microbiome and risk for obesity and diabetes, Journal of the American Medical Association 317 (2017): 355–356. E. LeChatelier and co-authors, Richness of human gut microbiome correlates with metabolic markers, Nature 500 (2013): 541–546. V. Partula and co-authors, Associations between usual diet and gut microbiota composition: Results from the Milieu Intérieur crosssectional study, American Journal of Clinical Nutrition 109 (2019): 1472–1483. S. J. D. O’Keefe, Plant-based foods and the microbiome in the preservation of health and prevention of disease, American Journal of Clinical Nutrition 110 (2019): 265–266. J. L. Carlson and co-authors, Health effects and sources of prebiotic dietary fiber, Current Developments in Nutrition 2 (2018): nzy005.

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J. Suez and co-authors, The pros, cons, and many unknowns of probiotics, Nature Medicine 25 (2019): 716–729. D. B. DiRienzo, Effect of probiotics on biomarkers of cardiovascular disease: Implications for heart-healthy diets, Nutrition Reviews 72 (2014): 18–29. T. L. K. Bear and co-authors, The role of the gut microbiota in dietary interventions for depression and anxiety, Advances in Nutrition 11 (2020): 890–907. R. A. H. Adan and co-authors, Nutritional psychiatry: Towards improving mental health by what you eat, European Neuropsychopharmacology 29 (2019): 1321–1332. L. Chao and co-authors, Effects of probiotics on depressive or anxiety variables in healthy participants under stress conditions or with a depressive or anxiety diagnosis: A meta-analysis of randomized controlled trials, Frontiers in Neurology 11 (2020): 421. World Health Organization, Depression. Available at https://www. who.int/health-topics/depression

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T. L. K. Bear and co-authors, The role of the gut microbiota in dietary interventions for depression and anxiety, Advances in Nutrition, 11 (2020): 890–907. J. Firth and co-authors, The effects of dietary improvement on symptoms of depression and anxiety: A meta-analysis of randomized controlled trials, Psychosomatic Medicine 81 (2019): 265–280.

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H. M. Francis and co-authors, A brief diet intervention can reduce symptoms of depression in young adults – A randomised controlled trial, PLoS One 14 (2019): e0222768.

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C. Elliott, The nutritional quality of gluten-free products for children, Pediatrics 142 (2018): e20180525. M. Clermont and G. W. Falk, Clinical guidelines update on the diagnosis and management of Barrett’s esophagus, Digestive Diseases and Sciences 63 (2018): 2122–2128. M. Venerito and co-authors, Gastric cancer: Epidemiology, prevention, and therapy, Helicobacter 23 (2018): e12518.

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A. C. Ford and co-authors, Irritable bowel syndrome, New England Journal of Medicine 376 (2017): 2566–2578. E. Dimidi and K. Whelan, Food supplements and diet as treatment options in irritable bowel syndrome, Neurogastroenterology & Motility (2020): e13951. J. Wang and co-authors, A low-FODMAP diet improves the global symptoms and bowel habits of adult IBS patients: a systematic review and meta-analysis, Frontiers in Nutrition 8 (2021): 683191. M. M. Leonard and co-authors, Celiac disease and nonceliac gluten sensitivity: A review, JAMA Network 318 (2017): 647–656.

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CHAPTER

4

THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE Nutrition in your life

Whether you are cramming for an exam or daydreaming about your next holiday, your brain needs carbohydrate to power its activities. Your muscles need carbohydrate to fuel their work, too, whether you are racing to get to class on time or enjoying a swim in the summer warmth. Where can you get carbohydrate? Are some foods healthier choices than others? As you will learn from this chapter, whole grains, vegetables, legumes and fruits naturally deliver ample carbohydrate and fibre with valuable vitamins and minerals and little fat. Milk products typically lack fibre, but they also provide carbohydrate along with an assortment of vitamins and minerals. PUTTING COMMON SENSE TO THE TEST Circle your answer

T F Complex carbohydrates are long chains of monosaccharides joined together. T F The majority of carbohydrate digestion occurs in the small intestine. T F People who suffer lactose intolerance must avoid all dairy foods. T F Fat, not glucose, fuels the majority of the body’s energy needs.

LEARNING OBJECTIVES 4.1 Identify the monosaccharides, disaccharides and polysaccharides common in nutrition by their chemical structures and major food sources. 4.2 Identify the three important monosaccharides and three important disaccharides in the human diet.

4.3 Identify the three types of polysaccharides important in nutrition. 4.4 Summarise carbohydrate digestion and absorption. 4.5 Explain how the body maintains its blood glucose concentration and what happens when blood glucose rises too high or falls too low. Nuts contain niacin, which is very useful for your digestion process. It can improve condition of the dermis

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4.6 Describe how added sugars can contribute to health problems. 4.7 Identify the three common types of alternative sweeteners and their chemical properties.

4.8 Identify the health benefits of, and recommendations for, starches and fibres. 4.9 Summarise the key scientific evidence behind some of the current controversies surrounding carbohydrates and their kilojoules.

A student, quietly studying a textbook, is unaware that within their brain cells, billions of glucose molecules are splitting to provide the energy to permit learning. Yet glucose provides nearly all of the energy the human brain uses daily. Similarly, a marathon runner, crossing the finish line in triumph, seldom gives credit to the glycogen fuel that is devoured to help finish the race. Yet, together, these two carbohydrates – glucose and its storage form, glycogen – provide about half of all the energy that muscles and other body tissues use. People eat very little glucose and glycogen directly from their foods. When they eat foods rich in carbohydrates, their bodies breakdown the carbohydrate to glucose for immediate energy and convert the remainder into glycogen for storage. All plant foods – whole grains, vegetables, legumes and fruits – provide carbohydrate. Dairy foods also provide carbohydrates. Many people mistakenly think of carbohydrates as ‘fattening’ and avoid them when trying to lose weight. Such a strategy may be helpful if the carbohydrates are the simple sugars contained within soft drinks, lollies and biscuits, but it is counterproductive if the carbohydrates are the complex carbohydrates of whole grains, vegetables and legumes. As the next section explains, not all carbohydrates are created equal.

FIGURE 4.1   Atoms and their bonds. The four main types of atoms found in nutrients are hydrogen (H), oxygen (O), nitrogen (N) and carbon (C) H

O

N

C

1

2

3

4

Each atom has a characteristic number of bonds it can form with other atoms. H H H

C

C

O

H

H H Notice that in this simple molecule of ethyl alcohol, each H has one bond, O has two and each C has four.

•  hex = six

REVIEW IT

Most of the monosaccharides important in nutrition are hexoses, simple sugars with six atoms of carbon and the formula C6H12O6

4.1  Chemical structure of carbohydrates

The dietary carbohydrate family includes the simple carbohydrates (the sugars) and the complex carbohydrates (the starches and fibre). The simple carbohydrates are those that are described as monosaccharides (single sugars) and disaccharides (sugars composed of pairs of monosaccharides). The complex carbohydrates are polysaccharides – large molecules composed of chains of monosaccharides. Each atom can form a certain number of chemical bonds with other atoms: carbon atoms can form four bonds, nitrogen atoms can form three, oxygen atoms can form two, and hydrogen atoms can only form one. Carbohydrate bonds are represented as lines between the chemical symbols (e.g. C, N, O and H) that stand for the atoms (see Figure 4.1). Atoms form molecules in ways that satisfy the bonding requirements of each atom. Figure 4.1 includes the structure of ethyl alcohol, the active ingredient of alcoholic beverages, as an example. The two carbons each have four bonds represented by lines, the oxygen has two, and each hydrogen has one bond connecting it to other atoms. Chemical structures bond according to these rules as dictated by nature.

The carbohydrates are made of carbon (C), oxygen (O) and hydrogen (H). Each of these atoms can form a specified number of chemical bonds: carbon forms four, oxygen forms two and hydrogen forms one.

4.2  The simple carbohydrates

The following list of the most important simple carbohydrates in nutrition symbolises them as hexagons and pentagons of different colours. Three are monosaccharides: • glucose • fructose • galactose

Chapter 4: The carbohydrates: sugars, starches and dietary fibre

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Three are disaccharides: • maltose (glucose + glucose) • sucrose (glucose + fructose) • lactose (glucose + galactose) To understand the structure of carbohydrates, look at the units of which they are made. The monosaccharides most important in nutrition each contain 6 carbon atoms, 12 hydrogens and 6 oxygen atoms (written in shorthand as C6H12O6). Fructose is shown as a FIGURE 4.2  Chemical pentagon, but like the other monosaccharides, it has six carbons (as you will see in structure of glucose Figure 4.4).

Monosaccharides The three monosaccharides important in nutrition all have the same numbers and kinds of atoms, but in different arrangements. These chemical differences account for the differing sweetness of the monosaccharides. A pinch of purified glucose on the tongue gives only a mild sweet flavour, and galactose hardly tastes sweet at all. Fructose, however, is as intensely sweet as honey and, in fact, is the sugar primarily responsible for honey’s sweetness.

On paper, the structure of glucose has to be drawn flat, but in nature the five carbons and oxygen are roughly in a plane. The atoms attached to the ring carbons extend above and below the plane. H H H

Glucose

Chemically, glucose is a larger and more complicated molecule than the ethanol H (alcohol) shown in Figure 4.1, but it obeys the same rules of chemistry: each carbon atom has four bonds; each oxygen, two bonds; and each hydrogen, one bond. Figure 4.2 illustrates the chemical structure of a glucose molecule. The diagram of a glucose molecule shows all the relationships between the atoms and proves simple on examination, but there is an even simpler way to depict chemical structures. Figure 4.3 presents the chemical structure of glucose in a more simplified way by combining or omitting several symbols – yet it conveys the same information. Commonly known as blood sugar, glucose serves as an essential energy source for all the body’s activities. Its significance to nutrition is tremendous. Later sections explain that glucose is one of the two sugars in every disaccharide and the unit from which the majority of polysaccharides are made. One of these polysaccharides, starch, is the chief food source of energy for all the world’s people; another, glycogen, is an important storage form of energy in the body. Glucose reappears frequently throughout this chapter and all those that follow.

C O

C

O

C

H O

H

H O

H

C

H

C

C

H

O

O

H

H

Fructose

Fructose is the sweetest of the sugars. Curiously, fructose has exactly the same chemical formula as glucose – C6H12O6 – but its structure differs (see Figure 4.4). The arrangement of

FIGURE 4.3   Simplified diagrams of glucose CH2OH O H H H OH H HO OH H

OH

The lines representing some of the bonds and the carbons at the corners are not shown.

CH2OH O HO

OH

C C OH

OH Now the single hydrogens are not shown, but lines still extend upwards or downwards from the ring to show where they belong.

O

C

C C

C

Another way to look at glucose is to notice that its six carbon atoms are all connected.

In this and other illustrations throughout this book, glucose is represented as a blue hexagon.

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the atoms in fructose stimulates the taste buds on the tongue to produce the sweet sensation. Fructose occurs naturally in fruits and honey; other sources include products such as some soft drinks, ready-to-eat cereals and desserts, particularly those imported into Australia and New Zealand that have been sweetened with high-fructose corn syrup (HFCS; defined in Table 4.1, which appears later in the chapter under section 4.6 Health effects and recommended intakes of sugars).

Galactose

The monosaccharide galactose occurs naturally as a single sugar in only a few foods. Galactose has the same numbers and kinds of atoms as glucose and fructose in yet another arrangement. Figure 4.5 shows galactose beside a molecule of glucose for comparison.

FIGURE 4.4   Two monosaccharides: glucose and fructose

FIGURE 4.5   Two monosaccharides: glucose and galactose

Can you see the similarities? If you learnt the rules in Figure 4.3, you will be able to ‘see’ 6 carbons (numbered), 12 hydrogens (those shown plus one at the end of each single line) and 6 oxygen atoms in both these compounds. 6

CH2OH 5

4 HO

OH 3

2

1

5

1 OH

OH Glucose

CH2OH

O

6 HOCH2

O

Notice the similarities and the difference (highlighted in red) between glucose and galactose. Both have 6 carbons, 12 hydrogens and 6 oxygens, but the position of one OH group differs slightly.

HO 4 OH

CH2OH O

O

CH2OH

HO

2 OH

OH

HO

OH

OH

OH

3

OH

Fructose

OH Galactose

Glucose

Disaccharides The disaccharides are pairs of the three monosaccharides just described. Glucose occurs in all three; the second member of the pair is either fructose, galactose or another glucose. These carbohydrates – and all the other energy nutrients – are put together and taken apart by similar chemical reactions: condensation and hydrolysis.

Condensation

To make a disaccharide, a chemical reaction known as condensation links two monosaccharides together (see Figure 4.6). A hydroxyl (OH) group from one iStock.com/Ivan Bajic

FIGURE 4.6   Condensation of two monosaccharides to form a disaccharide CH2OH O HO Fruits package their simple sugars with fibre, vitamins and minerals, making them a sweet and healthy snack.

OH

CH2OH O OH

H

O

OH

OH

CH2OH O OH

OH H2O Water

Glucose + glucose An OH group from one glucose and an H atom from another glucose combine to create a molecule of H2O.

HO

CH2OH O

OH

OH OH

O +

OH OH

H2O Water Maltose The two glucose molecules bond together with a single O atom to form the disaccharide maltose.

Chapter 4: The carbohydrates: sugars, starches and dietary fibre

monosaccharide and a hydrogen atom (H) from the other combine to create a molecule of water (H2O). The two originally separate monosaccharides link together with a single oxygen (O).

Hydrolysis

To break a disaccharide in two, a chemical reaction known as hydrolysis occurs (see Figure 4.7). A molecule of water splits to provide the H and OH needed to complete the resulting monosaccharides. Hydrolysis reactions commonly occur during digestion.

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Reminder: A hydrolysis reaction splits a molecule into two, with H added to one and OH to the other (from water); Chapter 3 explained that hydrolysis reactions break down molecules during digestion.

FIGURE 4.7   Hydrolysis of a disaccharide

HO

OH

CH2OH O OH

OH

O Water H OH

CH2OH O OH

OH

HO

CH2OH O +

OH

OH

HO

OH

OH

OH OH Polara Studios, Inc.

CH2OH O

Bond broken

Bond broken Maltose

Glucose + glucose

The disaccharide maltose splits into two glucose molecules with H added to one and OH to the other (from the water molecule).

Maltose

The disaccharide maltose consists of two glucose units. Maltose is produced whenever starch breaks down – as happens in humans during carbohydrate digestion. It also occurs during the fermentation process that yields alcohol. Maltose is only a minor constituent of a few foods, most notably barley.

Major sources of starch include grains (e.g. rice, wheat, millet, rye, barley and oats), legumes (e.g. kidney beans, cannellini beans, peas, chickpeas and lentils), tubers (e.g. potatoes) and root crops (e.g. sweet potato and cassava).

Sucrose

Fructose and glucose together form sucrose. Because the fructose is accessible to the taste receptors, sucrose tastes sweet, accounting for some of the natural sweetness of fruits, some vegetables and grains. To make table sugar, sucrose is refined from the juices of sugar cane and then granulated. Depending on the extent to which it is refined, the product becomes the familiar brown, white and powdered sugars available at supermarkets.

Lactose

The combination of galactose and glucose makes the disaccharide lactose, the principal carbohydrate of milk. Known as milk sugar, lactose contributes half of the energy (kilojoules) provided by fat-free milk. REVIEW IT

Six simple carbohydrates, or sugars, are important in nutrition. The three monosaccharides – glucose, fructose and galactose – all have the same chemical formula (C6H12O6), but their structures differ. The three disaccharides – maltose, sucrose and lactose – are pairs of monosaccharides, each containing a glucose paired with one of the three monosaccharides. These sugars derive primarily from plants, except for lactose and its component galactose, which come from milk and milk products. Two monosaccharides can be linked together by a condensation reaction to form a disaccharide and water. A disaccharide, in turn, can be broken into its two monosaccharides by a hydrolysis reaction using water.

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4.3  The complex carbohydrates

In contrast to the simple sugars just mentioned, complex carbohydrates contain many glucose units and, in some cases, a few other monosaccharides strung together as, first, oligosaccharides and, second, as the larger polysaccharides. Three types of polysaccharides are important in nutrition: glycogen, starches and fibre. Glycogen is a storage form of energy in the animal body; starches play that role in plants; and fibre provides structure in stems, trunks, roots, leaves and skins of plants. Both glycogen and starch are built of glucose units. Fibre is composed of a variety of monosaccharides and other carbohydrate derivatives.

Glycogen Glycogen is found to only a limited extent in meats and not at all in plants (glycogen in animal muscles rapidly hydrolyses after slaughter). For this reason, food is not a significant source of glycogen. However, glycogen does perform an important role in the body. The human body stores glucose as glycogen – many glucose molecules linked together in highly branched chains (see the left-hand side of Figure 4.8). This arrangement permits rapid hydrolysis. When the hormonal message ‘release energy’ arrives at the glycogen storage sites in a liver or muscle cell, enzymes respond by attacking the many branches of glycogen simultaneously, making a surge of glucose available. Normally, only liver cells can produce glucose from glycogen to be sent directly to the blood; muscle cells can also produce glucose from glycogen but must use it themselves. Muscle cells can restore the blood glucose level indirectly, however, as Chapter 7 explains. FIGURE 4.8   Glycogen and starch molecules compared (small segments) Notice that the more highly branched the structure, the greater the number of ends from which glucose can be released. (These units would have to be magnified millions of times to appear at the size shown in this figure. For details of the chemical structures, see Appendix C.)

Glycogen A glycogen molecule contains hundreds of glucose units in highly branched chains. Each new glycogen molecule needs a special protein for the attachment of the first glucose (shown here in red).

Starch (amylopectin)

Starch (amylose)

A starch molecule contains hundreds of glucose molecules in either occasionally branched chains (amylopectin) or unbranched chains (amylose).

Starches The human body stores glucose as glycogen, but plant cells store glucose as starches – long, branched or unbranched chains of hundreds or thousands of glucose molecules linked together (see the middle and right-hand side of Figure 4.8). These giant starch molecules are packed side by side in grains, such as wheat or rice; in root crops and tubers, such as sweet potatoes and potatoes; and in legumes, such as lentils and beans. When you

Chapter 4: The carbohydrates: sugars, starches and dietary fibre

eat the plant, your body hydrolyses the starch to glucose and uses the glucose for its own energy purposes. All starchy foods come from plants. Grains are the richest food source of starch, providing much of the food energy for people all over the world – rice in Asia; wheat in Australia, New Zealand, US and Europe; corn in much of Central and South America; and millet, rye, barley and oats elsewhere. Legumes and tubers are also important sources of starch.

Fibre Dietary fibre is the structural part of plants and thus is found in all plant-derived foods – vegetables, fruits, whole grains and legumes. Most dietary fibre is made up of polysaccharides. As mentioned earlier, starches are also polysaccharides, but dietary fibre differs from starches in that the bonds between their monosaccharides cannot be broken down by digestive enzymes in the body. For this reason, dietary fibres are often described as non-starch polysaccharides. The non-starch polysaccharide fibres include cellulose, hemicelluloses, pectins, gums and mucilages. Fibres also include some non-polysaccharides such as lignins, cutins and tannins. Figure 4.9 illustrates the difference in the bonds that link glucose molecules together in starch with those found in the fibre cellulose. Because dietary fibre passes through the body, it contributes no monosaccharides, and therefore little or no energy. Even though most foods contain a variety of fibre, researchers often sort dietary fibre into two groups according to their solubility – soluble and insoluble fibre. Such distinctions help to explain their actions in the body.

Soluble fibre

Some dietary fibre dissolves in water (soluble fibre), forms gels (viscous) and is easily digested by bacteria in the colon (fermentable). Commonly found in oats, barley, legumes and citrus fruits, soluble fibre is most often associated with protecting against heart disease and diabetes by lowering blood cholesterol and glucose levels, respectively.1

Insoluble fibre

Other fibre does not dissolve in water (insoluble fibre), does not form gels (nonviscous) and is less readily fermented. Found mostly in whole grains (bran) and vegetables, insoluble fibre promotes bowel movements and alleviates constipation.

PUTTING COMMON SENSE TO THE TEST

Complex carbohydrates are long chains of monosaccharides joined together. TRUE

Dietary fibre occurs naturally in intact plants. Functional fibre is sometimes used as a term to describe fibre that has been extracted from plants or manufactured and has beneficial effects in human beings. In manufactured foods, total fibre is the sum of dietary fibre and functional fibre.

FIGURE 4.9   Starch and cellulose molecules compared (small segments) The bonds that link the glucose molecules together in cellulose are different from the bonds in starch (and glycogen). Human enzymes cannot digest cellulose. See Appendix C for chemical structures and descriptions of linkages.

Resistant starches

A few starches are also classified as dietary fibre. Known as resistant starches, these starches escape digestion and absorption in the small intestine. Starch may resist digestion for several reasons, including the individual’s efficiency in digesting starches and the food’s physical properties. Resistant starch is common in whole legumes, raw potatoes and unripe bananas.

Phytic acid

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Although not classified as a dietary fibre, phytic acid is often found accompanying them in the same foods. Because of this close association, researchers have been unable to determine whether it is the dietary fibre, the phytic acid or both that binds with minerals, preventing their absorption. This binding presents a risk of mineral deficiencies, but the risk is minimal when total fibre intake is reasonable and mineral intake adequate. The nutritional consequences of such mineral losses are described further in Chapters 12 and 13.

Starch

Cellulose

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REVIEW IT

Complex carbohydrates are the polysaccharides (chains of monosaccharides): glycogen, starches and dietary fibre. Both glycogen and starch are storage forms of glucose – glycogen in the body, and starch in plants – and both yield energy for human use. Dietary fibre also contains glucose (and other monosaccharides), but its bonds cannot be broken by human digestive enzymes, so it yields little, if any, energy. The accompanying table summarises the carbohydrate family of compounds.

The Carbohydrate Family SIMPLE CARBOHYDRATES (SUGARS)

COMPLEX CARBOHYDRATES

Monosaccharides: • glucose • fructose • galactose

Polysaccharides: • glycogen* • starches • fibres

Disaccharides: • maltose • sucrose • lactose * Glycogen is a complex carbohydrate (a polysaccharide) but not a dietary source of carbohydrate.

4.4  Digestion and absorption of carbohydrates The ultimate goal of digestion and absorption of sugars and starches is to break them into small molecules – chiefly glucose – that the body can absorb and use. The large starch molecules require extensive breakdown; the disaccharides need only be broken once, and the monosaccharides not at all. The initial splitting begins in the mouth; the final splitting and absorption occur in the small intestine; and conversion to glucose takes place in the liver.

iStock.com/Peopleimages

Carbohydrate digestion Figure 4.10 traces the digestion of carbohydrates through the gastrointestinal (GI) tract. When a person eats foods containing starch, enzymes hydrolyse the long chains to shorter chains, the short chains to disaccharides and, finally, the disaccharides to monosaccharides. This process begins in the mouth.

In the mouth In the mouth, thoroughly chewing high-fibre foods slows eating and stimulates the flow of saliva. The salivary enzyme amylase starts to work, When a person eats carbohydrate-rich foods, the hydrolysing starch to shorter polysaccharides and to the disaccharide maltose. body receives a valuable commodity – glucose. In fact, you can taste the change if you hold a piece of starchy food like a dry biscuit in your mouth for a few minutes without swallowing it – the dry The short chains of biscuit begins tasting sweeter as the enzyme acts on it. Because food is in the mouth for glucose units that result only a short time, very little carbohydrate digestion takes place there; it begins again in from the breakdown the small intestine once it passes through the stomach. of starch are known as dextrins. The word In the stomach sometimes appears on The swallowed bolus mixes with the stomach’s acid and protein-digesting enzymes, which food labels because dextrins can be used inactivate salivary amylase. Thus the role of salivary amylase in starch digestion is relatively as thickening agents in minor. To a small extent, the stomach’s acid continues breaking down starch, but its juices processed foods. contain no enzymes to digest carbohydrate. Dietary fibre lingers in the stomach and delays gastric emptying, thereby providing a feeling of fullness and satiety. Reminder: A bolus is a portion of food swallowed at one time.

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FIGURE 4.10   Carbohydrate digestion in the GI tract STARCH

DIETARY FIBRE

Mouth and salivary glands The salivary glands secrete saliva into the mouth to moisten the food. The salivary enzyme amylase begins digestion: Starch

Amylase

Small polysaccharides, maltose

Mouth The mechanical action of the mouth crushes and tears dietary fibre in food and mixes it with saliva to moisten it for swallowing. Salivary glands

Mouth

Stomach Stomach Stomach acid inactivates salivary enzymes, halting starch digestion.

(Liver)

Stomach Dietary fibre is not digested, and it delays gastric emptying.

(Gall bladder)

Small intestine and pancreas The pancreas produces an amylase that is released through the pancreatic duct into the small intestine:

Starch

Pancreatic amylase

Small polysaccharides, maltose

Then disaccharidase enzymes on the surface of the small intestinal cells hydrolyse the disaccharides into monosaccharides: Glucose Maltose Maltase + Glucose Sucrose

Lactose

Sucrase

Lactase

Pancreas

Fructose + Glucose Galactose + Glucose

Intestinal cells absorb these monosaccharides.

Small intestine Dietary fibre is not digested, and it delays absorption of other nutrients.

Small intestine Large intestine

Large intestine Most dietary fibre passes intact through the digestive tract to the large intestine. Here, bacterial enzymes digest dietary fibre: Some Bacterial Short-chain dietary enzymes fatty acids, fibre gas Dietary fibre holds water; regulates bowel activity; and binds substances such as bile, cholesterol and some minerals, carrying them out of the body.

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Understanding Nutrition

In the small intestine The small intestine performs most of the work of carbohydrate digestion. A major carbohydrate-digesting enzyme, pancreatic amylase, enters the intestine via the pancreatic duct and continues breaking down the polysaccharides to shorter glucose chains and maltose. The final step takes place on the outer membranes of the intestinal cells. There, specific enzymes break down specific disaccharides: • Maltase breaks maltose into two glucose molecules. • Sucrase breaks sucrose into one glucose and one fructose molecule. • Lactase breaks lactose into one glucose and one galactose molecule. At this point, all polysaccharides and disaccharides have been broken down to monosaccharides – mostly glucose molecules, with some fructose and galactose molecules as well.

Reminder: In general, the word ending -ase identifies an enzyme, and the beginning of the word identifies the molecule that the enzyme works on.

In the large intestine Within one to four hours after a meal, all the sugars and most of the starches have been digested. Only the dietary fibre remains in the digestive tract. Dietary fibre in the large intestine attracts water, which softens the stools for passage without straining. Also, bacteria in the GI tract ferment some dietary fibre. This process generates water, gas and short-chain fatty acids (described in Chapter 5). The colon uses these small fat molecules for energy. Metabolism of short-chain fatty acids also occurs in the cells of the liver. Dietary fibre, therefore, can contribute some energy (6 to 10 kilojoules per gram), depending on the extent to which it is broken down by bacteria and the fatty acids are absorbed.

Starches and sugars are called available carbohydrates because human digestive enzymes break them down for the body’s use. In contrast, dietary fibre is called unavailable carbohydrate because human digestive enzymes cannot break the bonds.

Carbohydrate absorption Glucose is unique in that it can be absorbed, to some extent through the lining of the mouth, but for the most part, nutrient absorption takes place in the small intestine. Glucose and galactose traverse the cells lining the small intestine by active transport; fructose is absorbed by facilitated diffusion, which slows its entry and produces a smaller rise in blood glucose. Likewise, unbranched chains of starch are digested slowly and produce a smaller rise in blood glucose than branched chains, which have many more places for enzymes to attack and release glucose rapidly. As the blood from the intestines circulates through the liver, cells there take up fructose and galactose and convert them to other compounds, most often to glucose, as shown in Figure 4.11. Thus, all disaccharides provide at least one glucose molecule directly, and they can provide another one indirectly – through the conversion of fructose and galactose to glucose.

The short-chain fatty acids produced by GI bacteria are primarily acetic acid, propionic acid and butyric acid.

The majority of carbohydrate digestion occurs in the small intestine. TRUE

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PUTTING COMMON SENSE TO THE TEST

To digest and absorb carbohydrates, the body breaks down starches into the disaccharide maltose. Maltose and the other disaccharides (lactose and sucrose) from foods are broken down into monosaccharides. Monosaccharides are then converted mostly to glucose to provide energy for the cells’ work. Dietary fibre helps to regulate the passage of food through the GI system and slows the absorption of glucose, but dietary fibre contributes little, if any, energy.

Chapter 4: The carbohydrates: sugars, starches and dietary fibre

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FIGURE 4.11   Absorption of monosaccharides 1 Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi.

3 In the liver, galactose and fructose are converted to glucose. Small intestine

Key: Glucose 2 Monosaccharides travel to the liver via the portal vein.

Fructose Galactose

Lactose intolerance Normally, the intestinal cells produce enough of the enzyme lactase to ensure that the disaccharide lactose found in milk is both digested and absorbed efficiently. Lactase activity is highest immediately after birth, important for an infant whose first and only food for a while will be breast milk or infant formula. In the great majority of the world’s populations, lactase activity declines dramatically during childhood and adolescence to about 5–10 per cent of the activity at birth. Only a relatively small percentage (about 30 per cent) of the people in the world retain enough lactase to digest and absorb lactose efficiently throughout adult life.

Symptoms When more lactose is consumed than the available lactase can handle, lactose molecules remain in the intestine undigested, attracting water and causing bloating, abdominal discomfort and diarrhoea – the symptoms of lactose intolerance. The undigested lactose becomes food for intestinal bacteria, which multiply and produce irritating acid and gas, further contributing to the discomfort and diarrhoea.

Causes

Lactase activity commonly declines with age. Lactase deficiency may also develop when the intestinal villi are damaged by disease, certain medicines, prolonged diarrhoea, or malnutrition. Depending on the extent of the intestinal damage, lactose malabsorption may be temporary or permanent. In extremely rare cases, an infant is born with a lactase deficiency.

Prevalence The prevalence of lactose intolerance varies widely among ethnic groups, indicating that the trait is genetically determined. The prevalence of lactose intolerance is lowest among Scandinavians and other northern Europeans and highest among native North Americans and South-East Asians.

Estimated prevalence of lactose intolerance: • >80% South-East Asians • 80% Native Americans • 75% African Americans • 70% Australian Aborigines • 70% Mediterranean and Middle Eastern people • 60% Inuit • 50% Hispanics • 20% Caucasians • 70 years) Women: 1000 mg/day (19–50 years) 1300 mg/day (>50 years)

Upper Level of Intake

Adults: 2500 mg/day

Chief functions in the body

Mineralisation of bones and teeth; also involved in muscle contraction and relaxation, nerve functioning, blood clotting, blood pressure

Deficiency symptoms

Stunted growth in children; bone loss (osteoporosis) in adults

Toxicity symptoms

Constipation; increased risk of urinary stone formation and kidney dysfunction; interference with absorption of other minerals

Significant sources

Dairy products, canned fish with bones, calcium-set tofu, calcium-fortified soy milk, leafy green vegetables (bok choy, broccoli, silverbeet, kale), legumes, almonds, sesame seeds

12.7 Phosphorus

Phosphorus is the second most abundant mineral in the body. About 85 per cent of it is found combined with calcium in the hydroxyapatite crystals of bones and teeth.

Chapter 12: Water and the major minerals

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Phosphorus roles in the body Phosphorus is found not only in bones and teeth, but also in all body cells as part of a major buffer system. Phosphorus is also part of DNA and RNA and is therefore necessary for all growth. Phosphorus assists in energy metabolism. The high-energy compound ATP uses three phosphate groups to do its work. Many enzymes and the B vitamins become active only when a phosphate group is attached. Phospholipids provide stability to the lipoprotein vehicles that help transport other lipids in the blood. Phospholipids are also the major structural components of cell membranes, where they control the transport of nutrients into and out of the cells. Some proteins, such as the casein in milk, contain phosphorus as part of their structures (phosphoproteins).

Phosphorus recommendations and food sources Because phosphorus is commonly found in almost all foods, dietary deficiencies are unlikely. As Figure 12.18 shows, foods rich in proteins, such as meat, poultry, fish, milk, and legumes, are the best sources of phosphorus.

FIGURE 12.18   Phosphorus in selected foods See the ‘How to’ box in Section 10.2, Chapter 10 for more information on using this figure. Milligrams Food

Serving size (kilojoules)

Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg Excellent sources: Liver Almonds Chocolate bar

30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ) 85 g (773 kJ) 30 g (693 kJ) 60 g (1168 kJ)

0

200

400

600

800

1000

RDI for adults

PHOSPHORUS Protein-rich sources, such as milk (white), meats (brown) and legumes (dark blue), provide abundant phosphorus.

Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Miscellaneous Best sources per kilojoule

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Understanding Nutrition

In the past, researchers emphasised the importance of an ideal calcium-to-phosphorus ratio from the diet to support calcium metabolism, but there is little or no evidence to support this concept. The quantities of calcium and phosphorus in the diet are far more important than their ratio to each other. A high phosphorus intake has been blamed for bone loss when, in fact, a low calcium intake – not a phosphorus toxicity or an improper ratio – is responsible. The displacement of milk in the diet by soft drinks, not the phosphoric acid content of the beverages, is the likely culprit for an adverse effect on bones. Phosphate toxicity is rare and usually reflects a significant problem, such as kidney failure.

Refeeding syndrome Refeeding syndrome is a potentially fatal condition that results from a rapid shift in fluids and electrolytes that can occur in people who have undergone several days of starvation and are malnourished. Upon eating again, especially if the foods are high in carbohydrates, there is a rapid spike in insulin, which triggers rapid glucose and electrolyte uptake into the cells, causing a risk of electrolyte deficiencies, particularly phosphorus. Muscle pain, respiratory muscle weakness and cardiac arrhythmias from low blood phosphorus (which is needed for ATP production and cellular oxygen release) and a risk of Wernicke’s encephalopathy due to decreased thiamin stores are all potential consequences. Awareness of the risk of refeeding syndrome, combined with the slow reintroduction of food, replacement of thiamin and monitoring of blood electrolytes are the cornerstones of managing this condition.

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Phosphorus accompanies calcium both in the crystals of bone and in many foods, such as milk. Phosphorus is also important in energy metabolism, as part of phospholipids and as part of the genetic materials DNA and RNA. The summary table below provides a review of phosphorus. PHOSPHORUS Recommended Dietary Intake

Adults: 1000 mg/day

Upper Level of Intake

Adults (19–70 years): 4000 mg/day

Chief functions in the body

Mineralisation of bones and teeth; part of every cell; important in genetic material, part of phospholipids, used in energy transfer and in buffer systems that maintain acid– base balance

Deficiency symptoms

Muscular weakness, bone paina

Toxicity symptoms

Calcification of non-skeletal tissues, particularly the kidneys

Significant sources

Protein-rich foods (meat, fish, poultry, eggs, milk, legumes, nuts)

Dietary deficiency rarely occurs, but some drugs can bind with phosphorus, making it unavailable and resulting in bone loss that is characterised by weakness and pain. a

12.8 Magnesium

Only about 30 grams of magnesium is present in the body. More than half of the body’s magnesium is in the bones. Much of the rest is in the muscles and soft tissues, with only 1 per cent in the extracellular fluid. As with calcium, bone magnesium may serve as a reservoir to ensure normal blood concentrations.

Chapter 12: Water and the major minerals

Magnesium roles in the body In addition to maintaining bone health, magnesium acts in all the cells of the soft tissues, where it forms part of the protein-making machinery and is necessary for energy metabolism. It participates in hundreds of enzyme systems. A major role of magnesium is as a catalyst in the reaction that adds the last phosphate to the high-energy compound ATP, making it essential to the body’s use of glucose; the synthesis of protein, fat and nucleic acids; and the cells’ membrane transport systems. Together with calcium, magnesium is involved in muscle contraction and blood clotting – calcium promotes the processes, whereas magnesium inhibits them. This dynamic interaction between the two minerals helps regulate blood pressure and lung function. Like many other nutrients, magnesium supports the normal functioning of the immune system.

Magnesium food sources

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Reminder: A catalyst is a compound that facilitates chemical reactions without itself being changed in the process. PUTTING COMMON SENSE TO THE TEST

Magnesium mostly serves as an electrolyte. FALSE

The dark blue bars in Figure 12.19 indicate that legumes, seeds and nuts make significant magnesium contributions. Magnesium is part of the chlorophyll molecule, so leafy green vegetables are also good sources. In areas with hard water, the water contributes both calcium and magnesium to daily intakes. The mineral waters noted earlier for their calcium content

FIGURE 12.19   Magnesium in selected foods See the ‘How to’ box in Section 10.2, Chapter 10 for more information on using this figure. Milligrams Food

Serving size (kilojoules)

Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg

30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)

Excellent sources: Halibut Cashews Artichoke

85 g baked (836 kJ) 30 g (676 kJ) 1 (252 kJ)

0

50

100

150

200

250

300

350

400

RDI for men 19–30 MAGNESIUM Legumes (dark blue) are a rich source of magnesium. Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule

RDI for women 19–30

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Understanding Nutrition

may also be magnesium-rich and can be important sources of this mineral for those who drink them. The bioavailability of magnesium from mineral water is about 50 per cent, but it improves when the water is consumed with a meal.

Magnesium deficiency Even with average magnesium intakes below recommendations, deficiency symptoms rarely appear except with diseases. Average magnesium intakes typically fall below recommendations, which may exacerbate inflammation and contribute to chronic diseases, such as heart disease, stroke, hypertension, diabetes and cancer. A severe magnesium deficiency causes a tetany similar to the calcium tetany described earlier. Magnesium deficiencies also impair central nervous system activity and may be responsible for the hallucinations experienced during alcohol withdrawal.

Magnesium and hypertension Magnesium is critical to heart function and seems to lower the risk of hypertension and heart disease.10 Interestingly, people living in areas with hard water, which contains high concentrations of calcium and magnesium (as opposed to soft water, which is high in sodium), tend to have low rates of heart disease. With magnesium deficiency, the walls of the arteries and capillaries tend to constrict – a possible explanation for the hypertensive effect.

Magnesium toxicity Magnesium toxicity is rare, but it can be fatal. The UL for magnesium applies only to non-food sources, such as supplements or magnesium salts.

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Like calcium and phosphorus, magnesium supports bone mineralisation. Magnesium is also involved in numerous enzyme systems and in heart function. It is found abundantly in legumes and leafy green vegetables and, in some areas, in water. The table below offers a summary. MAGNESIUM Recommended Dietary Intake

Men (19–30 years): 400 mg/day Women (19–30 years): 310 mg/day

Upper Level of Intake

Adults: 350 mg non-food magnesium/day

Chief functions in the body

Bone mineralisation; participates in energy metabolism and muscle contraction

Deficiency symptoms

Muscle cramps, tetany, seizures

Toxicity symptoms

From non-food sources only; diarrhoea, nausea, abdominal cramps, metabolic alkalosis

Significant sources

Nuts, legumes, dark-green leafy vegetables, some fish

12.9 Sulphate

Sulphate is the oxidised form of the mineral sulphur, as it exists in food and water. The body’s need for sulphate is easily met by a variety of foods and beverages. In addition, the body receives sulphate from the amino acids methionine and cysteine, which are found in dietary proteins. These sulphur-containing amino acids help determine the contour of protein molecules. The sulphur-containing side chains in cysteine molecules can link to each other, forming disulphide bridges, which stabilise the protein structure. (See the drawing of insulin

Chapter 12: Water and the major minerals

with its disulphide bridges in Figure 6.4 in Section 6.1, Chapter 6.) Skin, hair and nails contain some of the body’s more rigid proteins, which have a high sulphur content. Because the body’s sulphate needs are easily met with normal protein intakes, there is no recommended intake for sulphate. Deficiencies do not occur when diets contain protein. Only when people lack protein to the point of severe deficiency will they lack the sulphurcontaining amino acids.

The Major Minerals CHIEF FUNCTIONS

DEFICIENCY SYMPTOMS

TOXICITY SYMPTOMS

SIGNIFICANT SOURCES

Headache, confusion, stupor, seizures, and coma Not from inadequate intakes but from excessive losses (hyponatraemia)

No evidence of toxicity separate from chronic disease risk

Table salt, soy sauce; ultraprocessed foods

Do not occur under normal circumstances

Vomiting

Table salt, soy sauce; ultraprocessed foods

Irregular heartbeat, muscular weakness, glucose intolerance

Muscular weakness; vomiting; if injected into a vein, can stop the heart

All whole foods; meats, milks, fruits, vegetables, grains, legumes

Stunted growth in children; bone loss (osteoporosis) in adults

Constipation; increased risk of urinary stone formation and kidney dysfunction; interference with absorption of other minerals

Dairy products, canned fish with bones, calciumfortified soy milk, tofu, greens (bok choy, broccoli, silver beet), legumes

Sodium Maintains normal fluid and electrolyte balance; assists in nerve impulse transmission and muscle contraction

Chloride Maintains normal fluid and electrolyte balance; part of hydrochloric acid found in the stomach, necessary for proper digestion Potassium Maintains normal fluid and electrolyte balance; facilitates many reactions; supports cell integrity; assists in nerve impulse transmission and muscle contractions Calcium Mineralisation of bones and teeth; also involved in muscle contraction and relaxation, nerve functioning, blood clotting and blood pressure

REVIEW IT

Like the other nutrients, the action of minerals are coordinated to get the body’s work done. The major minerals, especially sodium, chloride and potassium, influence the body’s fluid balance; whenever an anion moves, a cation moves – always maintaining homeostasis. Sodium, chloride, potassium, calcium and magnesium are key members of the team of nutrients that directs nerve impulse transmission and muscle contraction. They are also the primary nutrients involved in regulating blood pressure. Phosphorus and magnesium participate in many reactions involving glucose, fatty acids, amino acids and the vitamins. Calcium, phosphorus and magnesium combine to form the structure of the bones and teeth. Each major mineral also plays other specific roles in the body. The accompanying table provides a review of facts about the major minerals.

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CHIEF FUNCTIONS

DEFICIENCY SYMPTOMS

TOXICITY SYMPTOMS

SIGNIFICANT SOURCES

Muscular weakness, bone pain

Calcification of nonskeletal tissues, particularly the kidneys

Protein-rich foods (meat, fish, poultry, eggs, milk, legumes, nuts)

Muscle cramps, tetany, seizures

From non-food sources only; diarrhoea, nausea, abdominal cramps; metabolic alkalosis

Nuts, legumes, dark-green leafy vegetables, some fish

None known; protein deficiency would occur first

None reported

Protein-rich foods (meat, fish, poultry, eggs, milk, legumes, nuts)

Phosphorus Mineralisation of bones and teeth; part of every cell; important in genetic material, part of phospholipids, used in energy transfer and in buffer systems that maintain acid–base balance Magnesium Bone mineralisation; participates in energy metabolism and muscle contraction Sulphate As part of proteins, stabilises their shape by forming disulphide bridges; part of the vitamins biotin and thiamin and the hormone insulin

With all of the tasks these minerals perform, they are of great importance to life. Fortunately, consuming enough of each of them every day is easy given a variety of foods from each of the food groups. Wholegrain breads supply magnesium; fruits, vegetables and legumes provide magnesium and potassium; milks offer calcium and phosphorus; meats offer phosphorus and sulphate; all foods provide sodium and chloride, with excesses being more problematic than inadequacies. The message is quite simple and has been repeated throughout this text – for an adequate intake of all the nutrients, including the major minerals, choose different foods from each of the five food groups. And drink plenty of water.

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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 You need eight glasses of water a day to stay hydrated. FALSE

3 Most of the body’s calcium is found in the bones. TRUE



4 The calcium in milk is poorly absorbed. FALSE

Because water requirements are so variable, there is no one set figure that would ensure everyone would be well hydrated. Body size, climate and physical activity levels, and what foods high in water content are eaten dictate how much additional water a person needs to drink.

2 Most of the salt we eat is added to food in its production, not at the table. TRUE

Foods such as bread, processed meat, breakfast cereals and cheese are the main contributors to a person’s salt intake.



Bones contain 99 per cent of the body’s calcium. Around 30 per cent of the calcium in milk is absorbed by the body. While the calcium in some green leafy vegetables can be absorbed at higher rates of 50 per cent, the high amount of calcium found in milks still makes it an excellent dietary source.

5 Magnesium mostly serves as an electrolyte. FALSE

Magnesium is involved in bone health, energy metabolism, muscle contraction and blood clotting.

NUTRITION PORTFOLIO Many people may miss the mark when it comes to drinking enough water to keep their bodies well hydrated or obtaining enough calcium to promote strong bones; in contrast, sodium intakes often exceed those recommended for health. • Describe your strategy for ensuring that you drink plenty of water each day and how you would know if you were sufficiently hydrated.

• •

Explain the importance of selecting and preparing foods with less salt. Estimate how much calcium you consume each day. If you do consume dairy products, what percentage of calcium comes from this source in your diet?

STUDY QUESTIONS Multiple choice questions

c d

Answers can be found at the back of the book. 1

The body generates water during the: a b c d

2

Regulation of fluid and electrolyte balance and acidbase balance depends primarily on the: a b c d

3

kidneys intestines sweat glands specialised tear ducts

ability of their ions to form salts amounts of their contents in the body importance of their functions in the body capacity to retain their identity after absorption.

The principal cation in extracellular fluids is: a b

sodium chloride

An important role of chloride is to: a b c d

6

7

Broccoli Eggs Cornflakes Whole-wheat bread.

Calcium homeostasis depends on: a b c d

8

metabolise folate inhibit the absorption of vitamin B12 produce stomach acid assist in the production of aldosterone.

Which food would provide the most potassium? a b c d

The distinction between the major and trace minerals reflects the: a b c d

4

5

buffering of acids dismantling of bone metabolism of minerals breakdown of energy nutrients.

potassium phosphorus.

vitamin K, aldosterone and renin vitamin K, parathyroid hormone and renin vitamin D, aldosterone and calcitonin vitamin D, calcitonin and parathyroid hormone.

Calcium absorption is improved by: a b c d

oxalates vitamin D low stomach acid phytates in nuts and seeds.

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Phosphorus assists in many activities in the body, but not: a b c d

10 Most of the body’s magnesium can be found in the: a b c d

energy metabolism the clotting of blood the transport of lipids bone and teeth formation.

bones nerves muscles extracellular fluid.

REVIEW QUESTIONS 1

List the roles of water in the body. (Section 12.1)

8

List calcium’s roles in the body. (Section 12.6)

2

What is ADH? Where does it exert its action? What is aldosterone? How does it work? (Section 12.1)

9

3

How do the concentrations of the main electrolytes differ between the intracellular and extracellular compartments? (Section 12.1)

How does the body keep blood calcium constant regardless of intake, and what are the roles of vitamin D and parathyroid hormone in the process? (Section 12.6)

4

List the sources of water intake and routes of water excretion. (Section 12.1)

5

What do the terms ‘major’ and ‘trace’ mean when describing the minerals in the body? (Section 12.2)

6

Describe some characteristics of minerals that distinguish them from vitamins. (Section 12.2)

7

What is the major function of sodium in the body? Describe how the kidneys regulate blood sodium. Is a dietary deficiency of sodium likely? Why or why not? (Section 12.3)

10 Name significant food sources of calcium. What are the consequences of inadequate intakes? (Section 12.6) 11 List the roles of phosphorus in the body. Discuss the relationships between calcium and phosphorus. Is a dietary deficiency of phosphorus likely? Why or why not? (Section 12.7) 12 State the major functions of chloride, potassium, magnesium and sulphur in the body. Are deficiencies of these nutrients likely to occur in your own diet? Why or why not? (Sections 12.4, 12.5, 12.8, 12.9)

NUTRITION CALCULATIONS These problems give you an appreciation for the minerals in foods. Be sure to show your calculations (answers can be found in the Answers section at the back of this book).

FOOD

CALCIUM IN THE FOOD (mg)

ABSORPTION RATE (%)

CALCIUM IN THE BODY (mg)

1

Cauliflower, ½ cup cooked, fresh

10

≥50

≥5

Broccoli, ½ cup cooked, fresh

36

Milk, 1 cup full-fat

300

Almonds, 30 g

75

Spinach, 1 cup, raw

55

For each of these minerals, note the unit of measure: a b c d e

calcium magnesium phosphorus potassium sodium.

2 a Consider how the rate of absorption influences the amount of calcium available for the body’s use. Use Figure 12.16 in Section 12.6 to determine how much calcium the body actually receives from the foods listed in the accompanying table by multiplying the milligrams of calcium in the food by the percentage absorbed. The first one is done for you.

b

To appreciate how the absorption rate influences the amount of calcium available to the body, compare broccoli with almonds. Which provides more calcium in foods and to the body?

Chapter 12: Water and the major minerals

c

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an equivalent amount of calcium as from 1 cup of milk? How does your answer change when you account for differences in their absorption rates?

To appreciate how the calcium content of foods influences the amount of calcium available to the body, compare cauliflower with milk. How much cauliflower would a person have to eat to receive

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search ‘minerals’ at the Dietitians Australia site: http://www.dietitiansaustralia.org.au • Learn about sodium in foods and on food labels by searching ‘salt’ or ‘sodium’ at the Food Standards

•

•

Australia New Zealand website: http://www. foodstandards.gov.au Learn why Australians should reduce how much salt they are eating at the website of the Australian Division of World Action on Salt & Health: http://www.awash. org.au Learn about the benefits of calcium from Healthy Bones Australia: http://www.healthybonesaustralia. org.au

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HIGHLIGHT

12

12.10 OSTEOPOROSIS AND CALCIUM

Shutterstock.com/Makistock

Osteoporosis becomes apparent during the later years, but it develops much earlier – and without warning. Osteoporosis is rightly called a disease of older age that originates in youth. Few people are aware that their bones are being robbed of their strength. The problem often first becomes evident when someone’s hip suddenly gives way. People say, ‘She fell and broke her hip’, but in fact the hip may have been so fragile that it broke before she fell. Even bumping into a table may be enough to shatter a porous bone into fragments so numerous and scattered that they cannot be reassembled. Removing them and replacing them with an artificial joint requires major surgery. Of those suffering a hip fracture, many will die from complications within a year while others will never walk or live independently again. Their quality of life slips downward.

Obtaining plenty of calcium from the diet is important in maintaining healthy bones.

This highlight examines osteoporosis, one of the most prevalent diseases of ageing. An estimated 924 000 Australians have osteoporosis while 20 per cent of people aged 75 years and over have osteoporosis.1 In New Zealand, one in three women and one in five men will suffer from an osteoporotic fracture during their lifetime.2 This highlight reviews the many factors that contribute to a new hospitalisation every few minutes from breaks in

the bones of the hips, vertebrae, wrists, arms and ankles. And it presents strategies to reduce the risks, paying special attention to the role of dietary calcium.

Bone development and disintegration Bone has two compartments: the outer, hard shell of cortical bone and the inner, lacy matrix of trabecular bone. Both can lose minerals, but in different ways and at different rates. The left-hand photograph in Figure H12.1 shows a human leg bone sliced lengthwise, exposing the lacy, calcium-containing crystals of trabecular bone. These crystals give up calcium to the blood when the diet runs short, and they take up calcium again when the supply is plentiful (review Figure 12.14 in Section 12.6). For people who have eaten calcium-rich foods throughout the boneforming years of their youth, these deposits make bones dense and provide a rich reservoir of calcium. A close look at the first photograph in Figure H12.1 also reveals that a dense, ivory-like exterior shell, the cortical bone, protects the interior trabecular bone. Cortical bone composes the shafts of the long bones, and a thin cortical shell caps the end of the bone. Both compartments confer strength on bone – cortical bone provides the sturdy outer wall, and trabecular bone provides support along the lines of stress. The two types of bone play different roles in calcium balance and osteoporosis. Supplied with blood vessels and metabolically active, trabecular bone is sensitive to hormones that govern day-to-day deposits and withdrawals of calcium. It readily gives up minerals whenever blood calcium needs replenishing. Losses of trabecular bone start becoming significant for men and women in their thirties, although losses can occur whenever calcium withdrawals exceed deposits. Cortical bone also gives up calcium, but slowly and at a steady pace. Cortical bone losses typically begin at about age 40 and continue slowly but surely thereafter. As bone loss continues, bone density declines, and osteoporosis becomes apparent (see Figure H12.1). Bones become so fragile that even the body’s own weight can overburden the spine – vertebrae may suddenly disintegrate and crush down, painfully pinching major nerves. Or the vertebrae may compress into wedge shapes,

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Trabecular bone is lacy the network lacy network Trabecular bone is the of calcium-containing crystalscrystals that fills that the of calcium-containing interior. bone is the dense, fills theCortical interior. Cortical bone is ivorylike bone that forms the exterior the dense, ivory-like bone that shell.

Electron micrograph of healthy Electron micrograph of healthy trabecular bone trabecular bone

© Permission by David Dempster from J. Bone Miner Res, 1986

Courtesy of Gjon Mili

© Permission by David Dempster from J. Bone Miner Res, 1986

FIGURE H12.1   Healthy and osteoporotic trabecular bones

Electron micrograph of trabecular Electron micrograph of trabecular bone bone by osteoporosis affectedaffected by osteoporosis

forms the exterior shell.

forming what is often called a ‘dowager’s hump’, the posture many older people assume as they ‘grow shorter’. Figure H12.2 shows the effect of compressed spinal bone on a woman’s height and posture. Because both the cortical shell and the trabecular interior weaken, breaks most often occur in the hip. Physicians can diagnose osteoporosis and assess the risk of bone fractures by measuring bone density using dual-energy X-ray absorptiometry (DEXA scan) or ultrasound. They also consider risk factors that predict bone fractures, including age, personal and family history of fracture, BMI and physical inactivity. Table H12.1 summarises the major risk factors for osteoporosis. The more risk factors that apply to a person, the greater the chances of bone loss. Notice that several risk factors that are influential in the development of osteoporosis, such as age, sex and genetics, cannot be changed. Other risk factors, such as diet, physical activity, body weight, smoking and alcohol use, are personal behaviours that can be changed. By eating a calcium-rich and vitamin D rich, well-balanced diet; being physically active; abstaining from smoking; and drinking alcohol in moderation (if at all), people can defend themselves against osteoporosis.3 These decisions are particularly important for those with other risk factors that cannot be changed. Whether a person develops osteoporosis seems to depend on the interactions of several factors, including nutrition. The strongest predictor of bone density is age.

Age and bone calcium Two major stages of life are critical in the development of osteoporosis. The first is the bone-acquiring stage of childhood and adolescence. The second is the bonelosing decades of late adulthood, especially in women after menopause. The bones gain strength and density all through the growing years and into young adulthood. As people age, the cells that build bone gradually become less active, but those that dismantle bone continue working. The result is that bone loss exceeds bone formation. Some bone loss is inevitable, but losses can be curtailed by maximising bone mass.

Maximising bone mass To maximise bone mass, the diet must deliver an adequate supply of calcium during the first three decades of life. Children and teens who get enough calcium and vitamin D have denser bones than those with inadequate intakes. With little or no calcium from the diet, the body must depend on bone to supply calcium to the blood – bone mass diminishes, and bones lose their density and strength. When people reach the bone-losing years of middle age, those who formed dense bones during their youth have the advantage. They simply have more bone starting out and can lose more before suffering ill effects. Figure H12.3 demonstrates this effect.

Understanding Nutrition

FIGURE H12.2   Loss of height in a woman caused by osteoporosis The woman on the left is about 50 years old. The woman on the right is 80 years old. Her legs have not grown shorter. Instead, her back has lost length due to collapse of her spinal bones (vertebrae). Collapsed vertebrae cannot protect the spinal nerves from pressure that causes excruciating pain.

© Permission by David Dempster from J. Bone Miner Res, 1986

15 centimetres lost

50 years old

80 years old

Minimising bone loss Not only does dietary calcium build strong bones in youth, it remains important in protecting against losses in the later years. Unfortunately, calcium intakes of older adults are typically low, and calcium absorption declines after menopause. The kidneys do not activate vitamin D as well as they did earlier (recall that active vitamin D enhances calcium absorption). Also, sunlight is needed to form vitamin D, and many older people spend little or no time outdoors in the sunshine. For these reasons, and because

TABLE H12.1   Risk factors for osteoporosis NON-MODIFIABLE

MODIFIABLE

Female

Sedentary lifestyle

Older age (>50 yrs)

Diet inadequate in calcium and vitamin D

Small frame

Diet excessive in protein, sodium and caffeine

Caucasian, Asian or Hispanic heritage

Cigarette smoking

Family history of osteoporosis or fractures

Alcohol abuse

Personal history of fractures

Low body weight

Oestrogen deficiency in women (amenorrhea or menopause, especially early or surgically induced); testosterone deficiency in men

Certain medications, such as glucocorticoids, aluminium-containing antacids, and antiseizure drugs

Science Photo Library/Doncaster and Bassetlaw Hospitals

434

Using a DEXA (dual-energy X-ray absorptiometry) scan to measure bone mineral density identifies osteoporosis, determines risks for fractures and tracks responses to treatment.

intakes of vitamin D are typically low anyway, blood vitamin D declines. Some of the hormones that influence bone and calcium metabolism – parathyroid hormone, calcitonin, oestrogen and testosterone – also change with age, and

Chapter 12: Water and the major minerals

FIGURE H12.3   Bone losses over time compared Peak bone mass is achieved by age 30. Women gradually lose bone mass until menopause when losses accelerate dramatically and then gradually taper off.

Bone mass

Woman A entered adulthood with enough calcium in her bones to last a lifetime.

Osteopenia

Woman B had less bone mass starting out, and so suffered ill effects from bone loss later on.

Osteoporosis Age 30

Menopause

Age 60

Time

Note: People with a moderate degree of bone mass reduction are said to have osteopenia and are at increased risk of fractures. Data from Committee on Dietary Reference Intakes, Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride, Washington, DC: National Academy Press (1997): 71−145.

these changes accelerate bone loss. Together, these agerelated factors contribute to bone loss: inefficient bone remodelling, reduced calcium intakes, impaired calcium absorption, poor vitamin D status, and hormonal changes that favour bone mineral withdrawal.

Sex and hormones After age, sex is the next strongest predictor of osteoporosis. The sex hormones play a major role in regulating the rate of bone turnover. In general, men have greater bone density than women at maturity, and women suffer greater losses than men in later life. Consequently, men develop bone problems five to 10 years later than women, and women have a four times higher rate of osteoporosis.4 Menopause imperils women’s bones. Bone dwindles rapidly when the hormone oestrogen diminishes and menstruation ceases. The lack of oestrogen contributes to the release of cytokines that produce inflammation and accelerate bone loss. Women may lose up to 20 per cent of their bone mass during the six to eight years following the onset of menopause. Eventually, losses taper off so that women again lose bone at the same rate as men their age. Losses of bone minerals continue throughout the remainder of a woman’s lifetime, but not at the free-fall pace of the menopause years (review Figure H12.3).

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Rapid bone losses also occur when young women’s ovaries fail to produce enough oestrogen, causing menstruation to cease. In some cases, diseased ovaries are to blame and must be removed; in others, the ovaries fail to produce sufficient oestrogen because the women suffer from anorexia nervosa and have unreasonably restricted their body weight (see Highlight 8). Amenorrhoea and low body weights explain much of the bone loss seen in these young women, even years after diagnosis and treatment. Oestrogen therapy can help non-menstruating women prevent further bone loss and reduce the incidence of fractures. Because oestrogen therapy may increase the risks for breast cancer, women must carefully weigh any potential benefits against the possible dangers. Several drug therapies have been developed to inhibit bone loss and enhance bone formation. A combination of drugs or of hormone replacement and a drug may be most beneficial. Some women who choose not to use oestrogen therapy turn to soy as an alternative treatment. Interestingly, the phytochemicals commonly found in soy mimic the actions of oestrogen in the body. Research results have been mixed and controversial, but overall seem to indicate a lack of benefit for soy and its phytochemicals in helping to prevent the rapid bone losses of the menopause years.5 If oestrogen deficiency is a major cause of osteoporosis in women, what is the cause of bone loss in men? The male sex hormone testosterone appears to play a role. Men with low levels of testosterone, as occurs after removal of diseased testes or when testes lose function with ageing, suffer more fractures. Treatment for men with osteoporosis includes testosterone replacement therapy. Thus, both male and female sex hormones participate in the development and treatment of osteoporosis.

Genetics The role of genetics in osteoporosis is strong, although still unclear.6 Most likely, genes influence both the peak bone mass achieved during growth and the bone loss incurred during the later years. The extent to which a given genetic potential is realised, however, depends on many outside factors. Diet and physical activity, for example, can maximise peak bone density during growth, whereas alcohol and tobacco abuse can accelerate bone losses later in life. It is noteworthy that these factors are within a person’s control.

Physical activity and body weight Physical activity may be the single most important factor supporting bone growth during adolescence. Active adolescents have denser bones, which provides protection against fractures in adulthood.7 Muscle strength and bone

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Smoking and alcohol Add bone damage to the list of ill consequences associated with smoking. The bones of smokers are less dense than those of non-smokers – even after controlling for differences in age, body weight and physical activity habits. Fortunately, the damaging effects can be reversed with smoking cessation. Blood indicators of beneficial bone activity are apparent six weeks after a person stops smoking. In time, the bone density of former smokers is similar to that of non-smokers. People who abuse alcohol often suffer from osteoporosis and experience more bone breaks than others. Several factors appear to be involved. Alcohol enhances fluid excretion, leading to excessive calcium losses in the urine; upsets the hormonal balance required for healthy bones; slows bone formation, leading to lower bone density; stimulates bone breakdown; and increases the risk of falling.

Shutterstock.com/Catalin Petolea

Dietary calcium

High-impact exercises, such as jumping rope, are most consistently effective in building bone density. Other weight-bearing activities, such as resistance training, specific yoga postures, and walking also support strong bones.

strength go together. When muscles work, they pull on the bones, stimulating them to develop more trabeculae and grow denser. The hormones that promote new muscle growth also favour the building of bone. As a result, active bones are denser and stronger than sedentary bones. Both the muscle contraction and the gravitational pull of the body’s weight create a load that benefits bone metabolism. To keep bones healthy, a person should engage in weight training or weightbearing activities at least twice a week. Heavier body weights and weight gains place similar stresses on the bones and increase their density. In contrast, weight losses reduce bone density and increase the risk of fractures – in part because energy restriction diminishes calcium absorption and compromises calcium balance. As Highlight 8 mentions, the relative energy deficiency that results from a combination of restricted energy intake and extreme daily exercise reliably predicts bone loss.

Bone strength later in life depends most on how well the bones were built during childhood and adolescence. Adequate calcium nutrition during the growing years is essential to achieving optimal peak bone mass. To that end, the NRVs for Australia and New Zealand recommend 1300 milligrams of calcium per day for everyone from 12 to 18 years of age. Unfortunately, few girls meet the recommendations for calcium during these bone-forming years. (Boys generally obtain intakes close to those recommended because they eat more food.) Consequently, most girls start their adult years with less-than-optimal bone density. As adults, women under the age of 50 rarely meet their recommended intakes of 1000 milligrams from food.

Other nutrients Much research has focused on calcium, but other nutrients support bone health, too. Adequate protein protects bones and reduces the likelihood of hip fractures. As mentioned earlier, vitamin D is needed to maintain calcium metabolism and optimal bone health. Vitamin K regulates bone and cartilage mineralisation and decreases bone turnover.8 Vitamin C may slow bone losses. The minerals magnesium and potassium also help maintain bone mineral density. Vitamin A is needed in the boneremodelling process, but too much vitamin A may be associated with osteoporosis. Carotenoids may inhibit bone loss. Omega-3 fatty acids may help preserve bone integrity. Additional research points to the bone benefits not of a specific nutrient, but of a diet rich in fruits, vegetables and whole grains. In contrast, diets containing too much salt are associated with bone losses. Similarly,

Chapter 12: Water and the major minerals

diets containing too many soft drinks or commercially baked snack and fried foods are associated with low bone mineral density. Clearly, a well-balanced diet that depends on all the food groups to supply a full array of nutrients is central to bone health.

A perspective on calcium supplements This highlight has emphasised that bone health depends largely on calcium and has suggested many foods as good calcium sources but has not endorsed the taking of calcium supplements. A person who finds it difficult or impossible to consume even half of the recommended calcium intake from milk and other calcium-rich foods should try one more strategy – consult a dietitian who can assess their diet and suggest food choices to correct any inadequacies. Calcium from foods may support bone health better than calcium from supplements. For those who are unable to consume enough calcium-rich foods, however, taking calcium supplements – especially in combination with vitamin D – may help enhance bone density and protect against bone loss and fractures. Because some research suggests that calcium from supplements may increase the risk of heart attacks and strokes, women should consult their physicians when making this decision.9 Selecting a calcium supplement requires a little investigative work to sort through the many options. Before comparing calcium supplements, recognise that multivitamin-mineral pills contain little or no calcium. The label may list a few milligrams of calcium but remember that the recommended intake is a gram (1000 mg) or more for adults. Calcium supplements are typically sold as compounds of calcium carbonate (common in antacids), citrate, gluconate, lactate, malate or phosphate. These supplements often include magnesium, vitamin D or both. In addition, some calcium supplements are made from bone meal (or powdered bone), oyster shell or dolomite (limestone). Many calcium supplements, especially those derived from these natural products, contain lead – which impairs health in numerous ways, as Chapter 13 points out. Fortunately, calcium interferes with the absorption and action of lead in the body. The first question to ask is how much calcium the supplement provides. Most calcium supplements provide between 250 and 1000 milligrams of calcium. To be safe, total calcium intake from both foods and supplements should not exceed 2500 milligrams a day. Read the label to find out how much a dose supplies. Unless the label states otherwise, supplements of calcium carbonate are 40 per cent calcium; those of calcium citrate are 21 per cent; lactate, 13 per cent; and gluconate, 9 per cent. Select a low-dose supplement and

437

take it several times a day, rather than taking a large-dose supplement all at once. Taking supplements in doses of 500 milligrams or less improves absorption better than taking larger doses less frequently. Small doses also help ease the GI distress (constipation, intestinal bloating and excessive gas) that sometimes accompanies calcium supplement use. Supplements containing calcium carbonate require stomach acidity for optimal absorption and so are best taken with meals. People who suffer from reduced gastric acid production or are taking medications that inhibit gastric acid secretion are advised to take calcium citrate supplements rather than calcium carbonate. The next question to ask is how well the body absorbs and uses the calcium from various supplements. Most healthy people absorb calcium equally well from milk and from the supplements calcium carbonate, citrate and phosphate. More important than supplement solubility is tablet disintegration. When manufacturers compress large quantities of calcium into small pills, the stomach acid has difficulty penetrating the pill. To test a supplement’s ability to dissolve, drop it into a cup of vinegar and stir occasionally. A high-quality formulation will dissolve within a half hour. Finally, people who choose supplements must take them regularly. Furthermore, consideration should be given to the best time to take the supplements. To circumvent adverse nutrient interactions, take calcium supplements between, not with, meals. (Importantly, do not take calcium supplements with iron supplements or iron-rich meals because calcium inhibits iron absorption.) To enhance calcium absorption, take supplements with meals. If such contradictory advice annoys you, reconsider the benefits of food sources of calcium. Most experts agree that foods are the best source of most nutrients, and especially of calcium.

Some closing thoughts Unfortunately, many of the strongest risk factors for osteoporosis are beyond people’s control: age, sex and genetics. But several strategies are still effective for prevention. First, ensure an optimal peak bone mass during childhood and adolescence by eating a balanced diet rich in calcium and vitamin D and engaging in regular physical activity. Then maintain that bone mass by continuing those healthy diet and activity habits, abstaining from cigarette smoking and using alcohol only moderately, if at all. Finally, minimise bone loss by maintaining an adequate nutrition and exercise regimen, and, for women, consult a doctor about calcium supplements or other drug therapies that may be effective both in preventing bone loss and in restoring lost bone. The reward is the best possible chance of preserving bone health throughout life.

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Understanding Nutrition

HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1

Examine your own lifestyle behaviours and evaluate which ones are most likely to be protective against developing osteoporosis. Which ones do you believe that you have the most realistic chance of changing?

2

Osteoporosis typically develops in old age, yet the time to optimise bone density is during childhood

and adolescence – decades away from the realities of hip fractures and spinal collapses. What plan of action might you develop to encourage teens to adopt strategies that will enhance bone development? Be sure to address potential obstacles and reluctance typical of that age.

NUTRITION ON THE NET Find out more information online. • Obtain additional information from Healthy Bones Australia: https://healthybonesaustralia.org.au • Read about practical advice on maintaining healthy bones from the Jean Hailes organisation http:// jeanhailes.org.au

• •

Search for ‘falls and fractures’ at the National Ageing Research Institute: http://www.nari.net.au Visit the National Institutes of Health Osteoporosis and Related Bone Diseases National Resource Center: http://bones.nih.gov

REFERENCES CHAPTER 1

2 3

4

5

Y. Zhang and co-authors, Caffeine and diuresis during rest and exercise: A meta-analysis, Journal of Science and Medicine in Sport 18 (2015): 569–574. A. Grillo and co-authors, Sodium intake and hypertension, Nutrients 11 (2019): 1970. C. Ozemek and co-authors, The role of diet for prevention and management of hypertension, Current Opinion in Cardiology a22 (2018): 388–393. Food Standards Australia New Zealand: How much sodium and salt are we eating? available at http://www.foodstandards.gov.au/ scienceandeducation/factsheets/factsheets/howmuchsaltareweeating/ howmuchsaltandsodium4551.cfm N. R. Cook, L. J. Appel, and P. K. Whelton, Sodium intake and allcause mortality over 20 years in the trials of hypertension prevention, Journal of the American College of Cardiology 68 (2016): 1609–1617.

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8

9

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T. Filippini and co-authors, Potassium intake and blood pressure: A dose-response meta-analysis of randomized controlled trials, Journal of the American Heart Foundation 9 (2020): e015719. E. Z. Movassagh, Vegetarian-style dietary pattern during adolescence has long-term positive impact on bone from adolescence to young adulthood: A longitudinal study. Nutrition Journal 17 (2018): 36. P. Yao, D. Bennett and M. Mafham, Vitamin D and calcium for the prevention of fracture: A systematic review and meta-analysis, JAMA Network Open 2 (2019): e1917789. K. Li and co-authors, The good, the bad, and the ugly of calcium supplementation: A review of calcium intake on human health, Clinical Interventions in Aging 13 (2018): 2443–2452. N. Rosique-Esteban and co-authors, Dietary magnesium and cardiovascular disease: A review with emphasis in epidemiological studies, Nutrients 10 (2018): E168.

HIGHLIGHT 1

2

3 4 5

6

Australian Bureau of Statistics, National health survey: first results, 2017–18, ABS Catalogue Number 4364.0.55.001, Canberra: ABS (2018). Osteoporosis New Zealand, Osteoporosis New Zealand Annual Report 2017, available at https://osteoporosis.org.nz/wp-content/uploads/ ONZ-2017-Annual-Report-WEB.pdf P. A. Anderson and co-authors, Bone health optimization: beyond own the bone, Journal of Bone and Joint Surgery 101 (2019): 1413–1419. K. A. Alswat, Gender disparities in osteoporosis, Journal of Clinical Medical Research 9 (2017): 382–387. I. M. C. M. Rietjens, J. Louisse and K. Beekmann, The potential health effects of dietary phytoestrogens, British Journal of Pharmacology 174 (2017): 1263–1280. L. Zhang and co-authors, Associations between VDR gene polymorphisms and osteoporosis risk and bone mineral density in

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postmenopausal women: A systematic review and meta-analysis, Scientific Reports 8 (2018): 981. K. L. Troy and co-authors, Exercise early and often: Effects of physical activity and exercise on women’s bone health, International Journal of Environmental Research and Public Health 15 (2018): 878. M. Fusaro, Vitamin K and bone, Clinical Cases in Mineral and Bone Metabolism, 14 (2017): 200–206. J. J. B. Anderson and co-authors, Calcium intake from diet and supplements and the risk of coronary artery calcification and its progression among older adults: 10-year follow-up of the MultiEthnic Study of Atherosclerosis (MESA), Journal of the American Heart Association 5 (2016): e003815.

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THE TRACE MINERALS Nutrition in your life

A trace is a barely perceptible amount, but the trace minerals tackle big jobs. Your blood can’t carry oxygen without iron, and insulin can’t deliver glucose without chromium. Teeth decay without fluoride, and thyroid glands develop goitre without sufficient iodine. Together, the trace minerals keep you healthy and strong. Where can you get these amazing minerals? A variety of foods, especially those from the meat and meat alternative group, sprinkled with a little iodised salt and complemented by a glass of fluoridated water will do the trick. It’s remarkable what your body can do with only a few milligrams – or even micrograms – of the trace minerals. As you read this chapter, consider whether the foods you are eating are meeting your trace mineral needs. PUTTING COMMON SENSE TO THE TEST Circle your answer

T F Iron from animal foods is normally absorbed better than iron from plant foods. T F Vegetarians require the same amount of iron in their diet as meat eaters. T F Plant foods are the best sources of zinc in the diet. T F Seafood is a good source of iodine. T F Bottled water is a good source of fluoride.

LEARNING OBJECTIVES 13.1 Summarise key factors unique to the trace minerals. 13.2 Identify the main roles, deficiency symptoms and food sources for iron. 13.3 Identify the main roles, deficiency symptoms and food sources for zinc. 13.4 Identify the main roles, deficiency symptoms and food sources for iodine. 13.5 Identify the main roles, deficiency symptoms and food sources for selenium. 13.6 Identify the main roles, deficiency symptoms and food sources for copper.

13.7 Identify the main roles, deficiency symptoms and food sources for manganese. 13.8 Identify the main roles, deficiency symptoms and food sources for fluoride. 13.9 Identify the main roles, deficiency symptoms and food sources for chromium. 13.10 Identify the main roles, deficiency symptoms and food sources for molybdenum. 13.11 Identify the importance of other trace minerals and describe the health effects of contaminant minerals. 13.12 Define phytochemicals and explain how they might defend against chronic diseases. Tomatoes are a rich source of the vitamin A pigment lycopene, which gives them their rich red colour

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This chapter features the essential trace minerals – iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium and molybdenum. Figure 12.10 (Section 12.2, Chapter 12) shows the tiny quantities of trace minerals in the human body. The trace minerals are so named because they are present, and needed, in relatively small amounts in the body. All together, they would produce only a bit of dust, hardly enough to fill a teaspoon. Yet they are no less important than the major minerals or any of the other nutrients. Each of the trace minerals performs a vital role. A deficiency of any of them may be fatal, and an excess of many is equally deadly. Remarkably, people’s diets normally supply just enough of these minerals to maintain health. This chapter also mentions other trace minerals, such as arsenic, boron, nickel, bromine and vanadium, that are not considered nutrients. These minerals may have beneficial roles in the body, but research on them is insufficient to determine how essential they are. Also mentioned in this chapter are contaminant minerals that disrupt body processes and impair nutrition status. The highlight that follows examines phytochemicals – compounds that also are not essential nutrients but that have biological activity in the body. Again, a well-balanced diet – especially one abundant in fruits and vegetables – supplies a full array of phytochemicals to support good health.

13.1  The trace minerals: an overview

The trace minerals participate in diverse tasks all over the body. Each has special duties that only it can perform. Reminder: Bioavailability refers to the rate at, and the extent to which, a nutrient is absorbed and used.

Trace minerals food sources The trace mineral contents of foods depend on soil and water composition and how foods are processed. Furthermore, many factors in the diet and within the body affect the minerals’ bioavailability. Still, outstanding food sources for each of the trace minerals, just like those for the other nutrients, include a wide variety of foods.

Trace minerals deficiencies Assessing trace mineral status is challenging. Severe deficiencies of the better-known minerals are easy to recognise. Deficiencies of the others may be harder to diagnose, and for all minerals, mild deficiencies are easy to overlook. Because the minerals are active in all the body systems – digestive, cardiovascular, circulatory, muscular, skeletal and nervous – deficiencies can have wide-reaching effects and can affect people of all ages. The most common result of a deficiency in children is failure to grow and thrive.

Trace minerals toxicities Most of the trace minerals are toxic at intakes only two and a half to 11 times above current recommendations. Thus, it is important not to habitually exceed the Upper Level of Intake (UL). Many dietary supplements contain trace minerals, making it easy for users to exceed their needs. Highlight 10 discusses supplement use and some of the regulations around their production and promotion. Individuals who take supplements must therefore be aware of the possible dangers and so select supplements that contain doses that would not mean they exceed the recommended UL. It would be easier and safer to meet nutrient needs by selecting a variety of foods than by combining an assortment of supplements.

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Trace minerals interactions Interactions among the trace minerals are common and often well coordinated to meet the body’s needs. For example, several of the trace minerals support insulin’s work, influencing its synthesis, storage, release and action. At other times, interactions lead to nutrient imbalances. An excess of one may cause a deficiency of another (e.g. a slight manganese overload may aggravate an iron deficiency). A deficiency of one may interfere with the work of another (e.g. a selenium deficiency halts the activation of the iodine-containing thyroid hormones). A deficiency of a trace mineral may even open the way for a contaminant mineral to cause a toxic reaction (e.g. iron deficiency makes the body vulnerable to lead poisoning). These examples of nutrient interactions highlight one of the many reasons why people should use supplements conservatively, if at all – supplementation can easily create imbalances. A good food source of one nutrient may be a poor food source of another, and factors that enhance the action of some trace minerals may interfere with others. Red meat, for example, is a good source of iron but a poor source of calcium; vitamin C enhances the absorption of iron but hinders that of copper. REVIEW IT

Although the body uses only tiny amounts of the trace minerals, they are vital to health. Because so little is required, the trace minerals can be toxic at levels not far above estimated requirements – a consideration for supplement users. Like the other nutrients, the trace minerals are best obtained by eating a variety of whole foods.

13.2 Iron

Iron is an essential nutrient, vital to many of the cells’ activities, but iron deficiencies and excesses pose problems for millions of people. Some people simply don’t eat enough ironcontaining foods to support their health optimally. Others absorb so much iron that it threatens their health. Iron exemplifies the principle that both too little and too much of a nutrient in the body can be harmful. In its efforts to protect against both deficiency and toxicity, the body regulates iron transport and maintains iron balance in several ways.

Iron’s two ionic states: • ferrous iron (reduced): Fe++ • ferric iron (oxidised): Fe+++

Iron roles in the body

Reminder: A cofactor is a substance that works with an enzyme to facilitate a chemical reaction.

Iron has the ability to switch back and forth between two ionic states. In the reduced state, iron has lost two electrons and therefore has a net positive charge of two; it is known as ferrous iron. In the oxidised state, iron has lost a third electron, has a net positive charge of three and is known as ferric iron. Ferrous iron can be oxidised to ferric iron, and ferric iron can be reduced to ferrous iron. Thus, iron can serve as a cofactor to enzymes involved in oxidation–reduction reactions – reactions so widespread in metabolism that they occur in all cells. Enzymes involved in making amino acids, collagen, hormones and neurotransmitters all require iron to be active. (For details about ions, oxidation and reduction, see Appendix B.) Iron forms a part of the electron carriers that participate in the electron transport chain (discussed in Chapter 7). The iron-containing electron carriers of the electron transport chain are known as cytochromes (see Appendix C for details of this pathway). These carriers transfer hydrogens and electrons to oxygen, forming water, and in the process make ATP for the cells’ energy use. Most of the body’s iron is found in two proteins: haemoglobin in the red blood cells and myoglobin in the muscle cells. In both, iron helps accept, carry and then release oxygen.

Reminder: Haemoglobin is the oxygen-carrying protein of the red blood cells that transports oxygen from the lungs to tissues throughout the body; haemoglobin accounts for 80% of the body’s iron.

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FIGURE 13.1   Iron absorption

Iron in food

Mucosal cells in the intestine store excess iron in mucosal ferritin (a storage protein).

If the body does not need iron

Iron is not absorbed and is excreted in shed intestinal cells instead. Thus, iron absorption is reduced when the body does not need iron.

If the body needs iron Mucosal ferritin releases iron to mucosal transferrin (a transport protein), which hands off iron to another transferrin that travels through the blood to the rest of the body.

Iron absorption and metabolism The body conserves iron. Because it is difficult to excrete iron once it is in the body, balance is maintained primarily through absorption. More iron is absorbed when stores are empty and less is absorbed when stores are full. A mucous membrane such as the one that lines the GI tract is sometimes called the mucosa. The adjective of mucosa is mucosal.

PUTTING COMMON SENSE TO THE TEST

Iron from animal foods is normally absorbed better than iron from plant foods. TRUE

Iron absorption

Special proteins help the body absorb iron from food (see Figure 13.1). One protein, called ferritin, receives iron from food and stores it in the mucosal cells of the small intestine. When the body needs iron, ferritin releases some iron to another protein, called transferrin. If the body does not need iron, it is carried out when the intestinal cells are shed and excreted in the faeces; intestinal cells are replaced about every three to five days. By holding iron temporarily, these cells control iron absorption by either delivering iron when the day’s intake falls short or disposing of it when stores are full. This is an important regulatory process to prevent iron toxicity because, apart from blood loss, the body does not have a ready way to excrete excess iron once it has been absorbed.

Haem and non-haem iron Iron absorption depends in part on its dietary source. Iron occurs in two forms in foods: as haem iron, which is found only in foods derived from the flesh of animals, such as meats, poultry and fish, and as non-haem iron, which is found in both plant-derived and animalderived foods (see Figure 13.2). On average, haem iron represents about 10 per cent of the iron a person consumes in a day. Even though haem iron accounts for only a small proportion of the intake, it is so well absorbed that it contributes significant iron. About 25 per cent of haem iron and 17 per cent of non-haem iron is absorbed, depending on dietary factors and the body’s iron stores.1 In iron deficiency, absorption increases. In iron overload, absorption declines.

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FIGURE 13.2   Haem and non-haem iron in foods About 40% of the iron in meat, fish, and poultry is bound into haem; the other 60% is non-haem iron. Key: Haem Non-haem

Haem accounts for about 10% of the average daily iron intake, but it is well absorbed (about 25%). Non-haem iron accounts for the remaining 90%, but it is less well absorbed (about 17%).

All of the iron in foods derived from plants is non-haem iron.

Absorption-enhancing factors Haem iron has high bioavailability and is minimally influenced by dietary factors. In contrast, several dietary factors influence non-haem iron absorption. Meat, fish and poultry contain not only the well-absorbed haem iron, but also MFP factor that promotes the absorption of nonhaem iron from other foods eaten at the same meal. Vitamin C also enhances non-haem iron absorption from foods eaten in the same meal by capturing the iron and keeping it in the reduced ferrous form, ready for absorption. Some acids and sugars also enhance non-haem iron absorption.

Absorption-inhibiting factors Some dietary factors bind with non-haem iron, inhibiting absorption. These factors include the phytates in legumes, whole grains and rice; the vegetable proteins in soybeans, other legumes and nuts; and the polyphenols (e.g. tannic acid) in tea, coffee, grain products, oregano and red wine.

CURRENT RESEARCH IN NUTRITION Gut bacteria’s role in iron absorption Iron deficiency is the most common and widespread nutritional disorder in the world, with the deficiency spanning both developing and industrialised countries. Strategies to increase the intake of foods rich in iron, as well as dietary factors that can enhance iron absorption, are therefore important to know about. As we learn more about how the gut microbiome can affect our health, scientists are now uncovering how bacterial species may boost iron absorption. One bacterium of interest is E. coli. While some strains of E. coli can cause illness, most are harmless and the human gastrointestinal tract is abundant with them. In recent laboratory experiments using a roundworm naturally rich in E. coli, when worms were fed E. coli genetically altered to lack the ability to produce a compound called enterobactin, they grew slowly and their iron levels were low.2 When enterobactin was re-introduced into the worms, natural growth resumed and iron levels rose. Enterobactin is important in binding and making iron available for the bacteria themselves, but this study shows that the bacteria can also help make iron available for the host as well. This opens up a new research field to see how modulating the gut microbiome with either prebiotics or probiotics designed to increase the beneficial E. coli species could help improve iron absorption.

Factors that enhance non-haem iron absorption are: • MFP factor • vitamin C (ascorbic acid) • gastric acidity. Factors that inhibit non-haem iron absorption are: • phytates (legumes, grains and rice) • vegetable proteins (soybeans, legumes, nuts) • t annic acid (and other polyphenols in tea and coffee) • reduced gastric acidity.

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Individual variation Overall, about 18 per cent of dietary iron is absorbed from mixed diets and only about 10 per cent from vegetarian diets.3 As you might expect, vegetarian diets do not have the benefit of easy-to-absorb haem iron or the help of MFP in enhancing absorption. In addition to dietary influences, iron absorption also depends on an individual’s health, stage in the life cycle and iron status, as well as on genetic variations in the expression of the central iron regulatory hormone hepcidin.4 Produced by the liver, hepcidin helps to maintain blood iron within the normal range by limiting absorption from the small intestine and controlling release from the liver, spleen and bone marrow. Hepcidin production increases in iron overload and decreases in iron deficiency. Absorption of iron can be as low as 2 per cent in a person with GI disease or as high as 35 per cent in a rapidly growing, healthy child. The body adapts to absorb more iron when a person’s iron stores fall short or when the need increases for any reason (e.g. pregnancy). The body makes more mucosal transferrin to absorb more iron from the intestines and more blood transferrin to carry more iron around the body. Similarly, when iron stores are sufficient, the body adapts to absorb less iron.

Shutterstock.com/kuslandia

Iron transport and storage The blood transport protein transferrin delivers iron to the bone marrow and other tissues. The bone marrow uses large quantities to make new red blood cells, whereas other tissues use less. Surplus iron is stored in the protein ferritin, primarily in the liver, but also in the bone marrow and spleen. When dietary iron has been plentiful, ferritin is constantly and rapidly made and broken down, providing an ever-ready supply of iron. When iron concentrations become abnormally high, the liver converts some ferritin into another storage protein called haemosiderin. Haemosiderin releases iron more slowly than ferritin does and storing excess iron in haemosiderin protects the body against the damage free iron can cause. Free iron acts as a free radical, attacking cell lipids, DNA and protein.

Iron recycling The average red blood cell lives about 4 months; then the spleen and liver cells remove it from the blood, take it apart and prepare the degradation products for excretion or recycling. The iron is salvaged: the liver attaches This chilli dinner provides several factors that may it to transferrin, which transports it back to the bone marrow to be enhance iron absorption – haem and non-haem iron reused in making new red blood cells. Thus, although red blood cells live and MFP from meat, non-haem iron from legumes, and vitamin C from tomatoes. for only about 4 months, the iron recycles through each new generation of cells (see Figure 13.3). The body loses some iron daily via the GI tract and, if bleeding occurs, in blood. Only tiny amounts of iron are lost in urine, sweat and shed skin. Iron excretion differs for men and women. On average, men and women lose about 1 milligram of iron per day, with women losing additional iron in menses. Menstrual losses vary considerably, but over a month they average about 0.5 milligrams of iron per day.

Iron deficiency Worldwide, iron deficiency is the most common nutrient deficiency, with iron-deficiency anaemia affecting 40 per cent of preschool-age children and pregnant woment.5 It is the only nutrient deficiency that is also significantly prevalent in industrialised countries. In many developing areas of the world this is frequently exacerbated by infectious diseases.

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FIGURE 13.3   Iron recycled in the body Once iron enters the body, most of it is recycled. Some is lost with body tissues and must be replaced by eating iron-containing food. Some losses via sweat, skin, and urine

Transferrin carries iron in blood. Some iron delivered to myoglobin of muscle cells

Liver (and spleen) dismantles red blood cells, packages iron into transferrin, and stores excess iron in ferritin (and haemosiderin).

Some losses if bleeding occurs

Bone marrow incorporates iron into haemosiderin of red blood cells and stores excess iron in ferritin (and haemosiderin).

Iron-containing haemoglobin in red blood cells carries oxygen.

Iron deficiency is also relatively common among those who are overweight and obese. The association between iron deficiency and obesity has yet to be explained, but researchers are currently examining the relationships between inflammation, hepcidin, and reduced iron absorption.6 Preventing and correcting iron deficiency are high priorities. Depletion of iron stores and iron deficiency occur in all age groups, particularly in groups of the population such as children, women after the onset of menstruation, elderly people, vegetarians (especially vegans) and in disadvantaged populations such as Aboriginal and Torres Strait Islander peoples, refugees, recent migrants and institutionalised people.

Vulnerable stages of life Some stages of life demand more iron but provide less, making deficiency likely. Women in their reproductive years are especially prone to iron deficiency because of repeated blood losses during menstruation. Pregnancy demands additional iron to support the added blood volume, growth of the foetus and blood loss during childbirth. Infants and young children receive little iron from their high-milk diets, yet need extra iron to support their rapid growth. The rapid growth of adolescence, especially for males, and the menstrual losses of females, also demand extra iron that a typical teen diet may not provide. An adequate iron intake is especially important during these stages of life.

Blood losses Bleeding from any site incurs iron losses. As mentioned, menstrual losses can be considerable as they tap women’s iron stores regularly. In a person with an active ulcer, the bleeding may not be obvious, but even small chronic blood losses significantly deplete iron reserves. In

Groups with high risk for iron deficiency include: • w omen in their reproductive years • pregnant women • i nfants and young children • teenagers.

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The iron content of blood is about 50 mg/100 mL blood. A person donating 500 mL of blood loses about 250 mg of iron. The stages of iron deficiency are: • iron stores diminish • transport iron decreases • haemoglobin production declines.

developing countries, blood loss is often brought on by malaria and parasitic infections of the GI tract. People who donate blood regularly also incur losses and may benefit from iron supplements. As mentioned, menstrual losses can be considerable as they tap women’s iron stores regularly.

Assessment of iron deficiency Iron deficiency develops in stages. This section provides a brief overview of how to detect these stages, and Appendix E provides more details. In the first stage of iron deficiency, iron stores diminish. Measures of serum ferritin (in the blood) reflect iron stores and are most valuable in assessing iron status at this earliest stage. Unfortunately, serum ferritin increases with infections, which interferes with accurate diagnoses and estimates of prevalence. The second stage of iron deficiency is characterised by a decrease in transport iron: serum iron falls, and the iron-carrying protein transferrin increases (an adaptation that enhances iron absorption). Together, measurements of serum iron and transferrin can determine the severity of the deficiency – the more transferrin and the less iron in the blood, the more advanced the deficiency is. Transferrin saturation – the percentage of transferrin that is saturated with iron – decreases as iron stores decline. The third stage of iron deficiency occurs when the lack of iron limits haemoglobin production. Now the haemoglobin precursor, erythrocyte protoporphyrin, begins to accumulate as haemoglobin and haematocrit values decline. Haemoglobin and haematocrit tests are easy, quick and inexpensive, so they are the tests most commonly used in evaluating iron status. Their usefulness in detecting iron deficiency is limited, however, because they are late indicators. Furthermore, other nutrient deficiencies and medical conditions can influence their values.

Iron deficiency and anaemia

Iron-deficiency anaemia is a microcytic hypochromic anaemia. • micro = small • cytic = cell • hypo = too little • chrom = colour

Iron deficiency and iron-deficiency anaemia are not the same: people may be iron-deficient without being anaemic. The term iron deficiency refers to depleted body iron stores without regard to the degree of depletion or to the presence of anaemia. The term iron-deficiency anaemia refers to the severe depletion of iron stores that results in a low haemoglobin concentration. In iron-deficiency anaemia, haemoglobin synthesis decreases, resulting in red blood cells that are pale (hypochromic) and small (microcytic), as shown in Figure 13.4. Without adequate iron, these cells can’t carry enough oxygen from the lungs to the tissues. Energy metabolism in the cells falters. The result is fatigue, weakness, headaches, apathy, pallor and poor resistance to cold temperatures. Because haemoglobin is the bright red pigment of the blood, the skin of a fair person who is anaemic may become noticeably pale. In a darkskinned person, the tongue and eye lining, normally pink, are very pale. The fatigue that accompanies iron-deficiency anaemia differs from the tiredness a person experiences from a simple lack of sleep. People with anaemia feel fatigue only when they exert themselves. Consequently, their work productivity, voluntary activities, and athletic performance decline. Iron supplementation can relieve the fatigue and improve the body’s response to physical activity. (The iron needs of physically active people and the special iron deficiency known as sports anaemia are discussed in Chapter 14.)

Iron deficiency and behaviour Long before the red blood cells are affected and anaemia is diagnosed, a developing iron deficiency affects behaviour. Even at slightly lowered iron levels, energy metabolism is impaired and neurotransmitter synthesis is altered, reducing physical work capacity and mental productivity. Without the physical energy and mental alertness to work, plan, think, play, sing or learn, people simply do less. They have no obvious deficiency symptoms; they just appear unmotivated and apathetic.

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FIGURE 13.4   Normal blood cells and blood cells in iron-deficiency anaemia compared Normal red blood cell production

In iron deficiency

DNA synthesis and cell division begins

Haemoglobin synthesis begins

Haemoglobin synthesis intensifies, slowing DNA synthesis and cell division

Without iron, haemoglobin synthesis is impaired

Nucleus migrates to cell wall

Nucleus and all cell organelles leave the cell

Mature red blood cells are small, containing only cytoplasm packed with haemoglobin

Red blood cells in iron-deficiency anaemia are relatively smaller (microcytic) and pale (hypochromic)

Many of the symptoms associated with iron deficiency are easily mistaken for behavioural or motivational problems. Not all behavioural problems are caused by nutrient deficiencies, but poor nutrition is always a possible contributor to problems like these. When investigating a behavioural problem, check the adequacy of the diet and seek a routine physical examination before undertaking more expensive, and possibly more harmful, treatment options. If iron deficiency is the problem, then treatment with an iron-rich diet and iron supplements may improve mood, cognitive skills, and physical performance. The effects of iron deficiency on children’s behaviour are discussed further in Chapter 16.

Iron deficiency and pica A curious behaviour seen in some people who are iron-deficient, especially in women and children of low-income groups, is pica – the craving and consumption of ice, chalk, clay and other non-food substances. These substances contain no iron and cannot remedy a deficiency; in fact, clay actually inhibits iron absorption, which may explain the iron deficiency that accompanies pica.7 Pica is poorly understood. Its cause is unknown, but researchers hypothesise that it may be motivated by hunger, nutrient deficiencies, or an attempt to protect against toxins or microbes.

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Iron toxicity As mentioned earlier, too much iron can be toxic, and its levels in the body are closely regulated. Absorption normally decreases when iron stores are full. Even a diet that includes fortified foods usually poses no risk for most people, but some individuals are vulnerable to excess iron. Once considered rare, iron overload has emerged as an important disorder of iron metabolism and regulation.

Iron overload

The most likely cause of iron overload is a disorder known as haemochromatosis, which is caused by a genetic failure to prevent unneeded iron in the diet from being absorbed. Haemochromatosis is one of the most common hereditary diseases. Around one in 300 people has a genetic predisposition to this disease. People who use alcohol excessively are particularly vulnerable to iron overload because alcohol damages the small intestine, impairing its defences against absorbing excess iron. Just as insulin supports normal glucose homeostasis and its absence or ineffectiveness causes diabetes, the hormone hepcidin supports iron homeostasis and its deficiency or, rarely, its resistance, causes haemochromatosis. Other causes of iron overload include repeated blood transfusions (which bypass the intestinal defence), dietary overload from supplemental iron (which overwhelms the intestinal defence) and other rare metabolic disorders. Excess iron may cause haemosiderosis, a condition characterised by deposits of the iron storage protein haemosiderin in the liver, heart, joints and other tissues. Some of the signs and symptoms of iron overload are similar to those of iron deficiency: apathy, lethargy and fatigue. Therefore, taking iron supplements before assessing iron status is clearly unwise. Haemoglobin tests alone would fail to make the distinction because excess iron accumulates in storage. Measurements to assess iron overload include transferrin saturation and serum ferritin. Iron overload is characterised by a toxic accumulation of iron in the liver, heart, joints, and other tissues. Excess iron in these tissues causes free-radical damage. Infections are likely because viruses and bacteria thrive on iron-rich blood. Untreated iron overload can lead to cirrhosis, liver cancer, heart failure, and arthritis. In addition to selecting a low-iron diet and limiting absorption-enhancing factors, treatment involves phlebotomy, which removes blood from the body, and chelation therapy, which uses a chelate to form a complex with iron and promote its excretion. Research targeting the activity of hepcidin is active and promising.8 Iron overload is much more common in men than in women and is twice as prevalent among men as is iron deficiency. The widespread fortification of foods with iron makes it difficult for people with haemochromatosis to follow a low-iron diet, and greater dangers lie in the indiscriminate use of iron and vitamin C supplements. Vitamin C not only enhances iron absorption but also releases iron from ferritin, allowing free iron to wreak the damage typical of free radicals. Thus, vitamin C acts as a pro-oxidant when taken in high doses.

Iron poisoning Large doses of iron supplements cause GI distress, including constipation, nausea, vomiting and diarrhoea. These effects may not be as serious as other consequences of iron toxicity, but they are consistent enough to establish an UL of 45 milligrams per day for adults. Ingestion of iron-containing supplements remains a leading cause of accidental poisoning in small children. Symptoms of toxicity include nausea, vomiting, diarrhoea, rapid heartbeat, weak pulse, dizziness, shock and confusion. As few as five iron tablets containing as little as 200 milligrams of iron have caused the deaths of dozens of young children. The exact cause of these deaths is uncertain, but excessive free-radical damage is thought to play a role in heart failure and respiratory distress. Autopsy reports reveal iron deposits and cell death in the stomach, small intestine, liver and blood vessels (which can cause internal bleeding). As with medicines and other potentially toxic substances, keep iron-containing tablets out of the reach

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of children. If you suspect iron poisoning, call the nearest poisons information centre or a doctor immediately.

PUTTING COMMON SENSE TO THE TEST

Iron recommendations and sources

Vegetarians require the same amount of iron in their diet as meat eaters. FALSE

The recommended daily intake of iron for men is 8 milligrams. Women in their reproductive years, however, need 18 milligrams a day. Because women have higher iron needs and lower energy needs, they sometimes have trouble obtaining enough iron. On average, women consume only 10 milligrams of iron per day, which is not enough iron for women until after menopause. To meet their iron needs from foods, premenopausal women need to select ironrich foods at every meal. People who follow a vegetarian diet need 1.8 times as much iron in their diet than meat eaters to make up for the lower iron bioavailability typical of their diets.9 Good non-animal sources of iron include soy foods (e.g. soybeans and tofu), legumes (e.g. lentils and kidney beans), nuts (e.g. cashews and almonds), seeds (e.g. pumpkin seeds and sunflower seeds), whole grains, dried fruits (e.g. apricots and raisins), and vegetables (e.g. mushrooms and potatoes). Combining these foods with foods high in vitamin C helps the body absorb the iron. Figure 13.5 shows the amounts of iron in selected foods. Meats, fish and poultry contribute the most iron per serving; other protein-rich foods, such as legumes and eggs, are also good sources. Although an indispensable part of the diet, foods in the milk group are notoriously poor in iron. Grain products vary, with wholegrain, enriched and fortified breads and cereals contributing significantly to iron intakes. Finally, dark greens (e.g. broccoli) and dried fruits (e.g. sultanas) contribute some iron.

Iron-fortified foods Iron is one of the fortification nutrients for grain products. One serving of fortified bread or cereal provides only a little iron, but because people eat many servings of these foods, the contribution can be significant. Iron added to foods is not absorbed as well as naturally occurring iron, but when eaten with absorption-enhancing foods, fortified iron can make a difference. In cases of iron overload, fortification may exacerbate the problem.

Maximising iron absorption To enhance iron absorption, be aware that the bioavailability of iron is high in meats, fish and poultry, intermediate in grains and legumes, and low in most vegetables, especially those containing oxalates, such as spinach. The amount of iron ultimately absorbed from a meal depends on the combined effects of several enhancing and inhibiting factors. For maximum absorption of non-haem iron, eat meat for MFP and fruits or vegetables for vitamin C. The iron of baked beans, for example, will be enhanced by the MFP in a slice of ham served with them. The iron in bread will be enhanced by the vitamin C in a slice of tomato on a sandwich.

Iron contamination and supplementation In addition to the iron from foods, contamination iron from non-food sources of inorganic iron salts can contribute to the day’s intakes. People can also get iron from supplements.

Contamination iron Foods cooked in iron cookware take up iron salts. The more acidic the food and the longer it is cooked in iron cookware, the higher the iron content. The iron content of eggs can triple in the time it takes to scramble them in an iron frying pan. Admittedly, the absorption of this iron may be poor (perhaps only 1 to 2 per cent), but every little bit helps a person who is trying to increase iron intake.

To calculate the Recommended Dietary Intake (RDI) for vegetarians, multiply by 1.8: • 8 mg × 1.8 = 14 mg/day (vegetarian men) • 18 mg × 1.8 = 32 mg/day (vegetarian women, 19 to 50 years).

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FIGURE 13.5   Iron in selected foods See the ‘How to’ box in Section 10.2, Chapter 10 for more information on using this figure. Milligrams Food

Serving size (kilojoules)

Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg Excellent sources: Oysters, canned Beef liver Parsley

30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 1 ⁄2 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)

0

2

4

6

8

10

12

14

16

18

RDI for women 19–50

RDI for women 51+

RDI for men IRON Meats (brown), legumes (dark blue) and some vegetables (green) make the greatest contributions of iron to the diet.

Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule

85 g (525 kJ) 85 g fried (773 kJ) 1 cup raw (92 kJ)

Polara Studios, Inc.

Iron supplements People who are iron deficient may need supplements as well as an ironrich, absorption-enhancing diet. Many doctors routinely recommend iron supplements to pregnant women, infants and young children. Iron from supplements is less well absorbed than that from food, so the doses must be high. The absorption of iron taken as ferrous sulphate or as an iron chelate is better than that from other iron supplements. Absorption also improves when supplements are taken between meals, at bedtime on an empty stomach and with liquids (other than milk, tea or coffee, which inhibit absorption). Taking iron supplements in a single dose instead of several doses per day is equally effective and may improve a person’s willingness to take it regularly. There is no benefit to taking iron supplements with orange juice because An old-fashioned iron skillet adds iron to foods. vitamin C does not enhance absorption from supplements as it does from foods. Vitamin C enhances iron absorption by converting insoluble ferric iron in foods to the more soluble ferrous iron, and supplemental iron is already in the ferrous form. Constipation is a common side effect of iron supplementation; drinking plenty of water may help to relieve this problem. Most importantly, iron supplements should be taken only when prescribed by a doctor who has assessed an iron deficiency.

Chapter 13: The trace minerals

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Most of the body’s iron is in haemoglobin and myoglobin where it carries oxygen for use in energy metabolism. Some iron is also required for enzymes involved in a variety of reactions. Special proteins assist with iron absorption, transport and storage – all helping to maintain an appropriate balance because both too little and too much iron can be damaging. Iron deficiency is most common among infants and young children, teenagers, women of child-bearing age and pregnant women. Symptoms include fatigue and anaemia. Iron overload is most common in men. Haem iron, which is found only in meat, fish and poultry, is better absorbed than non-haem iron, which occurs in most foods. Non-haem iron absorption is improved by eating iron-containing foods with foods containing the MFP factor and vitamin C; absorption is limited by phytates and oxalates. The summary table presents a few iron facts.

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IRON Recommended Dietary Intake

Men: 8 mg/day Women: 18 mg/day (19–50 years)  8 mg/day (51+ years)

Upper Level of Intake

Adults: 45 mg/day

Chief functions in the body

Part of the protein haemoglobin, which carries oxygen in the blood; part of myoglobin in muscles, which makes oxygen available for muscle contraction; participates in energy metabolism

Significant sources

Red meats, fish, poultry, shellfish, eggs, legumes, dried fruits

Deficiency symptoms

Anaemia: weakness, fatigue, headaches; impaired work performance and cognitive function; impaired immunity; pale skin, nailbeds, mucous membranes and palm creases; concave nails; inability to regulate body temperature; pica

Toxicity symptoms

GI distress Iron overload: infections, fatigue, joint pain, skin pigmentation, organ damage

13.3 Zinc

Zinc is a versatile trace element required as a cofactor by more than 100 enzymes. Virtually all cells contain zinc, but the highest concentrations are found in muscle and bone.

Zinc roles in the body Zinc supports the work of thousands of proteins in the body. Among them are the metalloenzymes, which participate in a variety of metabolic processes, including the regulation of gene expression. In addition, zinc stabilises cell membranes and DNA, helping to strengthen antioxidant defences against free-radical attacks. Zinc also assists in immune function and in growth and development. In the pancreas, zinc participates in the synthesis, storage and release of the hormone insulin. Zinc interacts with platelets in blood clotting, affects thyroid hormone function, and influences behaviour and learning performance. It is needed to produce the active form of vitamin A (retinal) in visual pigments and the retinol-binding protein that transports vitamin A. It is essential for normal taste perception, wound healing, sperm production and foetal development. A zinc deficiency impairs all these and other functions, underlining the vast importance of zinc in supporting the body’s proteins.

Reminder: A cofactor is a substance that works with an enzyme to facilitate a chemical reaction.

Metalloenzymes that require zinc include those that: • help make parts of the genetic materials DNA and RNA • manufacture haem for haemoglobin • participate in essential fatty acid metabolism • release vitamin A from liver stores • metabolise carbohydrates • synthesise proteins • metabolise alcohol in the liver • dispose of damaging free radicals.

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Zinc absorption and metabolism The body’s handling of zinc resembles that of iron in some ways and differs in others. A key difference is the circular passage of zinc from the intestine to the body and back again.

Zinc absorption The rate of zinc absorption varies from about 15 to 40 per cent, depending on the amount of zinc consumed: as zinc intake increases, the rate of absorption decreases, and as zinc intake decreases, the rate of absorption increases. As with iron, dietary factors such as phytates influence absorption, limiting zinc’s bioavailability. Upon absorption into an intestinal cell, zinc has two options. Zinc may participate in the metabolic functions of the intestinal cell itself or, it may be retained within the cell by metallothionein until it is needed by the body. Metallothionein in the intestinal cells helps to regulate zinc absorption by holding it in reserve until the body needs zinc. Then metallothionein releases zinc into the blood, where it can be transported around the body. Metallothionein in the liver performs a similar role, binding zinc until other body tissues signal a need for it.

Zinc transport After being absorbed, some zinc eventually reaches the pancreas, where it is incorporated into many of the digestive enzymes that the pancreas releases into the intestine at mealtimes. The small intestine thus receives two doses of zinc with each meal – one from foods and the other from the zinc-rich pancreatic secretions. The recycling of zinc in the body from the pancreas to the intestine and back to the pancreas is referred to as the enteropancreatic circulation of zinc. Each time zinc circulates through the small intestine, it may be excreted in shed intestinal cells or absorbed into the body (see Figure 13.6). The body loses zinc primarily in faeces. Smaller losses occur in urine, shed skin, hair, sweat, menstrual fluids and semen.

FIGURE 13.6   Enteropancreatic circulation of zinc Some zinc from food is absorbed by the small intestine and sent to the pancreas to be incorporated into digestive enzymes that return to the small intestine. This cycle is called the enteropancreatic circulation of zinc.

Zinc in food

Mucosal cells in the intestine store excess zinc in metallothionein. The pancreas uses zinc to make digestive enzymes and secretes them into the intestine.

If the body needs zinc

Metallothionein releases zinc to albumin and transferrin for transport to the rest of the body.

If the body does not need zinc

Zinc is not absorbed and is excreted in shed intestinal cells instead. Thus, zinc absorption is reduced when the body does not need zinc.

Chapter 13: The trace minerals

Numerous proteins participate in zinc transport. Zinc’s main transport vehicle in the blood is the protein albumin. Some zinc also binds to transferrin – the same transferrin that carries iron in the blood. Diets that deliver more than twice as much iron as zinc leave too few transferrin sites available for zinc.

Zinc deficiency

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Plant foods are the best sources of zinc in the diet. FALSE

Severe zinc deficiencies are not widespread in industrialised countries in the absence of other diseases, but they can still occur in vulnerable groups – pregnant women, young children, the elderly and the poor. Stunted growth is a primary characteristic of zinc deficiency. Figure 13.7 shows the severe growth retardation and mentions the immature sexual development characteristic of zinc deficiency. In addition, zinc deficiency impairs the immune response, making infections likely – among them, pneumonia and GI tract infections, which worsen malnutrition (a classic downward spiral of events). Chronic zinc deficiency damages the central nervous system and brain and may lead to poor motor development and cognitive performance. Because zinc deficiency directly impairs vitamin A metabolism, vitamin A-deficiency symptoms often appear. Zinc deficiency also alters taste, causes loss of appetite, and slows wound healing – in fact, its symptoms are so pervasive that generalised malnutrition and sickness are likely to be the diagnosis.

Zinc toxicity High doses (over 50 mg) of zinc may cause vomiting, diarrhoea, headaches, exhaustion and other symptoms. The UL for adults is set at 40 milligrams based on zinc’s interference in copper metabolism.

FIGURE 13.7   Zinc-deficiency symptom – stunted growth The growth retardation known as dwarfism is rightly ascribed to zinc deficiency because it is partially reversible when zinc is restored to the diet.

Zinc recommendations and sources Figure 13.8 shows zinc amounts in foods per serving. Zinc is highest in protein-rich foods, such as shellfish (especially oysters), meats, poultry, milk and cheese. Plant-based diets tend to be low in zinc, although legumes and wholegrain products are good sources of zinc if eaten in large quantities. Vegetables vary in zinc content depending on the soil in which they are grown. The requirement for dietary zinc may be as much as 50 per cent greater for people who follow a vegetarian diet, particularly strict vegetarians whose major staples are grains and legumes.

In developed countries, most people obtain enough zinc from the diet without resorting to supplements. In developing countries, zinc supplements play a major role in the treatment of childhood infectious diseases. Zinc supplements effectively reduce the incidence of disease and death associated with diarrhoea and pneumonia. The use of zinc lozenges to treat the common cold has been controversial and inconclusive, with some studies finding them effective and others not. Lozenges of zinc acetate or zinc gluconate seem to be the most effective, whereas other zinc compounds, including those with flavour enhancers, are much less effective. Common side effects of zinc lozenges include nausea and bad taste reactions.

H. Sandstead

Zinc supplementation

The on theman right on is an adult of average height. Theman Egyptian the right is an adult of The boy on the leftThe is 17Egyptian years old boy but is average height. ononly thethe left is height of an genitalia are 17 years oldaverage but is seven-year-old. only 4 feet tall,His like a seven-year-old in the United States. His like those of a six-year-old.

genitalia are like those of a six-year-old.

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Understanding Nutrition

FIGURE 13.8   Zinc in selected foods See the ‘How to’ box in Section 10.2, Chapter 10 for more information on using this figure. Milligrams Food

Serving size (kilojoules)

Bread, whole wheat Cornflakes Spaghetti pasta

30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ)

0

2

4

6

8

10

12

RDI for men

1 25 cm-round (983 kJ) ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ)

Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg

1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)

Excellent sources: Oysters Sirloin steak, lean Crab

85 g cooked (584 kJ) 85 g broiled (722 kJ) 85 g cooked (399 kJ)

14

1

1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ)

RDI for women

ZINC Meat, fish and poultry (brown) are concentrated sources of zinc. Milk (white) and legumes (dark blue) contain some zinc. Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule

APPLICATIONS OF NUTRITION RESEARCH Despite the popularity of zinc supplements, controversy over their effectiveness in treating the common cold has raged for decades. In a recent systematic review and meta-analysis, researchers attempted to sort through the confusion.10 The review looked at data from seven clinical trials and concluded that zinc supplements given within hours of onset of the symptoms of a cold can reduce the duration and severity of the illness by a third. There was no evidence that zinc doses over 100 mg/day can lead to greater benefit in the treatment of the common cold, with most trials using doses in the range of 80 to 92 mg. Both zinc acetate and zinc gluconate formulations showed a benefit with a slight, non-significant greater benefit seen with the zinc acetate form. Even with the positive findings outlined from this systematic review because of the differences in study populations, dosages, formulations and duration of treatment, it is difficult at this stage to make firm recommendations about the dose, formulation and duration that should be used for the general public.

Angel Tucker

Zinc and the common cold

Zinc is highest in protein-rich foods, such as oysters, beef, poultry, legumes and nuts.

Chapter 13: The trace minerals

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Zinc-requiring enzymes participate in a multitude of reactions affecting growth, vitamin A activity and pancreatic digestive enzyme synthesis, among others. After a meal, both dietary zinc and zinc-rich pancreatic secretions (via enteropancreatic circulation) are available for absorption. Absorption is regulated by a special binding protein (metallothionein) in the small intestine. Protein-rich foods derived from animals are the best sources of bioavailable zinc. Fibre and phytates in cereals bind zinc, limiting absorption. Stunted growth is a hallmark symptom of zinc deficiency. These facts and others are included in the following table.

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ZINC Recommended Dietary Intake

Men: 14 mg/day Women: 8 mg/day

Upper Level of Intake

Adults: 40 mg/day

Chief functions in the body

Part of many enzymes; associated with the hormone insulin; involved in making genetic material and proteins, immune reactions, transport of vitamin A, taste perception, wound healing, the making of sperm and normal foetal development

Significant sources

Protein-containing foods: red meats, shellfish, whole grains; some fortified cereals

Deficiency symptoms

Stunted growth, delayed sexual maturation, impaired immune function, hair loss, eye and skin lesions, loss of appetite

Toxicity symptoms

Loss of appetite, impaired immunity, low HDL, copper and iron deficiencies

13.4 Iodine

Traces of the iodine ion (called iodide) are indispensable to life. In the GI tract, iodine from foods becomes iodide. This chapter uses the term iodine when referring to the nutrient in foods and iodide when referring to it in the body.

The ion form of iodine is called iodide. Thyroidstimulating hormone is also called thyrotropin.

FIGURE 13.9  Iodine-deficiency symptom – an enlarged thyroid In iodine deficiency, the thyroid gland enlarges – a condition known as simple goitre. Iodine toxicity also enlarges the thyroid gland, creating a similar looking goitre.

Iodide roles in the body Iodide is an integral part of the thyroid hormones that regulate body temperature, metabolic rate, reproduction, growth, blood cell production, nerve and muscle function, and more. The thyroid gland releases tetraiodothyronine (T4), commonly known as thyroxine, to its target tissues. Upon reaching the cells, T4 is deiodinated to triiodothyronine (T3) within cells by deiodinases. T3 is the active form of the hormone and is three to four times more potent than T4.

The hypothalamus regulates thyroid hormone production by controlling the release of the pituitary’s thyroid-stimulating hormone (TSH). In an iodine deficiency, thyroid hormone production declines and the body responds by secreting more TSH in a futile attempt to accelerate iodide uptake by the thyroid gland. If a deficiency persists, the cells of the thyroid gland enlarge to trap as much iodide as possible. Sometimes the gland enlarges until it makes a visible lump in the neck, a simple goitre (shown in Figure 13.9). Almost all cases of goitre are caused by iodine deficiency. A relatively small percentage of the world’s population have goitre because they regularly eat excessive amounts of foods that contain an antithyroid

Science Source/Scott Camazine

Iodine deficiency

In iodine deficiency, the thyroid gland enlarges – a condition known as simple goitre. Iodine toxicity also enlarges the thyroid gland, creating a similarlooking goitre.

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Examples of goitrogen-containing foods are: • cabbage, spinach, radishes, swedes • soybeans, peanuts • peaches, strawberries.

The underactivity of the thyroid gland is known as hypothyroidism and may be caused by iodine deficiency. Without treatment, an infant with congenital hypothyroidism will develop the physical and mental retardation of congenital iodine deficiency.

PUTTING COMMON SENSE TO THE TEST

substance (goitrogen) whose effect is not counteracted by dietary iodine. The goitrogens present in plants remind us that even natural components of foods can cause harm when eaten in excess. Goitre may be the earliest and most obvious sign of iodine deficiency, but the most tragic and prevalent damage occurs in the brain. Iodine deficiency is the most common cause of preventable mental impairment and brain damage in the world. Nearly one-third of the world’s school-age children have iodine deficiency. Children with even a mild iodine deficiency typically have goitres and perform poorly in school. With sustained treatment, however, mental performance in the classroom as well as thyroid function improve. Mild iodine deficiency has re-emerged in Australia and New Zealand as a major public health issue in the last two decades. Even a mild form of iodine deficiency can give rise to hypothyroidism with symptoms of fatigue, goitre, mental impairment, depression, weight gain, and low basal body temperatures. Because of the re-emergence of iodine deficiency, from September 2009, Food Standards Australia New Zealand (FSANZ) introduced mandatory iodine fortification into the food supply using iodised salt in bread as the vehicle. Iodised salt is now added to all commercially sold bread in Australia and New Zealand, with the exception of organic and unleavened bread. An evaluation study into the impact of the mandatory iodine fortification program in Australia found people who were regular eaters of bread were 5-times more likely to have an adequate intake of iodine.11 But there were differences with people from a lower socioeconomic background less likely to get sufficient iodine in their diet. A severe iodine deficiency during pregnancy causes the extreme and irreversible cognitive and physical impairment with the condition known as congenital iodine deficiency or cretinism. Congenital iodine deficiency affects approximately 2 million children worldwide every year. A worldwide effort to provide iodised salt to people living in iodine-deficient areas has been dramatically successful. An estimated 70 per cent of all households in developing countries have access to iodised salt.12 Because iron deficiency is common among people with iodine deficiency and because iron deficiency reduces the effectiveness of iodised salt, dual fortification with both iron and iodine may be most beneficial.

Iodine toxicity

TRUE

Excessive intakes of iodine can interfere with thyroid function and enlarge the glands, just as deficiency can. During pregnancy, exposure to excessive iodine from foods, prenatal supplements or medications is especially damaging to the developing infant. An infant exposed to toxic amounts of iodine during gestation may develop a goitre so severe as to block the airways and cause suffocation. The UL is 1100 micrograms per day for an adult – several times higher than average intakes. For perspective, most foods provide 3 to 75 micrograms of iodine per serving.

Craig M. Moore

Seafood is a good source of iodine.

Only ‘iodised salt’ (right) has had iodine added.

On average, half a teaspoon of iodised salt provides the RDI for iodine.

Iodine recommendations and sources The ocean is the world’s major source of iodine. In coastal areas, seafood, water and even iodine-containing sea mist are dependable iodine sources. Further inland, the amount of iodine in foods is variable and generally reflects the amount present in the soil in which plants are grown or on which animals graze. Landmasses that were once under the ocean have soils rich in iodine; those in flood-prone areas where water leaches iodine from the soil are poor in iodine. Most soils in New Zealand are low in iodine, resulting in low concentrations in locally grown foods. Some countries add iodine to bread, fish paste or drinking water instead. The recommended intake of iodine for adults is a minuscule amount that is easily met by consuming seafood, seaweed, dairy products, vegetables grown in iodine-rich soil, and iodised salt. In Australia and New Zealand, labels indicate whether salt is iodised.

Chapter 13: The trace minerals

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Iodide is an essential component of thyroid hormone. An iodine deficiency can lead to simple goitre (enlargement of the thyroid gland) and can impair foetal development, causing congenital iodine deficiency. Iodine fortification has now been introduced into Australia and New Zealand to combat iodine deficiency. The following table provides a summary of iodine.

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IODINE Recommended Dietary Intake

Adults: 150 µg/day

Upper Level of Intake

1100 µg/day

Chief functions in the body

A component of two thyroid hormones that help to regulate growth, development and metabolic rate

Significant sources

Iodised salt, seafood, seaweed, bread, plants grown in iodine-rich soil and animals fed those plants

Deficiency disease

Simple goitre, congenital iodine deficiency

Deficiency symptoms

Underactive thyroid gland, goitre, mental and physical retardation in infants

Toxicity symptoms

Underactive thyroid gland, elevated TSH, goitre

13.5 Selenium

The essential mineral selenium shares some of the chemical characteristics of the mineral sulphur. This similarity allows selenium to substitute for sulphur in the amino acids methionine, cysteine and cystine.

Selenium roles in the body Selenium is one of the body’s antioxidant nutrients, working primarily as a part of proteins – most notably, the enzyme glutathione peroxidase. Glutathione peroxidase and vitamin E work in tandem. Glutathione peroxidase prevents free-radical formation, thus blocking the chain reaction before it begins; if free radicals do form and a chain reaction starts, vitamin E stops it. Another important role of selenium is in the conversion of thyroxine (T4) to triiodothyronine (T3) where selenium is a part of the deiodinases enzymes.

Key antioxidant nutrients are vitamin C, vitamin E, beta-carotene and selenium.

Selenium deficiency Selenium deficiency is associated with a heart disease that is prevalent in regions of China where the soil and foods lack selenium. Although the primary cause of this heart disease is probably a virus, selenium deficiency appears to predispose people to it, and adequate selenium seems to prevent it. Symptoms of selenium deficiency include impaired cognition and poor immunity. Selenium deficiency, though, is quite rare in healthy, well-nourished individuals. Deficiency has been seen in people with severely compromised intestinal function and in those of advanced age.

Selenium and cancer Some research suggests that selenium may protect against some types of cancers, though more recent findings do not support the use of this supplement in the primary prevention of cancer.13 However, given the potential for harm and the lack of conclusive evidence, recommendations to take selenium supplements would be premature – and perhaps ineffective as well. Selenium from foods appears to be more effective in inhibiting cancer growth than selenium from supplements. Such a finding reinforces a theme that has been repeated throughout this text – foods offer many more health benefits than supplements.

The heart disease associated with selenium deficiency is named Keshan disease for one of the provinces of China where it was studied. Keshan disease is characterised by heart enlargement and insufficiency; fibrous tissue replaces the muscle tissue that normally composes the middle layer of the walls of the heart.

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Selenium recommendations and sources Selenium is found in the soil, and therefore in the crops grown for consumption. People living in regions with selenium-poor soil may still get enough selenium, partly because they eat vegetables and grains transported from other regions, and partly because they eat meats and other animal products, which are reliable sources of selenium. In Australia and New Zealand, the main dietary sources of selenium are seafood, meat, poultry and eggs. New Zealand has a low soil selenium content, meaning that dietary intake of this nutrient is lower than in many other countries.

Selenium toxicity The body carefully regulates selenium metabolism and transport to help ensure a healthy balance. Because high doses of selenium are toxic, a UL has been set. Selenium toxicity causes loss and brittleness of hair and nails, garlic breath odour and nervous system abnormalities. Extreme cases of toxicity can result in cirrhosis of the liver, pulmonary oedema and death.

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Selenium is an antioxidant nutrient that works closely with the glutathione peroxidase enzyme and vitamin E. It is found in association with protein in foods. Deficiencies are associated with a predisposition to a type of heart abnormality known as Keshan disease. See the table below for a summary of selenium. SELENIUM Recommended Dietary Intake

Men: 70 µg/day Women: 60 µg/day

Upper Level of Intake

Adults: 400 µg/day

Chief functions in the body

Antioxidant; regulates thyroid hormone

Significant sources

Seafood, meat, whole grains, fruits and vegetables (depending on soil content)

Deficiency symptoms

Predisposition to heart disease characterised by cardiac tissue becoming fibrous (Keshan disease)

Toxicity symptoms

Loss and brittleness of hair and nails; skin rash, fatigue, irritability and nervous system disorders; garlic breath odour

13.6 Copper

The body contains about 100 milligrams of copper in a variety of cells and tissues. Copper balance and transport depend on a system of proteins.

Copper roles in the body Copper-containing enzymes have diverse metabolic roles with one common characteristic: all involve reactions that consume oxygen or oxygen radicals. For example, copper-containing enzymes catalyse the oxidation of ferrous iron to ferric iron, which allows iron to bind to its transport protein transferrin. Copper’s role in iron metabolism makes it a key factor in haemoglobin synthesis. Copper- and zinc-containing enzymes participate in the body’s natural defences against the oxidative damage caused by free radicals. Still other copper enzymes help to manufacture collagen, inactivate histamine, and degrade serotonin. Copper, like iron, is needed in many of the reactions involved in energy metabolism.

Chapter 13: The trace minerals

Copper deficiency and toxicity Typical Australian and New Zealand diets provide adequate amounts of copper, and deficiency is rare. In animals, copper deficiency raises blood cholesterol and damages blood vessels, raising questions about whether low dietary copper might contribute to cardiovascular disease in humans. Excessive intakes from foods are unlikely, but some genetic disorders can create a copper toxicity. Excessive intakes from supplements may cause liver damage, and therefore a UL has been set. Two rare genetic disorders affect copper status in opposite directions. In Menkes disease, the intestinal cells absorb copper, but cannot release it into circulation, causing a life-threatening deficiency. Treatment involves giving copper intravenously. In Wilson disease, copper accumulates in the liver and brain, creating a life-threatening toxicity. Wilson disease can be controlled by reducing copper intake, using chelating agents, such as penicillamine, and taking zinc supplements, which interfere with copper absorption. (The use of chelation in healthcare is mentioned in Highlight 18’s discussion of alternative therapies.)

Copper recommendations and sources The richest food sources of copper are legumes, whole grains, nuts, shellfish and seeds. More than half of the copper from foods is absorbed, and the major route of elimination appears to be bile. Water may also provide copper, depending on the type of plumbing pipe and the hardness of the water. The NRV Working Party found there was insufficient evidence to set an RDI for copper intake, so an Adequate Intake (AI) was set instead, based on median intake from Australian and New Zealand national dietary surveys.14

COPPER Adequate Intake

Men: 1.7 mg/day Women: 1.2 mg/day

Upper Level of Intake

Adults: 10 mg/day

Chief functions in the body

Participates in reactions that consume oxygen or oxygen radicals

Significant sources

Seafood, nuts, whole grains, seeds, legumes

Deficiency symptoms

Anaemia, bone abnormalities

Toxicity symptoms

Liver damage

13.7 Manganese

The human body contains a tiny 20 milligrams of manganese. Most of it can be found in the bones and metabolically active organs, such as the liver, kidneys and pancreas.

Manganese roles in the body Manganese acts as a cofactor for many enzymes that facilitate the metabolism of carbohydrate, lipids and amino acids. In addition, manganese-containing metalloenzymes assist in bone formation and the conversion of pyruvate to a TCA cycle compound.

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Copper is a component of several enzymes, all of which are involved in some way with oxygen or oxidation. Some act as antioxidants; others are essential to iron metabolism. Legumes, whole grains and shellfish are good sources of copper. See the table below for a summary of copper facts.

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Manganese deficiency and toxicity Manganese requirements are small, and many plant foods contain significant amounts of this trace mineral, so deficiencies are rare. As is true of other trace minerals, however, dietary factors, such as phytates, inhibit its absorption. In addition, high intakes of iron and calcium limit manganese absorption, so people who use supplements of those minerals regularly may impair their manganese status. Manganese toxicity is more likely to occur from environmental contamination than from excessive dietary intakes. Miners who inhale large quantities of manganese dust over prolonged periods show symptoms of a brain disease, along with abnormalities in appearance and behaviour. The NRV Working Party did not specify a UL due to insufficient evidence to set a level with certainty.

Manganese recommendations and sources Grain products make the greatest contribution of manganese to the diet. With insufficient information to establish an RDI, an Adequate Intake (AI) was set based on average intakes.

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Manganese-dependent enzymes are involved in bone formation and various metabolic processes. Because manganese is widespread in plant foods, deficiencies are rare, although regular use of calcium and iron supplements may limit manganese absorption. A summary of manganese appears in the table below. MANGANESE Adequate Intake

Men: 5.5 mg/day Women: 5 mg/day

Upper Level of Intake

None specified

Chief functions in the body

Cofactor for several enzymes; bone formation

Significant sources

Nuts, whole grains, leafy vegetables, tea

Deficiency symptoms

Rare

Toxicity symptoms

Nervous system disorders

13.8 Fluoride

Fluoride is present in virtually all soils, water supplies, plants and animals. The body contains only a trace of fluoride, but this amount is necessary for perfect tooth formation.

Fluoride roles in the body The key bone nutrients are: • vitamin D, vitamin K, vitamin A • calcium, phosphorus, magnesium, fluoride.

As Chapter 12 explains, during the mineralisation of bones and teeth, calcium and phosphorus form crystals called hydroxyapatite. Fluoride can replace the hydroxyl (OH) portions of the hydroxyapatite crystal, forming fluorapatite, which makes the bones stronger and the teeth more resistant to decay. Dental caries, which can go on to result in teeth that require fillings or that are missing, rank as one of the most common and widespread health problems. An estimated 95 per cent of the population has decayed, missing or filled teeth. These dental problems can quickly lead to a multitude of nutrition problems by interfering with a person’s ability to chew and eat a wide variety of foods. Where fluoride is lacking, dental decay is common. Drinking water is usually the best source of fluoride. Fluoridation of drinking water protects against dental caries and supports oral health. The combined use of fluoride toothpaste and fluoridated water offers more protection than using either separately. Both

Chapter 13: The trace minerals

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drinking water and toothpaste provide important and complementary benefits. The drinking water provides long low-level protection, but the fluoride in toothpaste is at a high enough concentration that it has additional properties. Most bottled waters lack fluoride. Because of the low natural levels of fluoride in some water supplies and high levels of dental caries, many authorities worldwide, including in Australia and New Zealand, have instigated fluoridation of water supplies. Concentrations in fluoridated areas are within the range identified as safe and effective, varying from 0.6 mg/L in Darwin to 1.1 mg/L in Hobart.15 In New Zealand, the Ministry of Health has recommended fluoridation of water supplies since the 1950s as the most effective and efficient way of preventing dental caries in communities receiving a reticulated water supply. Around 85 per cent of the New Zealand population uses what the government considers to be satisfactorily safe community water supplies in terms of fluoride content.

Bottled water is a good source of fluoride.

FALSE

FIGURE 13.10  Fluoride-toxicity symptom – the mottled teeth of fluorosis

Fluoride toxicity

Science Source/Dr. P. Marazzi

Too much fluoride can damage the teeth, causing fluorosis. For this reason, a UL has been established. In mild cases, the teeth develop small white specks; in severe cases, the enamel becomes pitted and permanently stained (as shown in Figure 13.10). Fluorosis occurs only during tooth development and cannot be reversed, making its prevention a high priority. Fluorosis can also affect the skeleton, causing an increase in bone mass, joint pain and stiffness, and even deformities of the spine and major joints. To limit fluoride ingestion, take care not to swallow fluoridecontaining dental products, such as toothpaste and mouthwash.

Fluoride recommendations and sources As mentioned earlier, many people in Australia and New Zealand have access to water with an optimal fluoride concentration, which typically delivers about 1 milligram per person per day. Fish and most teas contain appreciable amounts of natural fluoride.

FLUORIDE Adequate Intake

Men: 4 mg/day Women: 3 mg/day

Upper Level of Intake

Adults: 10 mg/day

Chief functions in the body

Strengthens teeth; helps to make teeth resistant to decay

Significant sources

Drinking water (if fluoride-containing or fluoridated), tea, seafood

Deficiency symptoms

Susceptibility to tooth decay

Toxicity symptoms

Fluorosis (pitting and discoloration of teeth)

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Fluoride strengthens teeth and makes them more resistant to decay. Fluoridation of public water supplies can significantly reduce the incidence of dental caries, but excess fluoride during tooth development can cause fluorosis, which causes discoloured and pitted tooth enamel. The table below summarises fluoride information.

To prevent fluorosis: • monitor the fluoride content of the local water supply • supervise toddlers when they brush their teeth, using only a small amount of toothpaste (peasize amount) • use fluoride supplements only as prescribed by a doctor.

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13.9 Chromium

Chromium is an essential mineral that participates in carbohydrate and lipid metabolism. Like iron, chromium assumes different charges. In chromium, the Cr+++ ion is the most stable and most commonly found in foods.

Chromium roles in the body

Small organic compounds that enhance insulin’s action are called glucose tolerance factors (GTF). Some glucose tolerance factors contain chromium.

Chromium helps maintain glucose homeostasis by enhancing the activity of the hormone insulin. When chromium is lacking, a diabetes-like condition may develop with elevated blood glucose and impaired glucose tolerance, insulin response and glucagon response. Some research suggests that chromium supplements lower blood glucose or improve insulin responses in type 2 diabetes, but findings have not been consistent.16

Chromium recommendations and sources Chromium is present in a variety of foods. The best sources are unrefined foods, particularly liver, brewer’s yeast and whole grains. The more refined foods people eat, the less chromium they ingest. No UL for chromium has been established.

Chromium supplements Supplement advertisements have succeeded in convincing consumers that they can lose fat and build muscle by taking chromium picolinate. Whether chromium supplements (either picolinate or plain) reduce body fat or improve muscle strength remains controversial. (Highlight 14 revisits chromium picolinate and other supplements athletes use in the hopes of improving their performance.) REVIEW IT

Chromium enhances insulin’s action. A deficiency can impair glucose homeostasis. Chromium is widely available in unrefined foods including brewer’s yeast, whole grains and liver. The following table provides a summary of chromium. CHROMIUM Adequate Intake

Men: 35 µg/day Women: 25 µg/day

Upper Level of Intake

None specified

Chief functions in the body

Enhances insulin action, may improve glucose tolerance

Significant sources

Meats (especially liver), whole grains, brewer’s yeast

Deficiency symptoms

Diabetes-like condition (impaired glucose tolerance)

Toxicity symptoms

None reported

13.10 Molybdenum

Molybdenum acts as a working part of several metalloenzymes. Dietary deficiencies of molybdenum are unknown because the amounts needed are so small – as little as 0.1 parts per million parts of body tissue. Legumes, breads and other grain products, leafy green vegetables, milk and liver are molybdenum-rich foods. Average daily intakes fall within the suggested range of intakes. Molybdenum toxicity in people is rare. It has been reported in animal studies, and a UL has been established. Characteristics of molybdenum toxicity include kidney damage and reproductive abnormalities. For a summary of molybdenum facts, see the accompanying table.

Chapter 13: The trace minerals

Adults: 45 µg/day

Upper Level of Intake

Adults: 2000 µg/day

Chief functions in the body

Cofactor for several enzymes

Significant sources

Legumes, whole grains, nuts

Deficiency symptoms

Unknown

Toxicity symptoms

None reported; reproductive effects in animals

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MOLYBDENUM Recommended Dietary Intake

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13.11  Other trace minerals

Research to determine whether other trace minerals are essential is FIGURE 13.11   Cobalt with vitamin B12 difficult because their quantities in the body are so small and also because The intricate intricate vitamin vitamin B B12 molecule molecule contains contains The 12 human deficiencies are unknown. Guessing their functions in the body one atom atom of of the the mineral mineral cobalt. cobalt. The The alternative alternative one name for vitamin B , cobalamin, reflects the can be particularly problematic. Much of the available knowledge comes 12 name for vitamin B12, cobalamin, reflects the presence of of cobalt cobalt in in its its structure. structure. from research using animals. presence Some important trace minerals and their main functions include the following: NH2 NH 2 •  Nickel may serve as a cofactor for certain enzymes. C O O CN NH2 C CN NH •  Silicon is involved in the formation of bones and collagen. 2 H N CH2 H22N CH O NH2 C O • Vanadium is necessary for growth and bone development and for normal CH C 2 NH2 3 CH3 O C CH H C reproduction. CH O C CH22 3 C O O 2 H3C CH2 C H2C C • Cobalt is a key mineral in the large vitamin B12 molecule (see Figure 13.11), H 2 CH2 CH CH2 CH H3C C 2 but it is not an essential nutrient and no recommendation has been H 2 H 3 H N N H C N N established. H33C H Co++ H Co • Boron may play a key role in brain activities; in animals, boron strengthens N N bones. N N H O CH3 H O CH 3 In the future, we may discover that many other trace minerals play key C H C CH 2 C H2C CH33 nutritional roles. Even arsenic – famous as a poison used by murderers and CH CH2 CH CH2 CH2CH33 NH CH CH 2 2 2 known to be a carcinogen – may turn out to be essential for human beings in NH22 CH3 CH C O O CH 2 3 CH C 2 tiny quantities. CH3 O C O CH C 3 CH2 NH CH CH NH CH 2 O O–– O O Chapter 12 and this chapter have told of the many ways minerals serve the P P body – maintaining fluid and electrolyte balance, providing structural support O O O O

NH2 NH 2

Contaminant minerals

H OH H OH

N++ N

to the bones, transporting oxygen and assisting enzymes. In opposition to N H N H H H H the essential minerals that the body requires, contaminant minerals impair H H CH2 O the body’s growth, work capacity and general health. Contaminant minerals H CH 2 O OH OH include the heavy metals lead, mercury and cadmium that enter the food supply by way of soil, water and air pollution. This section focuses on lead poisoning because it is a serious environmental threat to young children. Much of the information on lead applies to the other contaminant minerals as well – they all disrupt body processes and impair nutrition status.

Lead Like other minerals, lead is indestructible; the body cannot change its chemistry. Because it is chemically similar to nutrient minerals such as iron, calcium and zinc (cations with two positive charges), lead displaces them from some of the metabolic sites they normally occupy,

H H

H H

CH3 CH 3 CH3 CH 3

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but is then unable to perform their tasks. For example, lead competes with iron in haem, but it cannot carry oxygen. Similarly, lead competes with calcium in the brain, but it cannot help nerve cells to transmit messages. Excess lead in the blood also deranges the structure of red blood cell membranes, making them fragile and leaky. Lead interacts with white blood cells too, impairing their ability to fight infection, and it binds to antibodies, thwarting their effort to resist disease. In addition to its effects on the blood, lead impairs many body systems, most notably causing irreversible damage to the central nervous system. In short, lead’s interactions in the body have profound adverse effects – the greater the exposure, the more damaging the effects. Table 13.1 lists symptoms of lead toxicity. Children with iron deficiency are particularly vulnerable to lead toxicity. Chelation agents may be prescribed to efficiently excrete lead and other heavy metals from the body. Chapter 16 examines the damaging effects of iron deficiency and lead toxicity on children’s growth and development. Chapter 19 includes mercury in its discussion of environmental contamination of foods.

TABLE 13.1   Symptoms of lead toxicity IN CHILDREN Learning disabilities (reduced short-term memory; impaired concentration) Low IQ Behaviour problems Slow growth Iron-deficiency anaemia Dental caries Sleep disturbances (night-waking, restlessness, head-banging) Nervous system disorders, seizures Slow reaction time, poor coordination Impaired hearing IN ADULTS Hypertension Reproductive complications Kidney failure

Closing thoughts on the nutrients This chapter completes the introductory lessons on the nutrients. Each nutrient from the amino acids to zinc has been described rather thoroughly – its chemistry, roles in the body, sources in the diet, symptoms of deficiency and toxicity, and influences on health and disease. Such a detailed examination is informative, but it can also be misleading. It is important to step back from the detailed study of the individual nutrients to look at them as a team. After all, people eat foods not nutrients, and most foods deliver dozens of nutrients. Furthermore, nutrients work cooperatively with each other in the body; their actions are most often interactions. This chapter alone mentioned how iron depends on vitamin C to keep it in its active form and on copper to incorporate it into haemoglobin, how zinc is needed to activate and transport vitamin A, and how both iodine and selenium are needed for the synthesis of thyroid hormone. The following table provides a review of the trace minerals.

Chapter 13: The trace minerals

MINERAL AND CHIEF FUNCTIONS

DEFICIENCY SYMPTOMS

TOXICITY SYMPTOMSa

SIGNIFICANT SOURCES

Anaemia: weakness, fatigue, headaches; impaired work performance; impaired immunity; pale skin, nail beds, mucous membranes and palm creases; concave nails; inability to regulate body temperature; pica

GI distress; iron overload: infections, fatigue, joint pain, skin pigmentation, organ damage

Meats, fish, poultry, shellfish, eggs, legumes, dried fruits

Stunted growth, delayed sexual maturation, impaired immune function, hair loss, eye and skin lesions, loss of appetite

Loss of appetite, impaired immunity, low HDL, copper and iron deficiencies

Protein-containing foods: red meats, fish, shellfish, poultry, whole grains; fortified cereals

Underactive thyroid gland, goitre, mental and physical retardation

Underactive thyroid gland, elevated TSH, goitre

Iodised salt; seafood and seaweed; plants grown in iodine-rich soil and animals fed those plants

Associated with Keshan disease (heart disease characterised by cardiac tissue becoming fibrous)

Nail and hair brittleness and loss; fatigue, irritability and nervous system disorders; skin rash, garlic breath odour

Seafood, meat, whole grains, fruits and vegetables (depending on soil content)

Anaemia, bone abnormalities

Liver damage

Seafood, nuts, legumes, whole grains, seeds

Rare

Nervous symptom disorders

Nuts, whole grains, leafy vegetables, tea

Susceptibility to tooth decay

Fluorosis (pitting and discoloration) of teeth

Drinking water (if fluoridated), tea, seafood

Impaired glucose tolerance

None reported

Meats (especially liver), whole grains, brewer’s yeast

Unknown

None reported

Legumes, whole grains, nuts

Iron Part of the protein haemoglobin, which carries oxygen in the blood; part of the myoglobin in muscles, which makes oxygen available for muscle contraction; participates in energy metabolism Zinc Part of many enzymes; associated with the hormone insulin; involved in making genetic material and proteins, immune reactions, transport of vitamin A, taste perception, wound healing, sperm production and normal foetal development Iodine A component of the thyroid hormones that help to regulate growth, development and metabolic rate Selenium Antioxidant; regulates thyroid hormone

Copper Participates in reactions that consume oxygen or oxygen radicals Manganese Cofactor for several enzymes; bone formation Fluoride Strengthens teeth; helps to make teeth resistant to decay Chromium Enhances insulin action, may improve glucose intolerance Molybdenum Cofactor for several enzymes a

Acute toxicities of many minerals cause abdominal pain, nausea, vomiting and diarrhoea.

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The trace minerals

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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Iron from animal foods is normally absorbed better than iron from plant foods. TRUE

Iron in the haem form, which is found in foods derived from the flesh of animals, is more absorbable than iron found in plant foods.

2 Vegetarians require the same amount of iron in their diet as meat eaters. FALSE

Because the overall bioavailability of iron from plant-based diets is less than that from mixed diets, vegetarians have 80 per cent higher requirements for dietary iron intake.

3 Plant foods are the best sources of zinc in the diet. FALSE

Zinc is highest in protein-rich foods, such as shellfish, meats, poultry, milk and cheese. Plant-based diets tend to be low in zinc.

4 Seafood is a good source of iodine. TRUE

The ocean is the world’s major source of iodine, so seafood and even seaweed are good sources of iodine.

5 Bottled water is a good source of fluoride. FALSE

Most bottled water lacks fluoride. Fluoridated drinking water is the best source of fluoride in our diet.

NUTRITION PORTFOLIO Trace minerals from a variety of foods, especially those in the meat and meat alternative group, support many of the body’s activities. • Examine the variety in your food intake, taking particular notice of how often you include meats,

• •

seafood, poultry or legumes, weekly. Estimate how much iron and zinc these foods provide for you. Describe the advantages of using iodised salt. Determine if your water supply is fluoridated and if so, at what level.

STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1

High fibre intake. Iron being in a non-haem form. Having low iron stores. Drinking milk.

7

Three-year-old boy. 60-year-old woman. 24-year-old woman. 52-year-old man.

Which of the following provides the most absorbable iron? a b c d

85 g steak. ½ cup of spinach. 1 apple. 1 glass of milk.

anaemia goitre mottled teeth growth retardation.

A type of congenital deficiency resulting in cognitive and physical impairment in infants is caused by a deficiency of: a b c d

8

albumin ferritin haemosiderin metallothionein.

A classic sign of zinc deficiency is: a b c d

Which of the following people has the highest requirement for iron? a b c d

4

6

Which of the following factors can enhance intestinal iron absorption? a b c d

3

haem phytates vitamin C MFP factor.

The intestinal protein that helps to regulate zinc absorption is: a b c d

Iron absorption is impaired by: a b c d

2

5

iron zinc iodine selenium.

The mineral best known for its role as an antioxidant is: a b c d

copper selenium manganese molybdenum.

Chapter 13: The trace minerals

9

10 Which of the following minerals enhances insulin activity?

Fluorosis occurs when fluoride: a b c d

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is excessive is inadequate binds with phosphorus interacts with calcium.

a b c d

Zinc. Iodine. Chromium. Manganese.

REVIEW QUESTIONS 1

Describe the key dietary factors that can affect iron absorption. (Section 13.2)

6

Describe how the symptoms of zinc deficiency in children are related to its functions. (Section 13.3)

2

Distinguish between iron deficiency and irondeficiency anaemia. What are the symptoms of irondeficiency anaemia? (Section 13.2)

7

Describe the principal functions of iodide, selenium, copper, manganese, fluoride, chromium and molybdenum in the body. (Sections 13.4–13.10)

3

Describe the main features of iron overload and toxicity and how these could arise. (Section 13.2)

8

4

Describe why iron recommendations vary among different age groups and sex groups? What is the rationale for these differences? (Section 13.2)

What public health measure has been used in preventing simple goitre? What measure has been recommended for protection against tooth decay? (Sections 13.5, 13.11)

9

Discuss the importance of balanced and varied diets in obtaining the essential minerals and avoiding toxicities. (Section 13.11)

5

Describe the similarities and differences in the absorption and regulation of iron and zinc. (Sections 13.2, 13.3)

NUTRITION CALCULATIONS d e f g h I

Once you have mastered these examples, you will understand minerals better and be prepared to examine your own food choices. Be sure to show your calculations for each problem. Answers can be found at the back of this book. 1

For each of these minerals, note the unit of measure for recommendations: a b c

iron zinc iodine IRON (mg)

2

selenium copper manganese fluoride chromium molybdenum.

The iron density of foods can vary widely. In the following table is a list of foods with the energy amount and iron content per serving. Calculate the iron density (divide mg by kJ) for each of the foods and rank them by their iron per 1000 kilojoule content.

ENERGY (kJ)

Milk, full-fat, 1 cup

0.10

357

Cheddar cheese, 30 g

0.19

479

Broccoli, cooked from fresh, chopped, 1 cup

1.31

184

Sweet potato, baked in skin, 1 whole

0.51

491

Cantaloupe melon, 50 g

0.56

391

Carrots, fresh, ½ cup

0.48

147

Wholewheat bread, 1 slice

0.87

269

Green peas, ½ cup

1.26

260

Apple, 1 medium

0.38

525

Sirloin steak, lean, 115 g

3.81

958

Pork chop, lean, 90 g

0.66

697

IRON DENSITY (mg/1000 kJ)

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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Learn more about iron and the diseases caused by over- or under consumption at the Australian Government healthdirect site: http://www. healthdirect.gov.au/iron • Learn about the worldwide issue of anaemia from the World Health Organization, https://www.who.int/ health-topics/anaemia

• •

•

Search ‘minerals’ at the Dietitians Australia site: http://www.dietitiansaustralia.org.au Learn more about iodine and thyroid disease from the Australian Thyroid Foundation and the Thyroid Association of New Zealand: http://www. thyroidfoundation.org.au and http://www.thyroidnz.org Learn more about lead in the environment and its effect on health from the Lead Group: http://www. lead.org.au

Chapter 13: The trace minerals

13.12 PHYTOCHEMICALS AND FUNCTIONAL FOODS Chapter 13 completes the introductory discussions on the six classes of nutrients – carbohydrates, lipids, proteins, vitamins, minerals and water. In addition to these nutrients, foods contain thousands of non-nutrient compounds, including the phytochemicals. Chapter 1 introduced the phytochemicals as compounds found in plant-derived foods (phyto means plant) that have biological activity in the body. Research on phytochemicals is unfolding daily, adding to our knowledge of their roles in human health, but there are still many questions and only tentative answers. Just a few of the tens of thousands of phytochemicals have been researched at all, and only a sampling are mentioned in this Highlight – enough to illustrate their wide variety as food sources and roles in supporting health. The concept that foods provide health benefits beyond those of the nutrients emerged from numerous epidemiological studies showing the protective effects of plant-based diets on cancer and heart disease. People have been using foods to maintain health and prevent disease for years, but now these foods have been given a name – they are called functional foods. As Chapter 1 explains, functional foods include all foods (whole, fortified or modified foods) that exert potentially beneficial effects on health. Whole foods – as natural and familiar as oats or tomatoes – are the simplest functional foods. In some cases, foods have been modified to provide health benefits, perhaps by lowering the trans fat content. In other cases, manufacturers have fortified foods by adding nutrients or

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HIGHLIGHT

13

phytochemicals that provide health benefits. Examples of these functional foods include orange juice fortified with calcium to help build strong bones and margarine made with plant sterols that lowers blood cholesterol. Much of this text touts the benefits of nature’s functional foods, such as whole grains rich in dietary fibres, oily fish rich in omega-3 fatty acids, and fresh fruits rich in phytochemicals. This highlight begins with a look at foods, the phytochemicals they contain, and their roles in disease prevention. Then the discussion turns to examine the most controversial of functional foods – novel foods to which phytochemicals have been added to promote health. How these foods fit into a healthy diet is still unclear.

The phytochemicals In foods, phytochemicals impart tastes, aromas, colours and other characteristics. They give chilli peppers their burning sensation, garlic its pungent flavour and tomatoes their dark red colour. In the body, phytochemicals can have profound physiological effects – acting as antioxidants, mimicking hormones, stimulating enzymes, interfering with DNA replication, suppressing inflammation, destroying bacteria, and binding to cell walls. Any of these actions may prevent the development of chronic diseases, depending in part on how genetic factors interact with the phytochemicals. Phytochemicals might also have adverse effects when consumed in excess as a dietary supplement.

iStock.com/Tatiana Dyuvbanova

Defending against cancer

Vegetables are the best dietary sources of phytochemicals.

A variety of phytochemicals from a variety of foods appear to protect against DNA damage and defend the body against cancer.1 A few examples follow. Soybeans and products may protect against cancers.2 Soybeans are a rich source of isoflavones. The most abundant and active isoflavone in soy is genistein. Among its many actions in the body is to block the development of new blood vessels, which is key to limiting the growth, invasion and spread of cancer.3 Genistein also acts synergistically with some anticancer drugs, offering a potential benefit in combination therapy. Because the chemical structure of genistein is similar to that of the hormone oestrogen, it can mimic oestrogen activity or

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alter oestrogen synthesis and metabolism in the body. Soy foods appear to be most effective when consumed in moderation early and throughout life.4 However, the use of phytoestrogen supplements is ill-advised because of their much higher dosage of phytoestrogens, which may stimulate the growth of oestrogen-dependent cancers (e.g. breast cancer) and reduce the effectiveness of cancer treatments. The Cancer Council Australia does not recommend or support the use of phytoestrogen supplements for breast cancer survivors and advises that women with existing breast cancer or past breast cancer should be cautious in consuming large quantities of soy foods or phytoestrogen supplements.5 Limited evidence suggests that tomatoes may offer protection against cancers of the oesophagus, lungs, prostate and stomach. Among the phytochemicals responsible for this effect is lycopene, one of beta-carotene’s many carotenoid relatives. Lycopene is the pigment that gives apricots, guava, papaya, pink grapefruits and watermelon their red colour – and it is especially abundant in tomatoes and cooked tomato products. Lycopene is a powerful antioxidant that seems to inhibit the growth of cancer cells.6 Because food processing and cooking can improve absorption, cooked tomato products, such as spaghetti sauce, provide more lycopene than raw tomatoes. Soybeans and tomatoes are only two of the many fruits and vegetables credited with providing anticancer activity. Evidence suggests that the risk of many cancers, and perhaps of cancer in general, decreases when diets include an abundance of fruits and vegetables.7 To that end, current recommendations urge consumers to eat five servings of vegetables and two servings of fruit a day.

act as antioxidants and protect against heart disease by reducing inflammation and lowering blood pressure.

Defending against heart disease

Functional foods

Diets based primarily on fruits, vegetables, legumes and whole grains appear to support heart health better than those founded on highly refined foods – perhaps because of the abundance of nutrients, fibre or phytochemicals, such as the flavonoids.8 Flavonoids, a large group of phytochemicals known for their health-promoting qualities, are found in whole grains, legumes, soy, vegetables, fruits, herbs, spices, teas, chocolate, nuts, olive oil and red wines. Flavonoids are powerful antioxidants that may help to protect LDL cholesterol against oxidation, minimise inflammation and reduce blood platelet stickiness, thereby slowing the progression of atherosclerosis and defending against blood clots. The phytosterols of soybeans and the lignans of flaxseed may also protect against heart disease. These cholesterol-like molecules are naturally found in all plants and inhibit cholesterol absorption in the body. As a result, blood cholesterol levels decline.9 These phytochemicals also

The phytochemicals in perspective Most research on phytochemicals has focused on cancer and heart disease, but foods deliver thousands of phytochemicals in addition to dozens of nutrients that defend against other diseases as well. Researchers must be careful in giving credit for particular health benefits to any one compound. Diets rich in whole grains, legumes, vegetables, fruits and nuts seem to protect against heart disease and cancer, but identifying the specific foods or components of foods that are responsible is difficult. Each food possesses a unique array of phytochemicals – citrus fruits provide monoterpenes; grapes, resveratrol; cocoa, flavonoids; and flaxseed, lignans, to name just a few. Broccoli may contain as many as 10 000 different phytochemicals – each with the potential to influence some action in the body. Beverages, such as wine; spices, such as oregano; and oils, such as olive oil (especially extra virgin olive oil) contain many phytochemicals that may explain, in part, the observation that people who live in the Mediterranean region have reduced risks of heart disease and cancer. Phytochemicals might also explain why the DASH diet (described in Chapter 12) is so effective in lowering blood pressure and blood lipids. Even identifying all of the phytochemicals and their effects doesn’t answer all the questions because the actions of phytochemicals may be complementary or overlapping, which reinforces the principle of variety in diet planning. For an appreciation of the array of phytochemicals offered by a variety of fruits and vegetables, see Figure H13.1.

Because foods naturally contain thousands of phytochemicals that are biologically active in the body, virtually all of them have some special value in supporting health. In other words, even simple, whole foods, in reality, are functional foods. Ginger may quell nausea; blueberries may lower blood pressure; garlic may lower blood cholesterol; grapes may reduce inflammation; coffee may reduce the risk of prostate cancer; and black tea may protect against bone fractures, just to name a few examples. Functional foods rich in phytochemicals are easy to find in the produce section of the supermarket. Just look for the colourful fruits and vegetables (see Table H13.1). But food manufacturers continue to concoct special ‘functional foods’ as well, label them as such, and market them that way. They promise to ‘enhance mood’, ‘promote relaxation and good karma’, ‘increase alertness’, and ‘improve memory’ – all without scientific evidence to support such claims.

Chapter 13: The trace minerals

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FIGURE H13.1   An array of phytochemicals in a variety of foods and beverages

Broccoli and broccoli sprouts contain an abundance of the cancer-fighting phytochemical sulforaphane. Shutterstock.com/SOMMAI

An apple a day – rich in flavonoids – may protect against lung cancer. iStock.com/Roman Rybaleov

The phytoestrogens of soybeans seem to starve cancer cells and inhibit tumour growth; the phytosterols may lower blood cholesterol and protect cardiac arteries.

Garlic, with its abundant organosulphur compounds, may lower blood cholesterol and protect against stomach cancer. Shutterstock.com/Nataliia K

iStock.com/subjug

The ellagic acid of strawberries may inhibit certain types of cancer. The phytochemical resveratrol found in grapes (and nuts) protects against cancer by inhibiting cell growth and against heart disease by limiting clot formation and inflammation.

The flavonoids in black tea may protect against heart disease; those in green tea may defend against cancer.

Shutterstock.com/Hadescom

Shutterstock.com/nexus 7

The monoterpenes of citrus fruits (and cherries) may inhibit cancer growth.

Shutterstock.com/Africa Studio

iStock.com/sakdam

The flavonoids in cocoa and chocolate defend against oxidation and reduce the tendency of blood to clot. iStock.com/fcafotodigital

Tomatoes, with their abundant lycopene, may defend against cancer by protecting DNA from oxidative damage. PhotoDisc

Flaxseed, the richest source of lignans, may prevent the spread of cancer.

Blueberries, a rich source of flavonoids, improve memory in animals. Shutterstock.com/Diana Taliun

iStock.com/-slav-

Spinach and other colourful vegetables contain the carotenoids lutein and zeaxanthin, which help protect the eyes against macular degeneration. Shutterstock.com/Kolpakova Svetlana

Many processed foods become functional foods when they are fortified with nutrients or enhanced with phytochemicals or herbs (e.g. sterol-enriched margarines). Less frequently, an entirely new food is created, as in the case of a meat substitute (trade name Quorn) made of mycoprotein – a protein derived from a fungus. This functional food not only provides dietary fibre, polyunsaturated fats and high-quality protein, but it lowers LDL cholesterol, raises HDL cholesterol, improves glucose response and prolongs satiety after a meal. Such a novel functional food raises the question – is it a food or a drug?

Foods as pharmacy Not too long ago, most of us could agree on what was a food and what was a drug. Today, functional foods blur the distinctions. They have characteristics similar to both foods and drugs, but do not fit neatly into either category. The use of functional foods as drugs creates a whole new set of diet planning challenges. Not only must foods provide an adequate intake of all the nutrients to support good health, but they must also deliver drug-like ingredients to protect against diseases.

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Shutterstock.com/ denizya

TABLE H13.1   The colours of foods rich in phytochemicals Red – anthocyanins, lycopene Beets Cherries Cranberries Pink grapefruit

Pomegranates Radicchio Radishes Raspberries

Red apples Red peppers Red potatoes Rhubarb

Strawberries Tomatoes Watermelon

Dates Garlic Ginger

Leeks Mushrooms Onions

Parsnips Shallots Turnips

Persimmons Pineapple Pumpkin Rockmelon

Squash Sweet potatoes Tangerines Yellow peppers

Plums Purple figs Purple peppers

Raisins Purple cabbage Purple grapes

Green peppers Honeydew melon Kiwifruit Leafy greens Limes Okra Peas

Rocket Snow peas Spinach Sugar snap peas Watercress Zucchini

Shutterstock.com/ Elena Veselova

Shutterstock.com/ Africa Studio/

Alamy Stock Photo/D. Hurst

White–brown – allicin, allyl sulfides Bananas Brown pears Cauliflower Chives

Orange–yellow – beta-carotene, limonene Apricots Carrots Lemons Mangoes

Nectarines Oranges Papayas Peaches

Blue-purple – anthocyanins, ellagic acid, phenolics Black currants Blackberries Blueberries

Dried plums Eggplant Elderberries

Artichokes Asparagus Avocados Broccoli Brussels sprouts Cabbage Celery

Craig M. Moore

J. R. Bale/Alamy Stock Photo

Green – beta-carotene, lutein, indoles

Nature offers a variety of functional foods that provide us with many health benefits.

Like drugs used to treat chronic diseases, functional foods may need to be eaten several times a day for several months or years to have a beneficial effect. Sporadic users may be disappointed in the results. Margarine enriched

Cucumbers Endive Green apples Green beans Green grapes Green onions Green pears

with 2 to 3 grams of phytosterols may reduce cholesterol by up to 15 per cent, much more than regular margarine does, but not nearly as much as the more than 30 per cent reduction seen with statin cholesterol-lowering drugs. For this reason, functional foods may be more useful for prevention and mild cases of disease than for intervention and more severe cases. In any case, because prescription medicines are so much more effective and because people respond to plant sterols so differently, consumers should always make treatment decisions in consultation with their healthcare providers. Foods and drugs differ dramatically in cost as well. Functional foods, such as fruits and vegetables, incur no added costs, but foods that have been manufactured with added phytochemicals can be expensive, costing up to six times as much as their conventional counterparts – yet still below the costs of medicines.

Chapter 13: The trace minerals

In January 2016, FSANZ introduced new legislation regulating nutrition content claims and health claims on food labels and in advertisements.10 Health claims now fall into two categories. One is general-level health claims that refer to a nutrient or substance in a food and its effect on a general health function; for example, calcium is good for bones and teeth. The other category is high level health claims, which refer to a nutrient or substance in a food and its relationship to a serious disease or to a biomarker of a serious disease; for example, ‘Diets high in calcium may reduce the risk of osteoporosis in people 65 years and over’. An example of a biomarker health claim is, ‘Phytosterols may reduce blood cholesterol’. High-level health claims must be based on a food–health relationship pre-approved by FSANZ. There are currently 13 pre-approved food–health relationships for high-level health claims listed in the Standard.

Unanswered questions To achieve a desired health effect, which is the better choice: to eat a food designed to affect a body function or simply to adjust the diet? Does it make more sense to use a margarine enhanced with a phytosterol that lowers blood cholesterol or simply to limit the amount of butter eaten? Is it smarter to eat eggs enriched with omega-3 fatty acids or to restrict egg consumption? Might functional foods offer a sensible solution for improving health – if done correctly? Perhaps so, but the problem is that the food industry is moving faster than either scientists or the Therapeutic Goods Administration can keep up. Consumers were able to buy soup with St John’s wort that claimed to enhance mood, and fruit juice with echinacea that was supposed to fight colds, while scientists were still conducting their studies on these ingredients. Research to determine the safety and effectiveness of these and other substances is an ongoing process. Until this work is complete, consumers are on their own in finding the answers to the following questions: • Does it work? Research is generally lacking and findings are often inconclusive. • How much does it contain? Food labels are not required to list the quantities of added phytochemicals. Even if they were, consumers have no standard for comparison and cannot deduce whether the amounts listed are a little or a lot. Most importantly, until research is complete, food manufacturers do not know what amounts (if any) are most effective – or most toxic.

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• Is it safe? Functional foods can act like drugs. They contain ingredients that can alter body functions and cause allergies, drug interactions, drowsiness and other side effects. Yet, unlike drug labels, food labels do not provide instructions for the dosage, frequency or duration of treatment. • Is it healthy? Adding phytochemicals to a food does not magically make it a healthy choice. A chocolate bar may be fortified with phytochemicals, but it is still made mostly of sugar and fat. Critics suggest that the designation ‘functional foods’ may be nothing more than a marketing tool. After all, even the most experienced researchers cannot yet identify the perfect combination of nutrients and phytochemicals to support optimal health. Yet manufacturers are freely experimenting with various concoctions as if they possessed that knowledge. Is it okay for them to sprinkle phytochemicals on snack foods or confectionery and label them ‘functional’, thus implying health benefits?

Future foods Nature has elegantly designed foods to provide us with a complex array of dozens of nutrients and thousands of additional compounds that may benefit health – most of which we have yet to identify or understand. Over the years, we have taken those foods, deconstructed them and then reconstructed them in an effort to ‘improve’ them. With new scientific understandings of how nutrients – and the myriad other compounds in foods – interact with genes, we may some day be able to design foods to meet the exact health needs of each individual. Indeed, our knowledge of the human genome and of human nutrition may well merge to allow specific recommendations for individuals based on their predisposition to diet-related diseases. If the present trend continues, some day doctors or dietitians may be able to prescribe the perfect foods to enhance your health, and farmers will be able to grow them. As Highlight 19 explains, scientists have already developed gene technology to alter the composition of food crops. They can grow rice enriched with vitamin A and tomatoes containing a hepatitis vaccine, for example. It seems quite likely that foods can be created to meet every possible human need. But then, the bounty of nature has long provided human beings with a variety of foods to meet our needs.

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HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1

Which do you believe is the better choice: eating highly processed foods that have been enhanced with phytochemicals that show evidence for a health benefit, or choosing foods that are minimally processed, close to their natural state and rich in phytochemicals?

2

Limited research suggests that foods rich in phytoestrogens may benefit heart, bone, breast and

menopausal health, but phytoestrogen supplements or phytoestrogen-enhanced functional foods are not recommended, particularly for women at high risk of breast cancer. How can you determine whether a phytochemical and/or functional food offers a safe and sensible solution to improving your health?

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search ‘functional foods’ at the International Food Information Council Foundation website: http://www. foodinsight.org

• •

Search ‘functional foods’ at the Dietitians Australia site: http://www.dietitiansaustralia.org.au Find out if warnings have been issued for any food ingredients at the TGA website: http://www.tga.gov.au

REFERENCES CHAPTER 1

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Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). B. Qi and M. Han, Microbial siderophore enterobactin promotes mitochondrial iron uptake and development of the host via interaction with ATP synthase, Cell 175 (2018): P571–582. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). G. Rishi and V. N. Subramaniam, Signaling pathways regulating hepcidin, Vitamins and Hormones 110 (2019): 47–70. World Health Organization, Anaemia https://www.who.int/healthtopics/anaemia, accessed 27 February 2021. E. Sal and co-authors, Relationship between obesity and iron deficiency anemia: Is there a role of hepcidin? Hematology 23 (2018): 542–548. C. Borgna-Pignatti and S. Zanella, Pica as a manifestation of iron deficiency, Expert Reviews of Hematology 9 (2016): 1075–1080.

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K. V. Kowdley and co-authors, ACG clinical guideline: Hereditary hemochromatosis, American Journal of Gastroenterology 114 (2019): 1202–1218. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). H. Hemilä, Zinc lozenges and the common cold: A meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage, JSRM Open 8 (2017). K. Charlton, Y. Probst and G. Kane, Dietary iodine intake of the Australian population after introduction of a mandatory iodine fortification programme, Nutrients 8 (2016): 701. B. G. Biban and C. Lichiardopol, Iodine deficiency, still a global problem? Current Health Sciences Journal 43 (2017): 103–111. M. Vinceti and co-authors, Selenium for preventing cancer, Cochrane Database of Systematic Reviews (2018): CD005195. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006).

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Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006).

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R. B. Costello, J. T. Dwyer, and R. L. Bailey, Chromium supplements for glycemic control in type 2 diabetes: Limited evidence of effectiveness, Nutrition Reviews 74 (2016): 455–468.

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C. H. Pernar and co-authors, The epidemiology of prostate cancer, Cold Spring Harbor Perspectives in Medicine 8 (2018): a030361. World Cancer Research Fund/American Institute for Cancer Research, Diet, Nutrition, Physical Activity and Cancer: a Global Perspective, Continuous Update Project Expert Report 2018. F. Perez-Vizcaino and C. G. Fraga, Research trends in flavonoids and health, Archives in Biochemistry and Biophysics 646 (2018): 107–112. E. A. Trautwein and co-authors, LDL-cholesterol lowering of plant sterols and stanols: Which factors influence their efficacy? Nutrients 10 (2018): E1262. Food Standards Australia New Zealand, Nutrition content claims and health claims (2016), http://www.foodstandards.gov.au/consumer/ labelling/nutrition

HIGHLIGHT 1

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4 5

A. Ranjan and co-authors, Role of phytochemicals in cancer prevention, International Journal of Molecular Sciences 20 (2019): E4981. M. Messina, Soy and health update: Evaluation of the clinical and epidemiologic literature, Nutrients 8 (2016): E754. I. Sahin and co-authors, Soy isoflavones in integrative oncology: Increased efficacy and decreased toxicity of cancer therapy, Integrative Cancer Therapies 18 (2019). S. Ziaei and R. Halaby, Dietary isoflavones and breast cancer risk, Medicines 4 (2017): E18. Cancer Council Australia, Position statement - Soy, phyto-estrogens and cancer prevention. Available at https://wiki.cancer.org.au/policy/ Position_statement_-_Soy,_phyto-oestrogens_and_cancer_prevention

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14

FITNESS: PHYSICAL ACTIVITY, NUTRIENTS AND BODY ADAPTATIONS Nutrition in your life

Every day, you choose to be physically active or not. Over time, these choices will influence how well you feel and how long you live. Today’s world makes it easy to be inactive – too easy, in fact – but the many health rewards of being physically active make it well worth the effort. You may even discover how much fun it is to be active, and, with a little perseverance, you may become physically fit as well. The choice is yours. As you read this chapter, consider whether your physical activities meet current recommendations and whether your daily food, fluid, and nutrient intakes are appropriate to support those activities. P UTTING COMMON SENSE TO THE TEST Circle your answer

T

F Regular exercise can reduce the risk of developing some types of cancers.

T

F Creatine phosphate is a reliable energy reserve for distance runners.

T

F As exercise intensity increases, glycogen utilisation also increases.

T

F Protein needs for endurance athletes are the same as those of sedentary people.

T

F Male bodybuilders are the most ‘at risk’ group for iron deficiency.

LEARNING OBJECTIVES 14.1 Describe the health benefits of being physically fit and explain how to develop the components of fitness.

14.2 Identify the factors that influence fuel use during physical activity and the types of activities that depend more on glucose or fat, respectively.

Unlike many other fruits that are high in carbohydrates, coconuts provide mostly fat

Chapter 14: Fitness: physical activity, nutrients and body adaptations

14.3 List which vitamin and mineral supplements, if any, athletes may need and why. 14.4 Identify the factors that influence an athlete’s fluid needs and describe the differences between water and sports drinks.

14.5 Describe a daily eating pattern that is appropriate for an athlete and provide an example of a recommended pre-game meal and also a recommended recovery meal. 14.6 Present arguments for and against the use of ergogenic aids.

Are you physically fit? If so, the following description applies to you. Your joints are flexible, your muscles are strong and your body is lean with enough, but not too much, fat. You have the endurance to engage in daily physical activities with enough reserve energy to handle added challenges. Carrying heavy suitcases, opening a stuck window or climbing four flights of stairs, which might strain an unfit person, are easy for you. What’s more, you are prepared to meet mental and emotional challenges, too. All these characteristics of fitness describe the same wonderful condition of a healthy body. Alternatively, you may be mostly sedentary. Today’s world encourages inactivity, and people who exert minimal physical effort can become weak and unhealthy. In fact, a sedentary lifestyle contributes to the development of several chronic diseases. This chapter is written for you, whoever you are and whatever your goals – whether you want to improve your health, lose weight, hone your athletic skills, or simply adopt an active lifestyle. It begins by describing fitness and its benefits and then explains how the body uses energy nutrients to fuel physical activity. Finally, it describes diets to support fitness.

14.1 Fitness

Fitness depends on a certain minimum amount of physical activity or exercise. Both physical activity and exercise involve body movement, muscle contraction and enhanced energy expenditure, but ‘exercise’ is often used to describe structured, planned physical activity. This chapter focuses on how the active body uses energy nutrients – whether that body is pedalling a bike across campus or pedalling a stationary bike in a gym. Thus, for our purposes, the terms physical activity and exercise are used interchangeably.

Benefits of fitness The health benefits of increasing physical activities and reducing sedentary times cannot be overemphasised. Extensive evidence confirms that regular physical activity promotes health and reduces the risk of developing a number of diseases.1 Yet, despite an increasing awareness of the health benefits that physical activity confers, the Australian National Health Survey showed that only 55 per cent of adults aged 18 to 64 exercised sufficiently to meet a minimum goal of 150 minutes of activity each week, and in New Zealand the figure is similar, at 52 per cent.2 Like smoking and obesity, physical inactivity is linked to the major degenerative diseases – heart disease, cancer, stroke, diabetes and hypertension – the primary killers of adults in developed countries. As a person becomes physically fit, the health of the entire body improves. In general, physically fit people enjoy: • Restful sleep – rest and sleep occur naturally after periods of physical activity. During rest, the body repairs injuries, disposes of wastes generated during activity and builds new physical structures. • Nutritional health – physical activity expends energy and thus allows people to eat more food. If they choose wisely, active people will consume more nutrients and be less likely to develop nutrient deficiencies.

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PUTTING COMMON SENSE TO THE TEST

Regular exercise can reduce the risk of developing some types of cancers. TRUE

• Improved body composition – a balanced program of physical activity limits body fat and increases or maintains lean tissue. Physically active people have relatively less body fat than sedentary people at the same body weight. • Improved bone density – weight-bearing physical activity builds bone strength and protects against osteoporosis. • Resistance to colds and other infectious diseases – fitness enhances immunity. • Low risks of some cancers – lifelong physical activity may help to protect against colon cancer, breast cancer and some other cancers. • Strong circulation and lung function – physical activity challenges the heart and lungs and strengthens the circulatory system. • Low risk of cardiovascular disease – physical activity lowers blood pressure, slows resting heart rate and lowers blood cholesterol, thus reducing the risks of heart attacks and strokes. • Low risk of type 2 diabetes – physical activity normalises glucose tolerance and reduces the risk of developing type 2 diabetes. • Reduced risk of gall bladder disease – regular physical activity reduces the risk of gall bladder disease – perhaps by facilitating weight control and lowering blood lipid levels. • Low incidence and severity of anxiety and depression – physical activity may improve mood and enhance the quality of life by reducing depression and anxiety. • Strong self-image – the sense of achievement that comes from meeting physical challenges promotes self-confidence. • Long life and high quality of life in the later years – active people live longer healthier lives than sedentary people do. In addition to extending longevity, physical activity supports independence and mobility in later life by reducing the risk of falls and minimising the risk of injury should a fall occur.

Physical activity benefits revealed The health benefits of regular physical activity have long been known, but the mechanisms underlying such benefits have, until recently, been difficult to elucidate. As discussed above, regular physical activity may protect against major chronic diseases by positively influencing metabolic risk factors, such as obesity, high blood pressure, insulin resistance, inflammation, and blood lipids. Exactly how physical activity may exert such widespread improvements to health has recently begun to be revealed and involves thousands of metabolic processes and pathways. As discussed in Chapter 5, adipose tissue actively secretes proteins known as adipokines that help regulate energy balance and other body functions and in turn influence health. Similarly, researchers now know that during or immediately after physical activity, skeletal muscles release proteins known as myokines and that over time, these myokines elicit systemic changes.3 Myokines released by skeletal muscle during physical activity evoke changes in skeletal muscle as well as in adipose tissue and organs, such as the liver. For example, one myokine is thought to have an anti-inflammatory effect and counteract insulin resistance. The identification and function of skeletal muscle myokines requires much more research, but the limited evidence thus far provides promise for a greater understanding of the relationships between regular physical activity and adaptive changes that enhance health and protect against chronic diseases.

Physical activity guidelines What does a person have to do to reap the health rewards of physical activity? Australia’s Physical Activity and Sedentary Behaviour Guidelines for Adults specify that being physically active and limiting sedentary behaviour every day is essential for health and wellbeing.4 These guidelines are closely mirrored in almost identical recommendations for New Zealand adults.5 The national physical activity guidelines for adults (aged 18–64) comprise a four-tier series of recommendations:

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• Doing any physical activity is better than doing none. If you currently do no physical activity, start by doing some, and gradually build up to the recommended amount. • Be active on most, preferably all, days every week. • Accumulate 150 to 300 minutes (2½ to 5 hours) of moderateintensity physical activity or 75 to 150 minutes (1¼ to 2½ hours) of vigorous intensity physical activity, or an equivalent combination of both moderate and vigorous activities, each week. • Do muscle strengthening activities on at least two days each week. In addition to the physical activity guidelines, there are also sedentary behaviour guidelines: Physical activity, or its lack, exerts a significant and • Minimise the amount of time spent in prolonged sitting. pervasive influence on everyone’s nutrition and overall • Break up long periods of sitting as often as possible. health. In addition to providing health benefits, physical activity helps to develop and maintain fitness. Table 14.1 presents the American College of Sports Medicine (ACSM) guidelines for physical activity.6 The ACSM guidelines can be used Reminder: Body in conjunction with the Australian guidelines as they both have similar goals of helping to composition refers to ensure sufficient activity for health benefits that cover aerobic, strength and flexibility areas. the proportions of Following these guidelines will help adults improve their cardiorespiratory endurance, body muscle, bone, fat and composition, strength and flexibility. At this level of fitness, a person can reap still greater other tissue that make health benefits; for example, a substantially lower risk of premature death compared with up a person’s total those who are inactive, improved cardiorespiratory fitness and improved body composition. body weight.

David Hanover Photography

David Hanover Photography

David Hanover Photography

TABLE 14.1   Guidelines for physical fitness

Type of activity

Aerobic activity that uses largemuscle groups and can be maintained continuously

Resistance activity that is performed at a controlled speed and through a full range of motion

Stretching activity that uses the major muscle groups

Frequency

Five to seven days per week

Two to three days per week

Two to seven days per week

Intensity

Moderate (equivalent to walking at a pace of 5 to 6 kilometres per hour)a

Enough to enhance muscle strength and improve body composition

Enough to feel tightness or slight discomfort

Duration

At least 30 minutes per day

2 to 4 sets of 8 to 12 repetitions involving each major muscle group

2 to 4 repetitions of 15 to 30 seconds per muscle group

Examples

Running, cycling, swimming, in-line skating, aerobic classes, rowing, power walking, kickboxing, skipping; sports activities, such as football, rugby, basketball, netball, soccer, squash, tennis, volleyball

Pull-ups, push-ups, weightlifting, Pilates

Yoga

a For those who prefer vigorous-intensity aerobic activity, such as walking at a very brisk pace (>6 km/h) or running (>8 km/h), a minimum of 20 minutes per day, three days per week is recommended.

Adapted from American College of Sports Medicine position stand: Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults – guidance for prescribing exercise, Medicine and Science in Sports and Exercise 43 (2011): 1334–1359.

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The bottom line is that any physical activity, even moderate activity, beyond activities of daily living, provides some health benefits, and these benefits follow a dose–response relationship. In other words, some activity is better than none, and more activity is better still – up to a point. Pursued in excess, intense physical activity, especially when combined with poor eating habits, can undermine health, as Highlight 8 explains.

Developing fitness A person who practises a physical activity adapts by becoming better able to perform that activity after each session. People shape their bodies by what they choose to do. Muscle cells and tissues respond to a physical activity overload by building, within genetic limits, the structures needed to perform it. Muscles are continuously under renovation. Every day, particularly during the fasting periods between meals, a healthy body degrades a small portion of its muscle protein and then rebuilds new muscle with available amino acids during feeding periods. This balance between protein degradation and synthesis maintains the body’s muscle tissue. To gain muscle tissue, protein synthesis must be greater than degradation, a condition called hypertrophy. When protein degradation is greater than synthesis, the result is atrophy. Physical activity tips the balance toward muscle hypertrophy. The opposite is also true: unused muscles diminish in size and weaken over time, tipping the balance towards muscle atrophy. The muscles adapt and build only the proteins they need to cope with the work performed. Muscles engaged in activities that require strength develop more of the proteins needed for greater muscle mass, as evidenced by the fact that body builders have large, well-developed muscles. By comparison, those engaged in endurance activities develop more of the proteins needed to combat muscle fatigue; distance cyclists can pedal for many hours before fatigue sets in.

Strategies to build fitness and prevent injuries

Major coronary risk factors are: • age (men ≥45 years or women ≥55 years) • family history of heart disease • cigarette smoking • hypertension • serum cholesterol >5.5 mmol/L or HDL 30 kg/m2).

A variety of physical activities produces the best overall fitness and, to this end, people need to work different muscle groups from day to day. This strategy provides a day or two of rest for different muscle groups, giving them time to replenish nutrients and to repair any minor damage incurred by the activity. Other tips for building fitness and minimising the risk of overuse injuries are as follows: • Be active all week, not just on the weekends. • Use proper equipment and wear proper attire. • Perform exercises using proper form. • Include warm-up and cool-down activities in each session. Warming up helps to prepare muscles, ligaments and tendons for the upcoming activity and mobilises fuels to support strength and endurance activities. Cooling down reduces muscle cramping and allows the heart rate to slow gradually. • Train hard enough to challenge your strength or endurance a few times each week rather than every time you work out. Between challenges, do moderate workouts. Also, include at least one day of rest each week. • Pay attention to body signals. Symptoms such as abnormal heartbeats, dizziness, lightheadedness, cold sweat, confusion or pain or pressure in the middle of the chest, teeth, jaw, neck or arm demand immediate medical attention. • Work out wisely. Do not start with activities so demanding that pain stops you within a day or two. Learn to enjoy small steps towards improvement. Fitness builds slowly.

Cautions on starting a fitness program Before beginning a fitness program, make sure it is safe for you to do so. Most apparently healthy people can begin a moderate exercise program, such as walking or increasing daily activities, without a medical examination, but people with known major coronary risk factors or metabolic or kidney disease may need health screening and exercise testing to minimise the risks of adverse exercise-related cardiovascular events.

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To be physically fit, a person must develop enough flexibility, muscle strength and endurance, and cardiorespiratory endurance to meet the everyday demands of life with some to spare, and to achieve a reasonable body weight and body composition. Flexibility allows the joints to move freely, reducing the risk of injury. Cardiorespiratory endurance supports the ongoing activity of the heart and lungs. Muscle strength and muscle endurance enable muscles to work harder and longer without fatigue. Body composition improves as physical activity supports lean body tissues and reduces excess body fat. Although nutrition influences each component of fitness to some extent, its role in flexibility is not as apparent as for the others. For this reason, cardiorespiratory endurance and muscle strength and endurance are emphasised in the following sections. As the heart and lungs improve their capacity to sustain physical activity and the muscles become stronger and less readily fatigued, body composition improves – body fat decreases and lean body mass increases. Chapter 8 discusses body composition and the health risks of too much body fat.

Cardiorespiratory endurance

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The length of time a person can remain active with an elevated heart rate – that is, the ability of the heart, lungs and blood to sustain Physical activity helps you look good, feel good a given demand – defines a person’s cardiorespiratory endurance. and have fun, and it brings many long-term health benefits as well. Cardiorespiratory endurance training improves a person’s ability to sustain vigorous activities, such as running, brisk walking or swimming. Such training enhances the capacity of the heart, lungs and blood to deliver Recall from oxygen to, and remove waste from, the body’s cells. Cardiorespiratory endurance training, Chapter 7 that therefore, is aerobic. As the cardiorespiratory system gradually adapts to the demands aerobic means of aerobic activity, the body delivers oxygen more efficiently. In fact, the accepted measure requiring oxygen. of a person’s cardiorespiratory fitness is maximal oxygen uptake (VO2max). The benefits of cardiorespiratory training are not just physical, though, because all of the body’s cells, including the brain cells, require oxygen to function. When the cells receive more oxygen more readily, both the body and the mind benefit.

People’s bodies are shaped by the activities they perform.

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The components of fitness

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Cardiorespiratory endurance reflects the health of the heart and circulatory system, on which all other body systems depend. Figure 14.1 shows the major relationships between the heart, circulatory system and lungs. To improve cardiorespiratory endurance, activities must be sustained for 20 minutes or longer and use most of the large-muscle groups of the body (legs, buttocks, and abdomen). The level of training must be intense enough to elevate heart rate. A person’s own perceived effort is usually a reliable indicator of the intensity of an activity. In general, workouts should be at an intensity that raises your heart rate but still leaves you able to talk comfortably. For those who are more competitive and want to work to their limits on some days, a treadmill test can reveal the maximum heart rate. Workouts are safe at up to 85 per cent of that rate.

FIGURE 14.1   Delivery of oxygen by the heart and lungs to the muscles The cardiorespiratory system responds to the muscles’ demand for oxygen by building up its capacity to deliver oxygen. Researchers can measure cardiorespiratory fitness by measuring the maximum amount of oxygen a person consumes per minute while working out, a measure called VO2max.

1 The respiratory system delivers oxygen to the blood.

Air (O2, CO2), other gases O2

CO2

CO2

CO2 O2

O2

4 The blood carries the carbon dioxide back to the lungs.

CO2

2 The circulatory system carries oxygenated blood throughout the body.

O2

3 The muscles and other tissues obtain oxygen from the blood and release carbon dioxide into it.

Chapter 14: Fitness: physical activity, nutrients and body adaptations

Cardiorespiratory conditioning

Cardiorespiratory conditioning occurs as aerobic workouts improve heart and lung activities. Cardiac output increases, thus enhancing oxygen delivery. The heart becomes stronger, and each beat pumps more blood. Because the heart pumps more blood with each beat, fewer beats are necessary, and the resting heart rate slows down. The average resting pulse rate for adults is around 70 beats per minute, but people who achieve cardiorespiratory conditioning may have resting pulse rates of 50 or even lower. The muscles that work the lungs become stronger, too, so breathing becomes more efficient. Circulation through the arteries and veins improves. Blood moves easily, and blood pressure declines.7 Table 14.1 includes the ACSM guidelines for developing and maintaining cardiorespiratory fitness.

Muscle conditioning One of the benefits of cardiorespiratory training is that fit muscles use oxygen efficiently, reducing the heart’s workload. An added bonus is that muscles that use oxygen efficiently can burn fat longer during activity – a plus for body composition and weight control.

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Cardiorespiratory conditioning: • increases cardiac output and oxygen delivery • increases blood volume per heartbeat (stroke volume) • slows resting heart rate • increases breathing efficiency • improves circulation • reduces blood pressure.

Muscle strength and endurance Resistance training has long been recognised as a means to build lean body mass and develop and maintain muscle strength and endurance. Additional benefits of resistance training, however, have emerged only recently. Progressive resistance training not only increases muscle strength and endurance, but it also prevents and manages several chronic diseases, including cardiovascular disease, and enhances psychological wellbeing.8 Resistance training can also help to maximise and maintain bone mass. Even in women past menopause (when most women are losing bone), resistance training can improve bone density. By strengthening muscles in the back and abdomen, resistance training can improve posture and reduce the risk of back injury. Resistance training can also help prevent the decline in physical mobility that often accompanies ageing.9 Older adults, even those in their eighties, who participate in resistance training programs gain both muscle strength and muscle endurance, which enables them to walk longer before exhaustion. Leg strength and walking endurance are powerful indicators of an older adult’s physical abilities. Resistance training builds muscle strength, muscle power and muscle endurance. To emphasise muscle strength, combine high resistance (heavy weight) with a low number of repetitions (8–10).10 To emphasise muscle endurance, combine less resistance (lighter weight) with more repetitions (12–15). Resistance training enhances performance in other sports, too. Swimmers can develop a more efficient stroke and tennis players a more powerful serve when they train with weights, for example.

AUSTRALIAN DIETARY GUIDELINES 2013 ---------------

To achieve and maintain a healthy weight, be physically active and choose amounts of nutritious food and drinks to meet your energy needs.

The intensities and types of physical activities that are best for one person may not be good for another. A person who has been sedentary will initially perform at a dramatically different level of intensity than a fit person. The type of physical activity that is best for you depends, too, on what you want to achieve and what you enjoy doing. Some people love walking, whereas others prefer to dance or ride a bike. Those who want to be stronger and firmer will lift weights. Keep in mind that muscle is more metabolically active than body fat, so the more muscle you have, the more energy you’ll expend. In a balanced fitness program, aerobic activity improves cardiorespiratory fitness, stretching enhances flexibility, and resistance

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A balanced fitness program

The key to regular physical activity is finding an activity that you enjoy.

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training develops muscle strength, muscle power and muscle endurance. Table 14.2 provides an example of a balanced fitness program. Chapter 17 presents a discussion of physical activity for older adults.

TABLE 14.2   A sample balanced fitness program Monday, Tuesday, Wednesday, Thursday, Friday: • 5 minutes of warm-up activity • 30–60 minutes of aerobic activity • 10 minutes of cool-down activity and stretching Tuesday, Thursday, Saturday: • 5 minutes of warm-up activity • 30 minutes of resistance training • 10 minutes of cool-down activity and stretching Saturday and/or Sunday: • Sports, walking, hiking, biking or swimming

REVIEW IT

Physical activity brings good health and long life. To develop fitness – whose components are flexibility, cardiorespiratory endurance, muscle strength and endurance, and body composition – a person must condition the body, through training, to adapt to the activity performed.

14.2  Energy systems and fuels to support activity

Nutrition and physical activity go hand in hand. Activity demands carbohydrate and fat as fuel, protein to build and maintain lean tissues, vitamins and minerals to support both energy metabolism and tissue building, and water to help distribute the fuels and to dissipate the resulting heat and wastes. This section describes how nutrition supports a person who decides to get up and go.

The energy systems of physical activity

Recall from Chapter 7 that anaerobic means not requiring oxygen.

PUTTING COMMON SENSE TO THE TEST

Creatine phosphate is a reliable energy reserve for distance runners. FALSE

As Chapter 7 describes, the high-energy compound ATP provides the energy that powers all the activities of living cells. ATP is present in small amounts in all body tissues all the time, and it can deliver energy instantly. Muscle cells may need additional ATP to power their many activities. When an ATP molecule is split in the muscle cells, the energy released contracts muscles and generates heat. Thus, physical exertion uses ATP. The three major energy systems described next enable muscle cells to regenerate ATP during different types of physical activity: • the phosphagen system (also called the creatine phosphate system) • the lactic acid system (anaerobic glycolysis) • the aerobic system (aerobic glycolysis, fatty acid oxidation, and TCA cycle). All three energy systems function at all times, but depending on the intensity of the activity and the conditioning of the athlete, one system will predominate at any given time. The following sections describe each of these systems.

The phosphagen system Immediately after the onset of a demand, before muscle ATP pools dwindle, a muscle enzyme begins to break down another high-energy compound that is stored in the muscle: CP, or creatine phosphate. CP is made from creatine, a compound commonly found in muscles, with a phosphate group attached. CP can split anaerobically to release phosphate which can be used to replenish ATP. Supplies of CP in a muscle last for only about 10 seconds, producing enough quick energy without oxygen for a 100-metre sprint.

Chapter 14: Fitness: physical activity, nutrients and body adaptations

When activity ceases and the muscles are resting, ATP gives up one of its phosphate groups to creatine. Thus, CP is produced during rest by reversing the process that occurs during muscular activity. Highlight 14 includes creatine supplements in its discussion of substances commonly used in the pursuit of fitness.

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During rest: • ATP + creatine → CP. During activity: • CP → ATP + creatine.

The lactic acid system After the first 10 seconds or so of intense activity, energy from the phosphagen system diminishes, and muscle cells call upon the lactic acid system to produce more ATP. As Chapter 7 describes, the lactic acid system involves the anaerobic breakdown of glucose to pyruvate (and then of pyruvate to lactate). The primary source of glucose is muscle glycogen. This system can generate a small amount of ATP quickly for high-intensity activity lasting up to three minutes. A later section describes the consequences of lactate accumulation.

The aerobic system To meet the more prolonged demands of sustained activity, the muscles rely on the aerobic system to provide ATP for muscle contraction. As Chapter 7 describes, carbohydrate, fat and some amino acids are continuously oxidised to ensure an uninterrupted supply of ATP. During rest, the body derives more than half of its ATP from the oxidation of fatty acids, the majority of any other ATP comes from the complete oxidation of glucose, and a small percentage from the oxidation of amino acids. During physical activity, the body adjusts its mixture of fuels. Muscles always use a mixture of fuels – never just one. How much of which fuel the muscles use during physical activity depends on an interplay among the fuels available from the diet, the intensity and duration of the activity, and the degree to which the body is conditioned to perform that activity. The next sections explain these relationships by examining each of the energy-yielding nutrients individually, but keep in mind that, although one fuel may predominate at a given time, the other two will still be involved. Table 14.3 shows how fuel use changes according to the intensity and duration of the activity.

TABLE 14.3 ACTIVITY INTENSITY

Primary fuels used for activities of different intensities and durations ACTIVITY DURATION

ENERGY SYSTEM

PREFERRED FUEL SOURCE

OXYGEN NEEDED?

ACTIVITY EXAMPLE

Extreme

5 to 10 sec

Phosphagen system

ATP-CP (immediate availability)

No

100-metre sprint, shot put, golf or baseball bat swing, tennis or volleyball serve

Very high

20 sec to 2 min

Lactic acid system

ATP from carbohydrate (anaerobic glycolysis)

No

400-metre run, 100-metre swim, gymnastic routines

High

2 min to 20 min

Aerobic system

ATP from carbohydrate (glycolysis and TCA cycle)

Yes

Cycling, swimming, running

Moderate

>20 min

Aerobic system

ATP from fat (fatty acidoxidation and TCA cycle)

Yes

Hiking

Note: All energy systems function at all times, but depending on the intensity of the activity and the conditioning of the athlete, one system will predominate at any given time.

Anaerobic versus aerobic Central to the energy systems just described is oxygen – or lack of it. The phosphagen and lactic acid systems are anaerobic – meaning without oxygen. As its name suggests, the aerobic system uses oxygen. As you read the following pages, notice how the fuel mixture shifts depending on whether the activity is anaerobic or aerobic. Anaerobic activities are associated with strength, agility, and split-second surges of power. The jump of a slam dunk, the power of a tennis serve and the heave of a bench press all involve anaerobic work. Such high-intensity, short-duration activities depend mostly on glucose as the chief energy fuel in the lactic acid system.

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Endurance activities of low to moderate intensity and long duration depend more on fat to provide energy through the aerobic system. The ability to continue swimming to the shore, to keep on hiking to the top of the mountain, or to continue pedalling all the way home reflects aerobic capacity. As mentioned earlier, aerobic capacity is also crucial to maintaining a healthy heart and circulatory system. Because various physical activities use different energy systems and quantities of nutrients to various degrees, a person’s food choices can greatly influence performance.

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Glucose use during physical activity Glucose, stored in the liver and muscles as glycogen, is vital to physical activity. During exertion, the liver breaks down its glycogen and releases the glucose into the bloodstream. The muscles use this glucose as well as their own private glycogen stores to fuel their work. Glycogen supplies can easily support everyday activities but are limited to less than 8000 kilojoules of energy, enough for about 40 kilometres of running. The more glycogen the muscles store, the longer the glycogen will last during physical activity, which in turn influences performance. When glycogen is depleted, the muscles become fatigued.

Sustained muscular efforts, as in a long-distance rowing event or a cross-country run, involve aerobic work.

Diet affects glycogen storage and use

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How much carbohydrate a person eats influences how much glycogen is stored. A classic study compared fuel use during activity between three groups of runners on different diets.11 For several days before testing, one group consumed a normal mixed diet, a second group consumed a high-carbohydrate diet and the third group consumed a no-carbohydrate diet (just fat and protein). As Figure 14.2 shows, the high-carbohydrate diet allowed the runners to keep going longer before becoming exhausted. This study and many others that followed have confirmed that high-carbohydrate diets enhance endurance by ensuring ample glycogen stores.

FIGURE 14.2   The effect of diet on physical endurance A high-carbohydrate diet can increase an athlete’s endurance. In the study described in the text, the fat and protein diet provided 94 per cent of energy from fat and 6 per cent from protein; the normal mixed diet provided 55 per cent of energy from carbohydrate; and the high-carbohydrate diet provided 83 per cent of energy from carbohydrate.

Split-second surges of power, as in the heave of a barbell or a jump of a basketball player, involve anaerobic work.

Maximum endurance time:

To fill glycogen stores, eat plenty of carbohydrate-rich foods.

Fat and protein diet

Getty Images/Jupiter Images

57 min Normal mixed diet 114 min High-carbohydrate diet 167 min

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Intensity of activity affects glycogen use How long an exercising person’s glycogen will last depends not only on diet but also on the intensity of the activity. Moderate activities, such as jogging, during which breathing is steady and easy, use glycogen slowly. The lungs and circulatory system have no trouble keeping up with the muscles’ need for oxygen. The individual breathes easily, and the heart beats steadily – the activity is aerobic. The muscles derive their energy from both glucose and fatty acids. By depending partly on fatty acids, moderate aerobic activity conserves glycogen. Intense activities – the kind that make it difficult ‘to catch your breath’, such as a 400-metre race – use glycogen quickly. In such activities, the muscles rely on the lactic acid system to break down glucose to pyruvate anaerobically, producing ATP quickly.

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PUTTING COMMON SENSE TO THE TEST

As exercise intensity increases, glycogen utilisation also increases. TRUE

Lactate Lactate is the product of anaerobic glycolysis. When the rate of glycolysis exceeds the capacity of the mitochondria to accept hydrogens with their electrons for the electron transport chain, the accumulating pyruvate molecules are converted to lactate. At low intensities, lactate is readily cleared from the blood, but at higher intensities, lactate accumulates. When the rate of lactate production exceeds the rate of clearance, intense activity can be maintained for only one to three minutes (as in a 400- to 800-metre race or a boxing match). Lactate was long blamed for muscle fatigue, but recent research disputes this idea. Working muscles may produce lactate and experience fatigue, but the lactate does not cause the fatigue.12 In contrast, depletion of muscle glycogen by about 80 per cent consistently produces fatigue. Lactate quickly leaves the muscles and travels in the blood to the liver. There, liver enzymes convert the lactate back into glucose. Glucose can then return to the muscles to fuel additional activity. (The recycling process that regenerates glucose from lactate is known as the Cori cycle, and is shown in Figure 7.7 in Section 7.2, Chapter 7.)

Glycogen use depends not only on the intensity of an activity but also on its duration. Initially, a person uses mostly glycogen for fuel. As the muscles devour their own glycogen, they become ravenous for more glucose. Glucagon signals the liver to empty out its glycogen stores to provide the muscles with more glucose. A person who continues exercising moderately (mostly aerobically) adapts over time to use less and less glycogen and more and more fat for fuel (review Table 14.3). Still, glucose use continues, and if the activity lasts long enough and is intense enough, blood glucose declines and muscle and liver glycogen stores are depleted. Physical activity can continue for a short time thereafter only because glucagon signals the liver to produce, from lactate and certain amino acids, the minimum amount of glucose needed to briefly forestall total depletion.

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Duration of activity affects glycogen use

Moderate- to high-intensity aerobic exercises that can be sustained for only a short time (less than 20 minutes) use some fat but more glucose for fuel.

Training affects glycogen use Training, too, affects how much glycogen muscles will store. Muscle cells that repeatedly deplete their glycogen through hard work adapt to store greater amounts of glycogen to support that work. Conditioned muscles also rely less on glycogen and more on fat for energy, so glycogen breakdown and glucose use occur more slowly in trained than in untrained individuals at a given work intensity. A person attempting an activity for the first time uses much more glucose

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The mitochondria are the structures within a cell responsible for producing ATP (see Figure 7.1 in Section 7.1, Chapter 7).

For perspective, snack ideas providing 60 g carbohydrate are: • 600 mL sports drink and a bread roll • 600 mL milk and four Anzac or oatmeal biscuits • 300 mL apple juice and a muesli bar.

than an athlete who is trained to perform it. Oxygen delivery to the muscles by the heart and lungs plays a role, but equally importantly, trained muscles are better equipped to use the oxygen because their cells contain more mitochondria. Untrained muscles depend more heavily on anaerobic glucose breakdown, even when physical activity is just moderate. Gluconeogenesis could support an activity of low intensity, such as walking, but cannot support continued strenuous activity. After a couple of hours of strenuous activity, glucose stores are depleted. When depletion occurs, it brings nervous system function to a near halt, making continued exertion at the same intensity almost impossible. Marathon runners refer to this point of glucose exhaustion as ‘hitting the wall’. To avoid such debilitation, endurance athletes try to maintain their blood glucose for as long as they can. The following guidelines will help endurance athletes maximise glucose supply: • Eat a high-carbohydrate diet (approximately 8 g of carbohydrate per kg of body weight, or about 70 per cent of energy intake) regularly. • Take glucose (usually in sports drinks) periodically during activities that last for 60 minutes or more. • Eat carbohydrate-rich foods (approximately 60 g of carbohydrate) immediately following activity.

Glucose before activity Most of an athlete’s glucose is provided by carbohydrate-rich meals consumed throughout the day. In addition, glucose consumed within a few hours before training or competition is thought to ‘top off’ the athlete’s glycogen stores, providing the greatest possible glucose supply to support sustained activity. The pre-game meal to provide glucose can take many forms, as a later section describes.

Glucose during activity

A later section discusses fluid and electrolyte balance during activity.

Muscles can obtain the glucose they need not only from glycogen stores, but also from foods and beverages consumed during activity. Consuming carbohydrate is especially useful during exhausting endurance activities (lasting more than 1 hour) and during games such as soccer or hockey, which last for hours and demand repeated bursts of intense activity. Interestingly, during high-intensity activity lasting less than an hour, some research suggests that merely rinsing the mouth with a carbohydrate solution may be enough to improve performance.13 Researchers speculate that there may be receptors in the mouth that sense potential carbohydrate availability and relay this message to areas of the brain involved with reward and motor control. Endurance athletes often run short of glucose by the end of competitive events. To ensure optimal carbohydrate intake, sports nutrition experts recommend 30 to 60 grams of carbohydrate per hour during prolonged events.14 Carbohydrate-based sports drinks offer a convenient way to meet this recommendation and also help replace water and electrolyte losses. Thus, to ensure optimal hydration and carbohydrate intake, endurance athletes are advised to drink one-half to one litre of a 4 to 8 per cent carbohydrate-based sports drink per hour, in small, frequent doses during activity. Some researchers have questioned whether adding protein to carbohydrate-containing sports beverages would offer a performance advantage to endurance athletes. Evidence so far suggests that when carbohydrate intake is optimal, protein provides no additional performance benefit.15

Glucose after activity Muscles depleted of glycogen have increased insulin sensitivity, and this enhances glucose uptake and promotes glycogen synthesis. Thus, eating high-carbohydrate foods after physical activity also enlarges glycogen stores. To accelerate the rate of glycogen storage, train normally;

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then, within two hours after physical activity, consume a high-carbohydrate meal, such as a glass of orange juice and some plain biscuits, toast, or cereal. After two hours, the rate of glycogen storage declines by almost half. This strategy is particularly important to athletes who train hard more than once a day. Chapter 4 introduces the glycaemic index and discusses the possible health benefits of eating a low-glycaemic diet. Some research suggests a low-glycaemic diet may also benefit endurance performance, but the majority of studies do not support such findings.16

Carbohydrate recommendations for athletes To postpone fatigue and maximise performance, athletes must maintain available glucose supplies for as long as they can. To do so, athletes need abundant carbohydrate each day. Recent research supports a range of carbohydrate intakes for athletes based on the athlete’s total energy needs, training needs and performance (see Table 14.4). Section 14.5 discusses how to design a high-carbohydrate diet for performance. Endurance athletes may also use a technique known as carbohydrate loading designed to maximise glycogen stores for long endurance competitions. While the original protocol for carbohydrate loading required almost a week of preparation, modern recommendations now simplify this to following a carbohydrate-rich diet (10 to 12 g of carbohydrate per kg of body weight per day) and tapering training in the 36 to 48 hours before competition.

TABLE 14.4   Recommended daily carbohydrate intakes for athletes These general research-based guidelines should be adjusted to an athlete’s energy needs, training regimen and performance. DAILY NEEDS FOR FUEL AND RECOVERY SITUATION

CARBOHYDRATE NEEDS

Sedentary or low-intensity/skills-based training

3–5 g/kg/day

Moderate exercise program (~1 hour per day)

5–7 g/kg/day

Moderate-to-high intensity endurance training program (1–3 hours per day)

6–10 g/kg/day

Heavy endurance training (>4–5 hours per day) of moderate-to-high intensity training

8–12 g/kg/day

Adapted from D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116 (2016): 501–528.

Fat use during physical activity Sports nutrition experts recommend that endurance athletes consume 20 to 35 per cent of their energy from fat to meet nutrient and energy needs and limit saturated fat intake to less than 10 per cent of total energy intake the same recommendation as for others.17 Athletes who restrict fat below 20 per cent of total energy intake may fail to consume adequate energy and nutrients. Recommendations to include vegetable oils, nuts, olives, fatty fish and other sources of health-promoting fats in the diet apply to athletes as well as to everyone else. In contrast to dietary fat, body fat stores are extremely important during physical activity, as long as the activity is not too intense. Unlike glycogen stores, the body’s fat stores can usually provide more than 300 000 kilojoules and can fuel hours of activity without running out. The fatty acids used in physical activity are liberated from the internal fat stores and from the fat under the skin. Areas that have the most fat to spare donate the greatest amounts to the blood (although they may not be the areas that appear fattest). Thus ‘spot reducing’ does not work because muscles do not ‘own’ the fat that surrounds them. Fat cells release fatty acids into the blood, not into the underlying muscles. Then the blood gives to each muscle the

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amount of fat that it needs. Proof of this is found in a tennis player’s arms – the skinfold measures of fat are the same in both arms, even though the muscles of one arm work much harder and may be larger than those of the other. A balanced fitness program that includes strength training, however, will tighten muscles underneath the fat, improving the overall appearance. Athletes who want to become ‘all muscle’ should keep in mind that some body fat is essential to good health. (Chapter 8 discusses the health risks of too little body fat.)

Duration of activity affects fat use iStock.com/CoffeeAndMilk

Early in an activity, as the muscles draw on fatty acids, blood levels fall. If the activity continues for more than a few minutes, the hormone epinephrine signals the fat cells to begin breaking down their stored triglycerides and liberating fatty acids into the blood. As physical activity continues, the blood fatty acid concentration surpasses the normal resting concentration. Thereafter, sustained moderate activity uses body fat stores as its major fuel.

Alamy Stock Photo/SuperStock

Abundant energy from the breakdown of fat can come only from aerobic metabolism.

Intensity of activity affects fat use The intensity of physical activity also affects fat use. As the intensity of activity increases, fat makes less and less of a contribution to the fuel mixture. Remember that fat can be broken down for energy only by aerobic metabolism. For fat to fuel activity, then, oxygen must be abundantly available. If a person is breathing easily during activity, the muscles are getting all the oxygen they need and are able to use more fat in the fuel mixture.

Training affects fat use Training – repeated aerobic activity – produces the adaptations that permit the body to draw more heavily on fat for fuel. Training stimulates the muscle cells to manufacture more and larger mitochondria, the ‘powerhouse’ structures of the cells that produce ATP for energy. Another adaptation is Low- to moderate-intensity aerobic exercises that can be sustained for a long time (more than that the heart and lungs become stronger and better able to deliver oxygen 20 minutes) use some glucose, but more fat, to muscles at high-activity intensities. Additionally, hormones in the body of for fuel. a trained person slow glucose release from the liver and speed up the use of fat instead. These adaptations reward not only trained athletes but all active people; a person who trains by way of aerobic activities, such as distance running or cycling, becomes well suited to the activity.

Protein use during physical activity – and between times Table 14.3 summarises the fuel uses discussed so far, but does not include the third energyyielding nutrient, protein, because it is not a major fuel used for physical activity. Nevertheless, physically active people use protein just as other people do – to build muscle and other lean tissues and, to some extent, to fuel activity. The body does, however, handle protein differently during activity than during rest.

Protein used in muscle building Synthesis of body proteins is suppressed during activity. In the hours of recovery following activity, though, protein synthesis accelerates beyond normal resting levels. As noted earlier, eating high-carbohydrate foods immediately after exercise accelerates muscle glycogen storage. For protein synthesis, the timing of dietary intake is not as critical. Eating high-quality

protein, frequently and in sufficient quantities, enhances muscle protein synthesis.18 Repeated activity, with just a slight overload, triggers the protein-dismantling and protein-synthesising equipment of each muscle cell to adapt and build the molecules and tissues it needs for the next period of activity. The physical work of each muscle cell acts as a signal to its DNA and RNA to begin producing the kinds of proteins that will best support that work. Consider running, for example. In the first difficult sessions, the body is not yet equipped to perform aerobic work easily, but with each session, the cells’ genetic material gets the message that an overhaul is needed. In the hours that follow the session, the genes send molecular messages to the proteinbuilding equipment that tell it what old structures to break down and what new structures to build. Within the limits of its genetic potential, the body responds. Running (or any aerobic activity) stimulates synthesis of mitochondria to facilitate efficient aerobic metabolism. Over time, the body adapts and running becomes easier. The body of a weightlifter responds to training, as well, but the response differs from that of aerobic training. Weightlifting stimulates synthesis of muscle fibre protein to enhance muscle mass and strength – with little change in mitochondrial protein. An athlete may add between 7 and 28 grams of protein to muscle mass each day during active muscle-building phases of training.

Protein used as fuel Not only do athletes retain more protein in their muscles, they also use more protein as fuel. Muscles speed up their use of amino acids for energy during Protein not only builds muscle but also helps fuel exercise. physical activity, just as they speed up their use of fat and carbohydrate. Still, protein contributes only about 10 per cent of the total fuel used, both during activity and during rest. The most active people of all – endurance athletes – use large amounts of all energy fuels, including protein, during performance, but they also eat more food and therefore usually consume enough protein.

Diet affects protein use during activity Diet influences how much protein is used during physical activity. People who consume diets adequate in energy and rich in carbohydrate use less protein than those who eat protein- and fat-rich diets. Recall that carbohydrates spare proteins from being broken down to make glucose when needed. Because physical activity requires glucose, a diet lacking in carbohydrate necessitates the conversion of amino acids to glucose. The same is true for a diet high in fat because fatty acids can never provide glucose. In short, to conserve protein, eat a diet adequate in energy and rich in carbohydrate.

Intensity and duration of activity affect protein use during activity The intensity and duration of activity also modifies protein use. Endurance athletes who train for more than an hour a day, engaging in aerobic activity of moderate intensity and long duration, may deplete their glycogen stores by the end of their workouts and become somewhat more dependent on body protein for energy. In contrast, anaerobic strength training does not use more protein for energy, but it does demand more protein to build muscle. Thus, the protein needs of both endurance and strength athletes are higher than those of sedentary people, but certainly not as high as the protein intakes many athletes consume.

Protein recommendations for active people As mentioned, all active people, and especially athletes in training, probably need more protein than sedentary people do. Endurance athletes, such as long-distance runners and cyclists, use more protein for fuel than strength or power athletes do, and they retain some, especially in

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the muscles used for their sport. Strength athletes, such as body builders, and power athletes, such as football players, use less protein for fuel, but they still use some and retain much more. Therefore, all athletes in training should attend to protein needs, but they should first meet their energy needs with adequate carbohydrate intakes. Without adequate carbohydrate intake, athletes will burn off as fuel the very protein that they wish to retain in muscle. How much protein, then, should an active person consume? Although the Nutrient Reference Values for Australia and New Zealand do not recommend greater than normal protein intakes for athletes, other authorities do.19 Research supports a range of protein intakes for athletes based on training experience, frequency and intensity of training sessions, and importantly, energy and carbohydrate availability (see Table 14.5). Daily protein intake goals are best met by a meal plan that includes moderate amounts (20–30 g) of high-quality protein in four to five small meals throughout the day, including within two hours following strenuous training sessions. Table 14.6 presents foods and beverages that provide 20 grams of high-quality protein. Even the highest protein recommendations can be met without protein supplements, or even without excessive servings of meat. Chapter 6 reviews the potential problems of using protein and amino acid supplements.

PUTTING COMMON SENSE TO THE TEST

Protein needs for endurance athletes are the same as those of sedentary people. FALSE

TABLE 14.5   Recommended protein intakes for athletes RECOMMENDATIONS (g/kg/day) RDI for adults Recommended intake for athletes

0.84 males 0.75 females 1.2−2.0

PROTEIN INTAKES (g/day) MALES

FEMALES

59

41

84−140

66−120

Note: Daily protein intakes are based on a 70-kg man and 55-kg woman. Adapted from D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116 (2016): 501–528.

TABLE 14.6   Selected foods and beverages providing 20 grams of high-quality protein and varying amounts of energy as shown FOOD OR BEVERAGE

SERVING SIZE

ENERGY (kJ)

Almonds

85 g

2100

Beef, lean

85 g

609

Cheese, cheddar

85 g

1450

Chicken, skinless breast

85 g

550

Eggs (white)

6 large

420

Eggs (whole)

3 large

1130

Milk, reduced fat

600 mL

1070

Tofu

225 g

780

Tuna, light, canned in water

85 g

290

Yoghurt, Greek-style

225 g

550

REVIEW IT

The mixture of fuels that the muscles use during physical activity depends on diet, the intensity and duration of the activity, and training. During intense activity, the fuel mix is mostly glucose, whereas during less intense, moderate activity, fat makes a greater contribution. With endurance training, muscle cells adapt to store more glycogen and to rely less on glucose and more on fat for energy. Athletes in training may need more protein than sedentary people do, but they typically eat more food as well and therefore obtain enough protein without using supplements.

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14.3  Vitamins and minerals to support activity

Many of the vitamins and minerals assist in releasing energy from fuels and in transporting oxygen. This knowledge has led many people to believe, mistakenly, that vitamin and mineral supplements offer physically active people both health benefits and athletic advantages. (Review Highlight 10 for a discussion of vitamin and mineral supplements, and see Highlight 14, which explores supplements and other products people use in the hope of enhancing athletic performance.)

Nutrient supplements do not enhance the performance of well-nourished people and most athletes do not need them. Deficiencies of vitamins and minerals, however, do impede performance. Regular, strenuous, physical activity increases energy needs, and if athletes and active people select nutrient-dense foods to meet their increased energy needs, they will most likely meet their vitamin and mineral needs as well. As Highlight 8 mentions, some athletes who struggle to meet low body weight requirements may eat so little food that they fail to obtain all the nutrients they need. The practice of ‘making weight’ is opposed by many health and fitness organisations, but for athletes who choose this course of action, a single daily multivitamin–mineral supplement that provides no more than the NRVs for nutrients may be beneficial. In addition, some athletes simply do not eat enough food to maintain a healthy body weight during times of intense training or competition. For these athletes as well, a daily multivitamin-mineral supplement may be helpful. Some athletes believe that taking vitamin or mineral supplements directly before competition will enhance performance. These beliefs are contrary to scientific reality. Most vitamins and minerals function as small parts of larger working units. After absorption into the blood, these nutrients travel to the cells for assembly with the appropriate other parts so that they can do their work. This takes time – hours or days. Vitamins or minerals taken For perfect functioning, every nutrient is needed. right before an event are useless for improving performance, even if the person is actually experiencing deficiencies of them.

Iron: a mineral of concern Physically active young women, especially those who engage in endurance activities, such as distance running, are prone to iron deficiency.20 Habitually low intakes of iron-rich foods, high iron losses through menstruation, and the high demands of muscles for the iron-containing electron carriers of the mitochondria and the muscle protein myoglobin can cause iron deficiency in physically active young women. In addition, endurance activities temporarily increase the release of hepcidin, which limits iron absorption (see Chapter 13).21 Adolescent female athletes who avoid or limit red meat may be particularly vulnerable to iron deficiency. As Chapter 13 explained, the bioavailability of iron is often poor in vegetarian diets. To protect against iron deficiency, athletes who limit meat need to select good dietary sources of iron (e.g. fortified cereals, legumes, nuts and seeds) and include vitamin C-rich foods with each meal. As long as vegetarian athletes, like all athletes, consume enough nutrient-dense foods, they can perform as well as anyone.

PUTTING COMMON SENSE TO THE TEST

Male bodybuilders are the most ‘at risk’ group for iron deficiency. FALSE

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Dietary supplements

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Iron-deficiency anaemia

Iron is an essential component of haemoglobin, the protein that transports oxygen throughout the body.

Iron-deficiency anaemia impairs physical performance because the haemoglobin in red blood cells is needed to deliver oxygen to the cells for energy metabolism. Without adequate oxygen, an active person cannot perform aerobic activities and tires easily. Iron deficiency without clinical signs of anaemia may also impair physical performance.

Sports anaemia Early in training, athletes may develop low blood haemoglobin for a while. This condition, sometimes called sports anaemia, is not a true iron-deficiency condition. Strenuous aerobic activity promotes destruction of the more fragile, older red blood cells, and the resulting clean-up work reduces the blood’s iron content temporarily. Strenuous activity also expands the blood’s plasma volume, thereby reducing the red blood cell count per unit of blood. The resulting low haematocrit looks like iron-deficiency anaemia, but it is not the same. In sports anaemia, the red blood cells do not diminish in size or number as in anaemia, so the oxygen-carrying capacity is not hindered. Most researchers view sports anaemia as an adaptive, temporary response to endurance training. Iron-deficiency anaemia requires iron supplementation, but sports anaemia does not.

Iron recommendations for athletes The best strategy for maintaining adequate iron nutrition varies, depending on individual cases. Women who menstruate may border on iron deficiency even without the iron losses incurred by physical activity. Active teens of both genders have high iron needs because they are growing. Especially for women and teens, then, prescribed supplements may be needed to correct iron deficiencies. Physicians use the results of blood tests to determine whether such supplementation is needed. (Review Chapter 13 for many more details about iron, and see Appendix E for a description of the tests used in assessing its status.)

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REVIEW IT

With the possible exception of iron, well-nourished active people and athletes do not need nutrient supplements. Female athletes need to pay special attention to their iron needs.

14.4  Fluids and electrolytes to support activity

The need for water far surpasses the need for any other nutrient. The body relies on watery fluids as the medium for all its life-supporting activities, and if it loses too much water, its wellbeing will be compromised. Obviously, the body loses water via sweat. Breathing uses water, too, exhaled as vapour. During physical activity, water losses from both routes are significant, and dehydration becomes a threat. Dehydration’s first symptom is fatigue – a water loss of greater than 2 per cent of body weight can reduce a person’s capacity to do muscular work.22 With a water loss of about 7 per cent, a person is likely to collapse.

Temperature regulation

To prevent dehydration and the fatigue that accompanies it, drink liquids before, during and after physical activity.

As Chapter 7 discusses, working muscles produce heat as a by-product of energy metabolism. During intense activity, muscle heat production can be 15 to 20 times greater than at rest. The body cools itself by sweating. Each litre of sweat dissipates almost 2400 kilojoules of heat, preventing a rise

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in body temperature of almost 10 ºC. The body routes its blood supply through the capillaries just under the skin, and the skin secretes sweat to evaporate and cool the skin and the underlying blood. The blood then flows back to cool the deeper body chambers.

Hyperthermia In hot, humid weather, sweat doesn’t evaporate well because the surrounding air is already laden with water. In hyperthermia, body heat builds up and triggers maximum sweating, but without sweat evaporation, little cooling takes place. In such conditions, active people must take precautions to prevent heat stroke. To reduce the risk of heat stroke, drink enough fluid before and during the activity, rest in the shade when tired and wear lightweight clothing that allows sweat to evaporate. (The danger of rubber or heavy suits that supposedly promote weight loss during physical activity is that they promote profuse sweating, prevent sweat evaporation and invite heat stroke.) If you ever experience any of the symptoms of heat stroke listed in Table 14.7, stop your activity, sip cool fluids, seek shade and ask for help. Heat stroke can be fatal, people sometimes die of it, and these symptoms demand attention.

TABLE 14.7   Symptoms of heat stroke and hypothermia compared HEAT STROKE

HYPOTHERMIA

• Clumsiness, stumbling • Confusion, dizziness, other mental changes, loss of consciousness • Flushed skin (skin may turn red as body temperature rises) • Muscle cramping (early symptom) • Nausea and vomiting • Rapid breathing • Rapid heart rate • Sudden cessation of sweating (hot, dry, skin) • Throbbing headache

• Clumsiness, loss of coordination • Confusion, disorientation, other mental changes, loss of consciousness • Drowsiness • Shivering (early symptom) • Cessation of shivering (late symptom) • Slurred speech • Slow breathing • Slow heart rate

Adapted from United States Centers for Disease Control and Prevention, http://www.cdc.gov.

Hypothermia

In cold weather, hypothermia, or low body temperature, can be as serious as heat stroke is in hot weather. Inexperienced, slow runners participating in long races on cold or wet, chilly days are especially vulnerable to hypothermia. Slow runners who produce little heat can become too cold if clothing is inadequate. Early symptoms of hypothermia include feeling cold, shivering, apathy and social withdrawal. As body temperature continues to fall, shivering may stop and disorientation, slurred speech and change in behaviour or appearance set in (see Table 14.7). People with these symptoms soon become helpless to protect themselves from further body heat losses. Even in cold weather, however, the active body still sweats and still needs fluids. The fluids should be warm or at room temperature to help protect against hypothermia.

Fluid replacement via hydration Endurance athletes can easily lose 1.5 litres or more of fluid during each hour of activity. Table 14.8 presents a suggested schedule of hydration for physical activity. To prepare for fluid losses, a person must hydrate before activity; to replace fluid losses, the person must rehydrate during and after activity. Even then, in hot weather, the GI tract may not be able to absorb enough water fast enough to keep up with sweat losses, and some degree of dehydration may be inevitable. Athletes who know their body’s hourly sweat rate can strive to replace the total amount of fluid lost during activity to prevent dehydration.

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TABLE 14.8   A suggested hydration schedule for physical activity WHEN TO DRINK

AMOUNT OF FLUID

≥4 hours before activity

65 mL per 10 kg

2 hours before activity, if heavy sweating is expected

Add 40 mL per 10 kg

Every 15 minutes during activity

Drink enough to minimise loss of body weight, but don’t drink too much

After activity

≥100 mL for each 100 g of body weight losta

Drinking 2 cups of fluid every 20 to 30 minutes after exercise until the total amount required is consumed is more effective for rehydration than drinking the needed amount all at once. Rapid fluid replacement after exercise stimulates urine production and results in less body water retention.

a 

Shutterstock.com/Chuck Wagner

Adapted from D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116 (2016): 501–528.

Athletes who are preparing for competition are often advised to drink extra fluids in the days before the event, especially if they are still training. The extra water is not stored in the body, but drinking extra water ensures maximum hydration at the start of the event. Full hydration is imperative for every athlete, both in training and in competition. The athlete who arrives at an event even slightly dehydrated begins with a disadvantage. What is the best fluid for an exercising body? For non-competitive, everyday active people, plain, cool water is recommended, especially in warm weather, for two reasons: (1) water rapidly leaves the digestive tract to enter the tissues where it is needed, and (2) water cools the body from the inside out. For endurance athletes, carbohydrate-containing Water is the best fluid for most physically active beverages may be appropriate. Fluid ingestion during the event has the people, but some consumers prefer the flavours of sports drinks. dual purposes of replenishing water lost through sweating and providing a source of carbohydrate to supplement the body’s limited glycogen stores. Many carbohydrate-containing sports drinks are marketed for active people; a later section compares them with water.

Electrolyte losses and replacement When a person sweats, small amounts of electrolytes – the electrically charged minerals sodium, potassium, chloride and magnesium – are lost from the body along with water. Losses are greatest in beginners; training improves electrolyte retention. To replenish lost electrolytes, a person ordinarily needs only to eat a regular diet that meets energy and nutrient needs. In events lasting more than one hour, sports drinks may be needed to replace fluids and electrolytes. Endurance athletes considering the use of salt tablets to replace sodium are advised to consult their healthcare provider first. Salt tablets can worsen dehydration and impair performance, increase potassium losses, irritate the stomach and cause vomiting.

APPLICATIONS OF NUTRITIONAL RESEARCH Hyponatraemia When athletes compete in endurance sports lasting longer than three hours, replenishing electrolytes is crucial. If athletes sweat profusely over a long period of time and do not replace lost sodium, a dangerous condition known as hyponatraemia may result. Research shows that some athletes who sweat profusely may also lose more sodium in their sweat than others – and are prone to debilitating heat cramps. These athletes lose twice as much

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sodium in sweat as athletes who don’t cramp. Depending on individual variation, exercise intensity and changes in ambient temperature and humidity, sweat rates for these athletes can exceed 2 litres per hour. Hyponatraemia may also occur when endurance athletes drink such large amounts of water over the course of a long event that they overhydrate, diluting the body’s fluids to such an extent that the sodium concentration becomes extremely low. Current guidelines advise athletes to use their thirst as a guide to avoid overhydration and hyponatraemia.23 During long competitions, when athletes lose sodium through heavy sweating and consume excessive amounts of liquids, especially water, hyponatraemia becomes likely. Some athletes may still be vulnerable to hyponatraemia even when they drink sports drinks during an event. Sports drinks do contain sodium, but sometimes too little to replace sweat losses. Still, sports drinks do offer more sodium than plain water. To prevent hyponatraemia, athletes need to replace sodium during prolonged events. Sports drinks, salty pretzels, and other sodium sources can provide sodium during long competitions. Some athletes may need beverages with higher sodium concentrations than commercial sports drinks. In the days before the event, especially an event in the heat, athletes should not restrict salt in their diets. The symptoms of hyponatraemia are similar to, but not the same as, those of dehydration.

Sports drinks Hydration is critical to optimal performance. As stated earlier, water best meets the fluid needs of most people, yet manufacturers market many good-tasting sports drinks for active people. The term ‘sports drink’ generally refers to beverages that contain carbohydrates and electrolytes in specific concentrations, and they are the focus of this discussion. What do sports drinks have to offer?

Fluid Sports drinks offer fluids to help offset the loss of fluids during physical activity, but plain water can do this, too. Alternatively, diluted fruit juices or flavoured water can be used if preferred to plain water.

Glucose

Sports drinks offer simple sugars or glucose polymers that help maintain hydration and blood glucose and enhance performance as effectively as, or maybe even better than, water. Such measures are especially beneficial for strenuous endurance activities lasting longer than one hour, during intense activities or during prolonged competitive games that demand repeated intermittent activity.24 Sports drinks are also suitable for events lasting less than one hour, although plain water is appropriate as well. Fluid transport to the tissues from beverages containing up to 8 per cent glucose is rapid. Most sports drinks contain about 7 per cent carbohydrate (about half the sugar of ordinary soft drinks, or about 5 teaspoons in each 350 mL). Less than 6 per cent carbohydrate may not enhance performance, and more than 8 per cent may cause abdominal cramps, nausea and diarrhoea. Although glucose can enhance endurance performance in strenuous competitive events, for the moderate exerciser who is attempting to lose weight it can be counterproductive if weight loss is the goal. Glucose is sugar and provides only empty kilojoules – no vitamins or minerals. Most sports drinks provide between 200 and 400 kJ per cup (250 mL).

Sodium and other electrolytes Sports drinks offer sodium and other electrolytes to help replace those lost during physical activity. Sodium in sports drinks also helps to increase the rate of fluid absorption from the GI

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Symptoms of hyponatraemia include: • severe headache • vomiting • bloating, puffiness from water retention (shoes tight, rings tight) • confusion • seizure.

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tract and maintain plasma volume during activity and recovery. Most physically active people do not need to replace the minerals lost in sweat immediately; a meal eaten within hours of competition replaces these minerals soon enough. Most sports drinks are relatively low in sodium, however, so those who choose to use these beverages run little risk of excessive intake.

Good taste Manufacturers reason that if a drink tastes good, people will drink more, thereby ensuring adequate hydration. For athletes who prefer the flavours of sports drinks over water, it may be worth paying for good taste to replace lost fluids. For athletes who exercise for one hour or more, sports drinks provide an advantage over water. Sports drinks may also be beneficial for athletes who: • exercise on an empty stomach • consume too little carbohydrate • want to load carbohydrates • want to gain weight • train at altitude or in extreme weather • had diarrhoea (or vomiting) recently • drink inadequate amounts of water. For most physically active people, though, water is the best fluid to replenish lost fluids. The most important thing to do is drink when you feel thirsty.

Enhanced water

Beer facts: • Beer is not carbohydrate-rich – it is kilojoule-rich, but only one-third of its energy is from carbohydrates. The rest are from alcohol. • Beer is mineral-poor – it contains a few minerals, but to replace the minerals lost in sweat, athletes need good sources, such as fruit juices. • Beer is vitamin-poor – it contains traces of some B vitamins, but it cannot compete with food sources. • Beer is a fluid – it is also a diuretic and causes the body to lose valuable fluid.

Another beverage often marketed to athletes and active people is enhanced water. Enhanced waters are lightly flavoured waters with added sugars, vitamins, minerals, and in some cases, protein. Many enhanced waters are neither natural nor healthy. In fact, most enhanced waters contain small amounts of only a few minerals, some of the B vitamins and sometimes vitamin C or vitamin E. In the context of daily needs, the vitamins and minerals in these drinks do not add up to much. For example, it takes a litre of most of these beverages to provide only 10 per cent of the RDI for iron or calcium. Quite simply, enhanced waters are not a substitute for eating nutrient-rich fruits and vegetables. Enhanced waters may not be harmful, but they can be expensive, and most people do not need them. If the flavour of enhanced waters encourages greater fluid intake, then they may offer some advantage, but serious endurance athletes need the carbohydrate–electrolyte sports drinks discussed earlier.

Poor beverage choices: caffeine and alcohol Athletes, like others, sometimes drink beverages that contain caffeine or alcohol, both of which can influence physical performance.

Caffeine Caffeine is a stimulant, and athletes sometimes use it to enhance performance, as Highlight 14 explains. Carbonated soft drinks, with or without caffeine, may not be a wise choice for athletes – bubbles make a person feel full quickly and so limit fluid intake. Some of the increasingly popular energy drinks contain amounts of caffeine equivalent to that in a cup or more of coffee. When used in excess or in combination with stimulants or other unregulated substances, energy drinks can hinder performance and are potentially dangerous.25 Another reason energy drinks should not be used for fluid replacement during athletic events is that the carbohydrate concentrations are too high for optimal fluid absorption.

Alcohol Some athletes mistakenly believe that they can replace fluids and load up on carbohydrates by drinking beer. A 350-mL beer provides 13 grams of carbohydrate – one-third the amount

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of carbohydrate in a glass of orange juice the same size. In addition to carbohydrate, beer also contains alcohol, of course. Energy from alcohol breakdown generates heat, but it does not fuel muscle work because alcohol is metabolised in the liver. It is difficult to overstate alcohol’s detrimental effects on physical activity. Alcohol alters perceptions; slows reaction time; reduces strength, power and endurance; and hinders accuracy, balance, eye-hand coordination and coordination in general – all opposing optimal athletic performance. In addition, it interferes with judgement, thereby compromising safety in sports. Many sports-related fatalities and injuries involve alcohol or other drugs. Clearly, alcohol impairs performance. Anyone who does drink should at least not drink alcohol before exercising. After exercising the preferred drink is water – in abundance. REVIEW IT

Active people need to drink plenty of water; endurance athletes need to drink both water and carbohydrate-containing beverages, especially during training and competition. During events lasting longer than three hours, athletes need to pay special attention to the replacement of sodium losses to prevent hyponatraemia.

14.5  Diets for physically active people No one diet best supports physical performance. Active people who choose foods within the framework of the diet-planning principles presented in Chapter 2 can design many excellent diets.

Above all, keep in mind that water is depleted more rapidly than any other nutrient. A diet to support fitness must provide water, energy and all the other nutrients.

Water Even casual exercisers must attend conscientiously to their fluid needs. A thirsty athlete should not wait to hydrate. As mentioned A variety of foods is the best source of nutrients for athletes. earlier, however, overhydration may lead to hyponatraemia. Adequate hydration is crucial for every athlete, both in training and in competition. To find out how much water is needed to replenish activity losses, weigh yourself before and after the activity – the difference is almost all water.

Nutrient density A healthful diet is based on nutrient-dense foods – foods that supply adequate vitamins and minerals for the energy they provide. Active people need to eat both for nutrient adequacy and for energy – and energy needs can be extremely high. For example, during training, meals for some Olympic athletes provide as much as 40 000 kilojoules a day. Still, a nutrient-rich diet remains vital for adequacy’s sake. Nutrients are also vital to support performance.

Carbohydrate Full glycogen stores are critical to athletes and other highly active people. Guidelines to provide high carbohydrate availability for athletes are based on the athlete’s weight and the characteristics of training sessions and competitions (review Table 14.4 in Section 14.2). As discussed earlier, the timing of carbohydrate intake is also important for maximising carbohydrate availability. On two occasions, the active person’s regular high-carbohydrate, fibre-rich diet may require temporary adjustment. Both of these exceptions involve training for competition rather than for fitness in general. One special occasion is the pre-game meal, when fibre-rich, bulky foods are best avoided. The pre-game meal is discussed in a later section.

Carbohydrate recommendation for endurance athletes in heavy training: 8–12 g/kg body weight

Polara Studios, Inc.

Choosing a diet to support fitness

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The other occasion is a period during intensive training, when energy needs may be so high as to outstrip the person’s capacity to eat enough food to meet them. In this case, the athlete may want to rely on concentrated carbohydrate foods, such as dried fruits, sweet potatoes, and nectars, and even high-fat foods, such as avocados and nuts. Some athletes use commercial high-carbohydrate liquid supplements to obtain the carbohydrate and energy needed for intense training and top performance. These supplements do not replace regular food; they are meant to be used in addition to it. Unlike the sports drinks discussed earlier, these highcarbohydrate supplement beverages are too concentrated to be used to replace fluids.

Protein In addition to carbohydrate and some fat (and the energy they provide), physically active people need protein. Meats and milk products are rich protein sources but recommending that active people emphasise these foods is narrow advice. As mentioned repeatedly, active people need diets rich in carbohydrate, and of course, meats have none to offer. Legumes, whole grains and vegetables provide some protein with abundant carbohydrate. Table 14.5, in Section 14.2, shows recommended protein intakes for active people.

CURRENT RESEARCH IN NUTRITION A Mediterranean diet promotes exercise endurance A Mediterranean diet is one abundant in fruits, vegetables, wholegrains, legumes and olive oil. It also features fish and poultry more so than red meat. Heart health is one of the key health areas linked to a Mediterranean diet, but researchers are also looking at a range of other health conditions. One of the lesser studied areas is how a Mediterranean diet may help to improve sports performance. When it comes to sport, good nutrition is a cornerstone of performing at a person’s best. A Mediterranean diet is one rich in nutrients linked to positive exercise benefits, so could a switch to this way of eating promote real-world sports performance benefits? In a small proof-of-concept study, a research team from Saint Louis University recruited eleven healthy and recreationally active men and women in their late twenties.26 Each person undertook exercise performance tests both before and after being randomly allocated to follow a typical Western diet or a Mediterranean diet for four days. After one to two weeks break, each person swapped to the alternative diet for four days. The key result from the trial was a 6 per cent improvement in 5-kilometre run time when following the Mediterranean diet. The faster time was achieved despite having similar heart rates and ratings of perceived exertion compared to when on the Western diet. Performance on the other exercise tests, which included anaerobic exercise tests, peak power output, vertical jump and hand grip strength, showed no clear difference between the different diets. On face value, this points to nutrients in the Mediterranean diet influencing metabolic pathways involved in aerobic exercise rather than shorter more-intense anaerobic exercise. With only 11 people in the study, and the short duration of the diet, it is still early days to say if there is a clear sports performance benefit. For athletes with less than a stellar diet, there could be merit in taking heed of this latest research and making the smart choice to eating healthier with a Mediterranean twist.

Meals before and after competition No single food improves speed, strength or skill in competitive events, although some kinds of foods do support performance better than others, as already explained. Still, a competitor may eat a particular food before or after an event for psychological reasons. One eats a steak the night before wrestling. Another eats a spoonful of honey five minutes after diving. These practices are harmless and should be respected.

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Pre-game meals Science indicates that the pre-game meal or snack should include plenty of fluids and be light and easy to digest. It should provide between 1200 and 3300 kilojoules, primarily from carbohydrate-rich foods that are familiar and well tolerated by the athlete. The meal should end three to four hours before competition to allow time for the stomach to empty before exertion. The larger the meal, the more time needed for digestion. Thus, a full meal providing plenty of carbohydrate may be eaten three or more hours before an event, a small meal (1500 to 2000 kJ) may be eaten two to three hours before an event, and a small, highcarbohydrate snack may be appropriate one hour before an event. Breads, potatoes, pasta and fruit juices – that is, carbohydrate-rich foods low in fat and fibre – are the staples of the best pre-game meal (see Figure 14.3 for some examples). Bulky, fibre-rich foods, such as raw vegetables or wholegrain cereals, although usually desirable, are best avoided just before competition. Fibre in the digestive tract attracts water and can cause stomach discomfort during performance. Liquid meals are easy to digest, and many such meals are commercially available. Alternatively, athletes can mix fat-free milk or juice, frozen fruits and flavourings in a blender.

High-carbohydrate, liquid pre-game fruit smoothie ideas include: • apple juice, frozen banana and 1 tablespoon of plain yoghurt • pineapple juice, frozen strawberries and several mint leaves • reduced-fat milk, frozen banana and vanilla essence.

FIGURE 14.3   Examples of high-carbohydrate pre-game meals

Matthew Farruggio

Matthew Farruggio

Matthew Farruggio

Pre-game meals should be eaten three to four hours before the event and provide 1200 to 3300 kilojoules, primarily from carbohydrate-rich foods. Each of these sample meals provides at least 65 per cent of total kilojoules from carbohydrate.

Recovery meals Athletes who perform intense practice sessions several times a day or compete for hours on consecutive days need to quickly replenish their glycogen stores between sessions. As mentioned earlier, eating high-carbohydrate foods after physical activity enhances glycogen storage, just as eating high-quality protein foods helps stimulate protein synthesis. Because people are usually not hungry immediately following physical activity, a carbohydratecontaining beverage such as low-fat milk may be preferred. A 500-millilitre serving of chocolate milk, taken within an hour or two following exercise, can both maintain muscle glycogen stores and increase muscle protein synthesis. If an active person does feel hungry after an event, then foods high in carbohydrate, moderate in protein, and low in fat and fibre are the ones to choose – similar to those recommended prior to competition. REVIEW IT

The person who wants to excel physically will apply accurate nutrition knowledge along with dedication to rigorous training. A diet that provides ample fluid and includes a variety of nutrient-dense foods in quantities to meet energy needs will enhance not only athletic performance, but overall health as well. Carbohydrate-rich foods that are light and easy to digest are recommended for both the pre-game and the postgame meal.

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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Regular exercise can reduce the risk of developing some types of cancers. TRUE

4 Protein needs for endurance athletes are the same as those of sedentary people. FALSE





Lifelong physical activity may help to protect against colon cancer, breast cancer and some other cancers.

2 Creatine phosphate is a reliable energy reserve for distance runners. FALSE

Creatine phosphate can only supply energy for around 10 seconds, and so is used in sprinting.

5 Male bodybuilders are the most ‘at risk’ group for iron deficiency. FALSE

3 As exercise intensity increases, glycogen utilisation also increases. TRUE

The combination of the impact stress on the body and depletion of glycogen stores means endurance athletes have much higher protein requirements than a sedentary person.

Physically active young women, especially those who engage in endurance activities, such as distance running, are most prone to iron deficiency.

Anaerobic glycolysis becomes more important to meet ATP needs as exercise intensity increases to maximum.

NUTRITION PORTFOLIO The foods and beverages you eat and drink provide fuel and other nutrients to support your physical activity. • Describe your daily physical activities and how they compare with recommendations to be physically active for at least 30 minutes, and preferably 60 minutes, a day on most or all days of the week.

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Estimate your daily fluid intake, making note of whether you drink fluids, especially water, before, during and after physical activity. Evaluate the carbohydrate contents of your diet and consider whether it would meet the needs of a physically active person.

STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1 Physical inactivity is linked to all of the following diseases except: a cancer b diabetes c emphysema d hypertension. 2 The progressive overload principle can be applied by performing: a an activity less often b an activity with more intensity c an activity in a different setting d a different activity each day of the week. 3 The process that regenerates glucose from lactate is known as the: a Cori cycle b ATP–CP cycle c TCA cycle d cardiac output cycle. 4 ‘Hitting the wall’ is a term runners sometimes use to describe: a dehydration b competition c indigestion d glucose depletion.

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What is the technique that endurance athletes use to maximise glycogen stores? a Aerobic training. b Muscle conditioning. c Carbohydrate loading. d Progressive overloading. Conditioned muscles rely less on _____ and more on _____ for energy. a protein; fat b fat; protein c glycogen; fat d fat; glycogen. What is an approximate target for protein intake for endurance athletes? a 0.8 g/kg/day b 0.8–1.2 g/kg/day c 1.2–2.0 g/kg/day d 3.0 g/kg/day. Physically active young women, especially those who are endurance athletes, are prone to: a energy excess b iron deficiency c protein overload d vitamin A toxicity.

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The body’s need for _____ far surpasses its need for any other nutrient. a water b protein c vitamins d carbohydrate.

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10 A recommended pre-game meal includes plenty of fluids and provides between: a 1200 and 3000 kJ, mostly from fat-rich foods b 200 and 400 kJ, mostly from high-fibre foods c 4000 and 8000 kJ, mostly from protein-rich foods d 1200 and 3000 kJ, mostly from carbohydrate-rich foods.

REVIEW QUESTIONS 1 2 3 4 5 6 7

Describe why physical activity complements a wellbalanced diet to improve health. (Section 14.1) Explain the differences between strength and endurance exercise. (Section 14.1) Define cardiorespiratory conditioning and list some of its benefits. (Section 14.1) What types of activity are anaerobic? Which are aerobic? (Section 14.2) Describe the relationships among energy expenditure, type of activity and oxygen use. (Section 14.2) What factors influence the body’s use of glucose during physical activity? How? (Section 14.2) What factors influence the body’s use of fat during physical activity? How? (Section 14.2)

8

What factors influence the body’s use of protein during physical activity? How? (Section 14.2) 9 How do protein recommendations differ between athletes and the general population? (Section 14.2) 10 Why are some athletes likely to develop irondeficiency anaemia? Compare iron-deficiency anaemia and sports anaemia, explaining the differences. (Section 14.3) 11 Discuss the impact dehydration has on performance and strategies that can be used to prevent dehydration. (Section 14.4) 12 Describe the importance of carbohydrates as part of a healthy diet for athletic performance. (Section 14.5)

NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Examine how physical activity can become a vital component of children’s education at the Australian Council for Health, Physical Education and Recreation website: http://www.achper.org.au • Learn about the activities of sports dietitians at the Sports Dietitians Australia website: http://www. sportsdietitians.com.au

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Find fitness information at the Cooper Institute site: http://www.cooperinst.org Find information on sports drinks and other nutrition and fitness topics at the Australian Institute of Sport Nutrition site: https://www.ais.gov.au/nutrition Find information on sports drinks and other nutrition and fitness topics at the Gatorade Sports Science Institute site: https://www.gssiweb.org/en

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HIGHLIGHT

14

14.6 SUPPLEMENTS AS ERGOGENIC AIDS

Athletes gravitate to promises that they can enhance their performance by taking pills, powders or potions. Unfortunately, they often hear such promises from their coaches and peers, who advise them to use dietary supplements, take drugs or follow procedures that claim to deliver results with little effort. When such performanceenhancing aids are harmless, they are only a waste of money; when they impair performance or harm health, they waste athletic potential and cost lives. This highlight looks at scientific evidence for and against dietary supplements and hormonal preparations available to athletes.

Ergogenic aids Many substances or treatments claim to be ergogenic, meaning work enhancing. In connection with athletic performance, ergogenic aids are substances or treatments that purportedly improve athletic performance above and beyond what is possible through training. For practical purposes, most ergogenic aids can be categorised as follows: • those that perform as claimed • those that may perform as claimed but for which there is currently insufficient evidence

• those that do not perform as claimed • those that are dangerous, banned or illegal, and therefore should not be used. For the vast majority of ergogenic aids, research findings do not support those claims.1 Athletes who hear that a product is ergogenic should ask who is making the claim and who will profit from the sale. Chapter 6 includes a discussion on protein powders and amino acid supplements. Athletes who supplement their diets with products promoted to improve athletic performance should be aware that some supplements are contaminated with illegal substances, such as steroids, that are not listed on the label.2 Using these contaminated supplements increases the risks of harming the athlete’s health and testing positive on drug tests.

Dietary supplements that perform as claimed Among the extensive array of dietary supplements and other ergogenic aids that athletes use, a few seem to live up to the claims made for them. Convenient dietary supplements, caffeine, creatine, sodium bicarbonate, betaalanine, and dietary nitrate are the examples discussed here.

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Convenient dietary supplements

Training hard is where most of the performance gains are made for athletes.

Ready-to-drink supplements, such as liquid meal replacers and energy drinks, energy bars and energy gels, are convenient dietary supplements for athletes and active people, especially when time is limited. Many such products appeal to athletes by claiming to provide ‘complete’ nutrition. These supplements usually taste good and provide extra carbohydrate and food energy, but they fall short of providing ‘complete’ nutrition. They can be useful as a pre-game meal or a between-meal snack, but they should not replace regular meals. Liquid meal replacers may help a nervous athlete who cannot tolerate solid food on the day of an event. A liquid meal two to three hours before competition can supply some of the fluid and carbohydrate needed in a pregame meal, but a smoothie of low-fat milk or juice and frozen low-fat yoghurt or frozen fruit (e.g. strawberries or bananas) can do the same thing less expensively.

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Caffeine Caffeine is a stimulant that elicits a number of physiological and psychological effects in the body. It may enhance alertness and reduce the perception of fatigue. Some research supports the use of caffeine to enhance endurance and, to some extent, to enhance short-term, high-intensity exercise performance.3 In 2004, the World Anti-Doping Agency, established by the International Olympic Committee, removed caffeine from its list of prohibited substances. To that end, many athletes consume caffeine in coffee, tea, energy drinks, energy shots, gels, gums, and other products to provide an energy boost during sports. Caffeine may stimulate fatty acid release during endurance activity, but in contrast to what was previously thought, caffeine does not slow muscle glycogen use. Light activity before a workout also stimulates fat release and, unlike caffeine, warms the muscles and connective tissues, making them flexible and resistant to injury. The possible benefits of caffeine use must be weighed against its adverse effects – stomach upset, nervousness, irritability, headaches and diarrhoea. Caffeinated energy drinks can have harmful cardiovascular side effects, such as increased blood pressure and even sudden cardiac arrest.4 The effects of their long-term use remain unknown. Caffeine-containing beverages should be used in moderation, if at all, and in addition to other fluids, not as a substitute for them.

Creatine

Interest in – and use of – creatine supplements to enhance performance during intense activity has grown dramatically in the last few years. Power athletes, such as weightlifters, use creatine supplements to enhance stores of the high-energy compound creatine phosphate (CP) in muscles. Theoretically, the more creatine phosphate in muscles, the higher the intensity at which an athlete can train. High-intensity training stimulates the muscles to adapt, which, in turn, improves performance. Research suggests that creatine supplementation does enhance performance of short-term, repetitive, highintensity activity, such as weightlifting and sprinting.5 Creatine may improve performance by increasing muscle strength and size, cell hydration or glycogen loading capacity. In contrast, creatine supplementation has not been shown to benefit endurance activity. The question of whether short-term use (up to a year) of creatine supplements (up to 5 g per day) is safe continues to be studied, but so far, the supplements are viewed to be safe for healthy adults.7 More research is needed, however, to confirm the safety of larger doses and long-term creatine use. One side effect of creatine supplementation that no one disputes is weight gain.

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For some athletes, weight gain, especially muscle gain, is beneficial, but for others, it is not. Some medical and fitness experts voice concern that, like many performance-enhancement supplements before it, creatine is being taken in huge doses (up to 30 g per day) before evidence of its value has been ascertained. Even people who eat red meat, which is a creatine-rich food, do not consume nearly the amount supplements provide. (Creatine content varies, but on average, pork, chicken and beef provide 250–650 mg per 100 g.) Despite the uncertainties, creatine supplements are not illegal in international competition. The American Academy of Pediatrics strongly discourages the use of creatine supplements, as well as the use of any performanceenhancing substance in adolescents younger than 18 years old.

Sodium bicarbonate During short-term, high-intensity activity, acid and carbon dioxide accumulate in the blood and muscles. Sodium bicarbonate (0.3 g per kg of body weight) ingested prior to high-intensity sports performance buffers the acid and neutralises the carbon dioxide, thereby maintaining muscle pH levels closer to normal and enhancing exercise capacity.7 Sodium bicarbonate supplementation may cause unpleasant side effects, such as diarrhoea, in some athletes.

Beta-alanine

Beta-alanine is a nonessential amino acid that has recently received much attention from exercise researchers.8 Beta-alanine is the rate-limiting precursor for the synthesis of the dipeptide carnosine. Carnosine occurs in high concentrations in skeletal muscle and is one of the primary buffering substances available in muscles. Supplementation with beta-alanine has been shown to raise the concentration of muscle carnosine, which enhances the muscles’ buffering capacity.9 This enhanced buffering is especially beneficial to high-intensity exercise performance, such as sprinting. The only known adverse side effect of beta-alanine supplementation is a ‘pins and needles’ sensation that occurs with high (more than 800 mg) single doses.

Dietary nitrate Nitrate is an inorganic compound present in both air and water, as well as in certain vegetables (e.g. spinach, beets, celery, radishes and lettuce). Nitrate is also a common food preservative added to processed meats, such as bacon, sausages, hot dogs and lunch meats. As a supplement, dietary nitrate (either as beetroot juice or sodium nitrate) may improve athletic performance, and has sparked a flurry of intense, ongoing research.10

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Once ingested, nitrate is converted to nitrite, which circulates in the blood. When oxygen availability is low (as can occur during exercise), nitrite can be converted to nitric oxide. Nitric oxide, an important signalling molecule, improves the muscles’ efficiency in using oxygen. By enhancing nitric oxide bioavailability, dietary nitrate supplementation reduces oxygen consumption; improves performance during moderate walking, running, rowing and cycling; and improves exercise tolerance at more vigorous intensities. Despite such findings, some studies of elite or highly trained athletes fail to show performance benefits following nitrate supplementation; such athletes may already be performing at their maximum oxygen efficiency, or perhaps they require larger doses of nitrate to elicit benefits.11 Additional research is needed to determine how age, health and fitness status, type of activity, and other factors influence the effects of nitrate supplementation on athletic performance. The safety of long-term nitrate supplementation also needs to be addressed.

Dietary supplements that may perform as claimed For some dietary supplements, it is just too early to tell whether they deliver on the promises made for them because research thus far is inconclusive. One example of a supplement that may perform as claimed, but for which there is insufficient evidence of efficacy is beta-hydroxymethylbutyrate (HMB), a metabolite of the amino acid leucine. Some research suggests that supplementing the diet with HMB during training increases muscle mass, power, and strength.12 HMB supplementation may also help reduce muscle damage in response to strength training. More research is needed to confirm the effects, if any, of HMB supplementation on strength training and to determine the long-term safety of supplementation.

Dietary supplements that do not perform as claimed Most of the dietary supplements promoted as ergogenic aids fall into the category of ‘those that do not perform as claimed’. One example, carnitine, is discussed here; others include boron, chromium picolinate, coenzyme Q10, ginseng and pyruvate. In the body, carnitine facilitates the transfer of fatty acids across the mitochondrial membrane. Supplement manufacturers suggest that with more carnitine available, fat oxidation will be enhanced, but this does not seem to be the case. Carnitine supplements neither raise

muscle carnitine concentrations nor enhance exercise performance. Milk and meat products are good sources of carnitine, and supplements are not needed.

Dangerous, banned or illegal supplements The dietary supplements discussed thus far may or may not help athletic performance, but in the doses commonly taken, they seem to cause little harm. In contrast, some hormonal preparations are clearly damaging – anabolic steroids, DHEA (dehydroepiandrosterone), androstenedione, and hGH (human growth hormone). All of these ergogenic aids are dangerous to use and are banned by most professional sports leagues and the World Anti-Doping Agency established by the International Olympic Committee.

Anabolic steroids Among the most dangerous and illegal ergogenic practices is the taking of anabolic steroids. These drugs are derived from the male sex hormone testosterone, which promotes the development of male characteristics and lean body mass. The athletes who take steroids do so to stimulate muscle bulking. The known toxic side effects of steroids include, but are not limited to, extreme aggression and hostility, heart disease and liver damage. Taking these drugs is a form of cheating. The International Olympic Committee and almost all sporting agencies and governing organisations specifically ban the use of anabolic steroids. These authorities cite the known toxic side effects and maintain that taking these drugs is a form of cheating. Other athletes are put in the difficult position of either conceding an unfair advantage to competitors who use steroids or taking them and accepting the risk of harmful side effects. Young athletes should not be forced to make such a choice. The price for the potential competitive edge that steroids confer is high – sometimes it is life itself. Steroids are not simple pills that build bigger muscles. They are complex chemicals to which the body reacts in many ways, particularly when body builders and other athletes take large amounts. The safest, most effective way to build muscle has always been through hard training and a sound diet, and – despite popular misconceptions – it still is. Some manufacturers peddle specific herbs as legal substitutes for steroid drugs. They falsely claim that these herbs contain hormones, enhance the body’s hormonal activity, or both. In some cases, a herb may contain plant sterols, such as gamma-oryzanol, but these compounds are poorly absorbed. Even if absorption occurs, the body cannot convert herbal

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compounds to anabolic steroids. None of these products exhibits any proven anabolic steroid activity; none enhances muscle strength and some contain natural toxins. In short, ‘natural’ does not mean ‘harmless’.

DHEA and androstenedione

Some athletes use DHEA (dehydroepiandrosterone) and androstenedione as alternatives to anabolic steroids. DHEA and androstenedione are hormones made in the adrenal glands that serve as precursors to the male hormone testosterone. Advertisements claim the hormones ‘burn fat’, ‘build muscle’ and ‘slow ageing’, but evidence to support such claims is lacking. Short-term side effects of DHEA and androstenedione may include oily skin, acne, body hair growth, liver enlargement, testicular shrinkage and aggressive behaviour. Long-term effects, such as serious liver damage, may take years to become evident. The potential for harm from DHEA and androstenedione supplements is great, and athletes, as well as others, should avoid them.

Human growth hormone A wide range of athletes, including weightlifters, cyclists, and track and field participants use hGH (human growth hormone) to build lean tissue and improve athletic performance. These athletes use hGH, believing the injectable hormone will provide the benefits of anabolic steroids without the dangerous side effects. Taken in large quantities, hGH causes the disease acromegaly, in which the body becomes huge and the organs and bones over-enlarge. Other effects include diabetes, thyroid disorder, heart disease, menstrual irregularities, diminished sexual desire and shortened life span. The International Olympic Committee, the Australian Sports Anti-Doping Authority and most professional sports leagues ban hGH use, but its use is difficult to detect.

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A final word of caution It can be difficult to distinguish valid claims from bogus ones. Fitness magazines and websites are particularly troublesome because many of them present both valid and invalid nutrition information along with slick advertisements for nutrition products. Advertisements often feature colourful anatomical figures, graphs and tables that appear scientific. Some ads even include references, citing or linking to such credible sources. These ads create the illusion of endorsement and credibility to gain readers’ trust. Keep in mind, however, that the ads are created not to teach, but to sell. A careful reading of the cited research might reveal that the ads have presented the research findings out of context. For example, an ad might use a research article to conclude that its hGH supplement ‘increases lean body mass and bone mineral’ when, in fact, the researchers would conclude that ‘its general use now or in the immediate future is not justified’. Scientific facts are often exaggerated and twisted to promote sales. Highlight 1 describes ways to recognise misinformation and quackery. The search for a single food, nutrient, drug or technique that will safely and effectively enhance athletic performance will no doubt continue as long as people strive to achieve excellence in sports. When athletic performance does improve after use of an ergogenic aid, the improvement can often be attributed to the placebo effect, which is strongly at work in athletes. If a reliable source reports a performance boost from a newly tried product, give the effect time to fade away. Chances are excellent that it simply reflects the power of the mind over the body. The overwhelming majority of performance-enhancing aids sold for athletes are not effective. Wishful thinking will not substitute for talent, hard training, adequate diet and mental preparedness in competition. But don’t discount the power of mind over body for a minute – it is formidable, and sports psychologists dedicate their work to harnessing it. You can use it by imagining yourself a winner and visualising yourself excelling in your sport. You don’t have to buy magic to obtain a winning edge; you already possess it – your physically fit mind and body.

HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1 2

What are the moral implications of using ergogenic aids? Because of serious doping violations, Lance Armstrong was stripped of his seven Tour de France titles and banned from cycling for life. For him, these actions are ‘equivalent to a death sentence’. What

is your opinion of Armstrong’s doping violations and the imposed consequences? If you were a member of world cycling’s governing body, how would you propose determining which, if any, substances to allow and/or ban?

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NUTRITION ON THE NET Find out more information online. • Review the latest scientific evidence on supplements and sports nutrition at the nutrition page of the Australian Institute of Sport website: https://www.ais. gov.au/nutrition

•

Review fact sheets on sports supplements at the Sports Dietitians Australia website https://www. sportsdietitians.com.au/factsheets

REFERENCES CHAPTER 1

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W. E. Kraus and co-authors, Physical activity, all-cause and cardiovascular mortality, and cardiovascular disease, Medicine and Science in Sports and Exercise 51 (2019): 1270–1281; U. Ekelund and co-authors, Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women, Lancet 388 (2016): 1302–1310. Australian Bureau of Statistics, National Health Survey: First Results, 2017–18, ABS Cat. No. 4364.0.55.001, Canberra: ABS (2018); New Zealand Ministry of Health, New Health Survey 2019/2020, available at https://www.health.govt.nz/your-health/healthy-living/foodactivity-and-sleep/physical-activity/activity-levels-new-zealand J. H. Lee and H. S. Jun, Role of myokines in regulating skeletal muscle mass and function, Frontiers in Physiology 10 (2019): 42 Department of Health, Australia’s Physical Activity and Sedentary Behaviour Guidelines for Adults (2019). Available at https://www1. health.gov.au/internet/main/publishing.nsf/Content/healthpubhlth-strateg-phys-act-guidelines New Zealand Ministry of Health, Eating and Activity Guidelines. Available at https://www.health.govt.nz/our-work/eating-andactivity-guidelines American College of Sports Medicine, Position stand: Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: Guidance for prescribing exercise, Medicine and Science in Sports and Exercise 43 (2011): 1334–1359. X. Lin and co-authors, Leisure time physical activity and cardio-metabolic health: Results from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil), Journal of the American Heart Association 5 (2016): 6. N. M. Johannsen and co-authors, Combined aerobic resistance training effects on glucose homeostasis, fitness, and other major health indices: A review of current guidelines, Sports Medicine 46 (2016): 1809–1818. L. Dipietro and co-authors, Physical activity, injurious falls, and physical function in aging: An umbrella review, Medicine and Science in Sports and Exercise 51 (2019): 1303–1313. American College of Sports Medicine, Position stand: Progression models in resistance training for healthy adults, Medicine and Science in Sports and Exercise 41 (2009): 687–708. J. Bergstrom and co-authors, Diet, muscle glycogen and physical performance, Acta Physiologica Scandinavica 71 (1967): 140–150. B. S. Ferguson and co-authors, Lactate metabolism: Historical context, prior misinterpretations, and current understanding, European Journal of Applied Physiology 118 (2018): 691–728. M. Jensen and co-authors, Effect of carbohydrate mouth rinse on performance after prolonged submaximal cycling, Medicine and Science in Sports and Exercise 50 (2018): 1031–1038. D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and

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the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–528. D. Finger and co-authors, Ingestion of carbohydrate or carbohydrate plus protein does not enhance performance during endurance exercise: A randomized cross-over placebo-controlled clinical trial, Applied Physiology, Nutrition and Metabolism 43 (2018): 937–944. C. A. Burdon and co-authors, Effect of glycemic index of a preexercise meal on endurance exercise performance: A systematic review and meta-analysis, Sports Medicine 47 (2017): 1087–1101. D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–528. A. M. Fritzen, A. M. Lundsgaard, and B. Keins, Dietary fuels in athletic performance, Annual Review of Nutrition 39 (2019): 45–73. D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–528. R. B. Parks, S. J. Hetzel and M. Alison Brooks, Iron deficiency and anemia among collegiate athletes: A retrospective chart review, Medicine and Science in Sports and Exercise 49 (2017): 1711–1715; G. Bruinvels and co-authors, The prevalence and impact of heavy menstrual bleeding (menorrhagia) in elite and non-elite athletes, PLoS One 11 (2016): e0149881. R. B. Parks, S. J. Hetzel and M. Alison Brooks, Iron deficiency and anemia among collegiate athletes: A retrospective chart review, Medicine and Science in Sports and Exercise 49 (2017): 1711–1715. D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–528. B. P. McDermott and co-authors, National Athletic Trainers’ Association position statement: Fluid replacement for the physically active, Journal of Athletic Training 52 (2017): 677–695. D. T. Thomas, K. A. Erdman and L. M. Burke, Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–528. J. P. Higgins and co-authors, Energy drinks: A Contemporary Issues Paper, Current Sports Medicine Reports, 17 (2018): 65–72. M. E. Baker and co-authors, Short-term Mediterranean diet improves endurance exercise performance: a randomized-sequence crossover trial, Journal of the American College of Nutrition 38 (2019): 597–605.

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Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–528. N. M. Mathews, Prohibited contaminants in dietary supplements, Sports Health 10 (2018): 19–30. N. S. Guest and co-authors, International society of sports nutrition position stand: Caffeine and exercise performance, Journal of the International Society of Sports Nutrition 18 (2021): 1. S. A. Shah and co-authors, Impact of high-volume energy drink consumption on electrocardiographic and blood pressure parameters: A randomized trial, Journal of the American Heart Association 8 (2019): e011318. R. B. Kreider and co-authors, International Society of Sports Nutrition position stand: Safety and efficacy of creatine supplementation in exercise, sport, and medicine, Journal of the International Society of Sports Nutrition 14 (2017): 18. C. M. Kerksick and co-authors, ISSN exercise and sports nutrition review update: Research and recommendations, Journal of the International Society of Sports Nutrition 15 (2018): 38.

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R. J. Maughan and co-authors, IOC consensus statement: dietary supplements and the high-performance athlete, British Journal of Sports Medicine 52 (2018): 439–455. G. M. P. Brisola and A. M. Zagatto, Ergogenic effects of beta-alanine supplementation on different sports modalities: Strong evidence or only incipient findings? Journal of Strength and Conditioning Research 33 (2019): 253–282. A. N. Varanoske and co-authors, Comparison of sustained-release and rapid-release beta-alanine formulations on changes in skeletal muscle carnosine and histidine content and isometric performance following a muscle-damaging protocol, Amino Acids 51 (2019): 49–60. A. M. Jones and co-authors, Dietary nitrate and physical performance, Annual Review of Nutrition 38 (2018): 303–328. H. O. Campos and co-authors, Nitrate supplementation improves physical performance specifically in non-athletes during prolonged open-ended tests: A systematic review and meta-analysis, British Journal of Nutrition 119 (2018): 636–657. C. M. Kerksick and co-authors, ISSN exercise and sports nutrition review update: Research and recommendations, Journal of the International Society of Sports Nutrition 15 (2018): 38.

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15

LIFE CYCLE NUTRITION: PREGNANCY AND LACTATION Nutrition in your life

Food choices have consequences. Sometimes they happen immediately, such as heartburn after eating some pizza with extra chilli; other times, the consequences can sneak up on you, as when you gain a few extra kilos after repeatedly overindulging in double-chocolate milkshakes. Quite often, the consequences are temporary and easily resolved, as when hunger pangs strike after you drink only a diet soft drink for lunch. During pregnancy, however, the consequences of a woman’s food choices are dramatic. They affect not just her health, but also the growth and development of another human being – and not just for today, but for years to come. Making smart food choices is a huge responsibility, but, fortunately, it’s reasonably simple. PUTTING COMMON SENSE TO THE TEST Circle your answer

T F Being either underweight or overweight is associated with infertility. T F The neural tube development of a foetus occurs between 17- and 30-days gestation. T F The total folate requirement during pregnancy is 1000 micrograms (1 mg)/day. T F Birth weight is the most reliable indicator of an infant’s health. T F The recommended weight gain for a woman who begins pregnancy overweight and is

carrying a single foetus is 11.5 to 16 kilograms.

LEARNING OBJECTIVES 15.1 List the ways men and women can prepare for a healthy pregnancy.

15.2 Describe foetal development from conception to birth and explain how maternal malnutrition can affect critical periods. The unsaturated fats supplied by avocado are recommended as part of a balanced diet to help manage cholesterol

Chapter 15: Life cycle nutrition: pregnancy and lactation

15.3 Explain how being either underweight or overweight can interfere with a healthy pregnancy and how weight gain and physical activity can support maternal health and infant growth. 15.4 Summarise the nutrient needs of women during pregnancy.

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15.5 Identify factors predicting low-risk and high-risk pregnancies and describe ways to manage them. 15.6 Summarise the nutrient needs of women during lactation. 15.7 Explain how drinking alcohol endangers the foetus and how women can prevent foetal alcohol syndrome.

All people, be they pregnant and lactating women, infants, children, adolescents or adults, need the same nutrients, but the amounts they need vary depending on their stage of life. This chapter focuses on nutrition in preparation for, and support of, pregnancy and lactation. The next two chapters address the needs of infants, children, adolescents and older adults.

15.1  Nutrition prior to pregnancy

A section on nutrition prior to pregnancy must, by its nature, focus mainly on women. Both a man’s and a woman’s nutrition may affect fertility and possibly the genetic contributions they make to their children, but it is the woman’s nutrition that has the most direct influence on the developing foetus. Her body provides the environment for the growth and development of a new human being. Prior to pregnancy, a woman has a unique opportunity to prepare herself physically, mentally and emotionally for the many changes to come. In preparation for a healthy pregnancy, a woman can establish the following habits: • Achieve and maintain a healthy body weight – both underweight and overweight are associated with infertility.1 Overweight and obese men have low sperm counts and hormonal changes that reduce fertility.2 Excess body fat in women disrupts menstrual regularity and ovarian hormone production. Should a pregnancy occur, mothers, both underweight and overweight, and their newborns, face increased risks of complications. • Choose an adequate and balanced diet – malnutrition reduces fertility and impairs the early development of an infant should a woman become pregnant. • Be physically active – a woman who wants to be physically active when she is pregnant needs to become physically active beforehand. • Receive regular medical care – regular healthcare visits can help ensure a healthy start to pregnancy. • Manage chronic conditions – diseases such as diabetes, HIV/AIDS, phenylketonuria (PKU) and sexually transmitted infections can adversely affect a pregnancy and need close medical attention to help ensure a healthy outcome. • Avoid harmful influences – both maternal and paternal ingestion of harmful substances (e.g. cigarettes, alcohol, drugs, or environmental contaminants) can cause abnormalities, alter genes or their expression, and interfere with fertility.3 See Highlight 15 for the effects of excessive alcohol consumption during pregnancy. Young adults who nourish and protect their bodies do so not only for their own sake but also for future generations.

Being either underweight or overweight is associated with infertility. TRUE

AUSTRALIAN DIETARY GUIDELINES 2013 ---------------

REVIEW IT

Prior to pregnancy, the health and behaviours of both men and women can influence fertility and foetal development. In preparation, they can achieve and maintain a healthy body weight, choose an adequate and balanced diet, be physically active, receive regular medical care, manage chronic diseases, and avoid harmful influences.

PUTTING COMMON SENSE TO THE TEST

To meet additional energy needs, extra serves from the five food groups or unsaturated spreads and oils, or discretionary choices may be needed only by those women who are taller or more active but not overweight.

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15.2  Growth and development during pregnancy

A whole new life begins at conception. Organ systems develop rapidly, and nutrition plays many supportive roles. This section describes placental development and foetal growth, paying close attention to times of intense developmental activity.

Placental development In the early days of pregnancy, a spongy structure known as the placenta develops in the uterus. Two associated structures also form (see Figure 15.1). One is the amniotic sac, a fluid-filled balloon-like structure that houses the developing foetus. The other is the umbilical cord, a rope-like structure containing foetal blood vessels that extends through the foetus’s umbilicus to the placenta. These three structures (placenta, amniotic sac and umbilical cord) play crucial roles during pregnancy and are then expelled from the uterus during childbirth. The placenta develops as an interweaving of foetal and maternal blood vessels embedded in the uterine wall. The maternal blood transfers oxygen and nutrients to the foetus’s blood and receives foetal waste products. By exchanging oxygen, nutrients and waste products, the placenta performs the respiratory, absorptive, and excretory functions that the foetus’s lungs, digestive system and kidneys will provide after birth. The placenta is a versatile, metabolically active organ. Like all body tissues, the placenta uses energy and nutrients to support its work. Like a gland, it produces an array of hormones that maintain pregnancy and prepare the mother’s breasts for lactation. A healthy placenta is essential for the developing foetus to attain its full potential.

FIGURE 15.1   The placenta and associated structures To understand how placental villi absorb nutrients without maternal and foetal blood interacting directly, think of how the intestinal villi work. The GI side of the intestinal villi is bathed in a nutrientrich fluid (chyme). The intestinal villi absorb the nutrient molecules and release them into the body via capillaries. Similarly, the maternal side of the placental villi is bathed in nutrient-rich maternal blood. The placental villi absorb the nutrient molecules and release them to the foetus via foetal capillaries. Placenta

Umbilical cord

Amniotic fluid

Pool of maternal blood Placental villi extend into the pool of maternal blood Uterine tissue Maternal arteries bring fresh blood with oxygen and nutrients to the foetus Maternal veins carry foetal wastes away Foetal blood vessels within placental villi

Umbilical Umbilical vein artery

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3 A foetus after 11 weeks of development is just over 2.5 centimetres long. Notice the umbilical cord and blood vessels connecting the foetus with the placenta.

2 After implantation, the placenta develops and begins to provide nourishment to the developing embryo. An embryo 5 weeks after fertilisation is about 1.25 centimetres long.

4 A newborn infant after 9 months of development measures close to 50 centimetres in length. From 8 weeks to term, this infant grew 20 times longer and 50 times heavier.

Science Source/Petit Format/Nestle  

Foetal growth and development Foetal development begins with the fertilisation of an ovum by a sperm. Three stages follow: zygotic, embryonic and foetal (see Figure 15.2).

The zygotic stage

FIGURE 15.3   The concept of critical periods in foetal development Critical periods occur early in foetal development. An adverse influence experienced early in pregnancy can have a much more severe and prolonged impact than one experienced later.

The newly fertilised ovum, or zygote, begins as a single cell and divides to become many cells during the days after fertilisation. Within 2 weeks, the zygote embeds itself in the uterine wall – a process known as implantation. Cell division continues as each set of cells divides into many other cells. As development proceeds, the zygote becomes an embryo.

An adverse influence experienced late temporarily impairs development, but a full recovery is possible.

The embryonic stage

The embryo develops at an amazing rate. The number of cells in the embryo doubles approximately every 24 hours until the rate slows. At 8 weeks, the 1.6-centimetre embryo has a complete central nervous system, a beating heart, a digestive system, well-defined fingers and toes, and the beginnings of facial features, and is known as a foetus.

Normal development

The foetal stage

Critical periods Times of intense development and rapid cell division are called critical periods – critical in the sense that those cellular activities can occur only

An adverse influence experienced early permanently impairs development, and a full recovery never occurs.

Growth

The foetus continues to grow during the next seven months. Each organ grows to maturity according to its own schedule, with greater intensity at some points than at others. As Figure 15.2 shows, foetal growth is phenomenal – weight increases from less than 30 grams to about 3.4 kilograms at birth. Most successful pregnancies last 38 to 42 weeks and produce a healthy infant weighing between 2.5 and 3.8 kilograms.

Cindy Vannelli              Science Source/Petit Format/Nestle

1 A newly fertilised ovum is called a zygote and is about the size of a full stop at the end of this sentence. Less than one week after fertilisation, these cells have rapidly divided multiple times to become a blastocyst ready for implantation.

 

Science Source/Petit Format/Nestle

FIGURE 15.2   Stages of embryonic and foetal development

Critical period

Time

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FIGURE 15.4   Critical periods of development During embryonic development (from 2 to 8 weeks), many of the tissues are in their critical periods (purple area of the bars); events that occur will have irreversible effects on the development of those tissues. In the later stages of development, the tissues continue to grow and change, but the events are less critical in that they are relatively minor or reversible. Central nervous system Heart Ears

Tissue

Eyes Legs and arms Teeth Palate External genitalia

0

2

4 Embryo

8

12

16

Term

Foetus Weeks of gestation

Adapted from Before We Are Born: Essentials of Embryology and Birth Defects by K. L. Moore and T.V.N. Persaud (W. B. Saunders, 2003).

The neural tube is the structure that eventually becomes the brain and spinal cord.

at those times. If cell division and number are limited during a critical period, full recovery is not possible (see Figure 15.3). The development of each organ and tissue is most vulnerable to adverse influences (e.g. nutrient deficiencies or toxins) during its own critical period (see Figure 15.4). The critical period for neural tube development, for example, is from 17 to 30 days gestation. Consequently, neural tube development is most vulnerable to nutrient deficiencies, nutrient excesses or toxins during this critical time – a time when many women do not even realise they are pregnant. Any abnormal development of the neural tube or its failure to close completely can cause a major defect in the central nervous system. Figure 15.5 shows photos of neural tube development in the early weeks of gestation.

FIGURE 15.5   Neural tube development

The neural tube development of a foetus occurs between 17- and 30-days gestation. TRUE

Science Photo Library/Edelmann

PUTTING COMMON SENSE TO THE TEST

Science Photo Library/Steve Gschmeissner

The neural tube is the beginning structure of the brain and spinal cord. Any failure of the neural tube to close or to develop normally results in central nervous system disorders, such as spina bifida and anencephaly. Successful development of the neural tube depends, in part, on the vitamin folate.

At 4 weeks, the neural tube has yet to close (notice the gap at the top).

At 6 weeks, the neural tube (outlined by the delicate red vertebral arteries) has successfully closed.

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Neural tube defects In Australia (excluding the Northern Territory) and New Zealand, approximately 45 to 50 of every 100 000 newborns are born with a neural tube defect; roughly 108 or so infants are affected each year, and worldwide, the annual rate is approximately 300 000 to 400 000.4 Many other pregnancies with neural tube defects end in abortions or stillbirths. The two most common types of neural tube defects are anencephaly and spina bifida. In anencephaly, the upper end of the neural tube fails to close. Consequently, the brain is either missing or fails to develop. Pregnancies affected by anencephaly often end in miscarriage; infants born with anencephaly die shortly after birth. Spina bifida is characterised by incomplete closure of the spinal cord and its bony encasement (see Figure 15.6). The meninges membranes covering the spinal cord often protrude as a sac, which may rupture and lead to meningitis, a life-threatening infection. Spina bifida is accompanied by varying degrees of paralysis, depending on the extent of the spinal cord damage. Mild cases may not even be noticed, but severe cases often lead to death. Common problems include club foot, dislocated hip, kidney disorders, curvature of the spine, muscle weakness, mental handicaps, and motor and sensory losses. The cause of neural tube defects is unknown, but researchers are examining several gene–gene, gene–nutrient and gene–environment interactions. A pregnancy affected by a neural tube defect can occur in any woman, but factors that make it more likely are:5 • a previous pregnancy affected by a neural tube defect • maternal diabetes (type 1) • maternal use of anti-seizure medications • maternal obesity • exposure to high temperatures early in pregnancy (prolonged fever or hot-tub use)

Reminder: A neural tube defect is a malformation of the brain, spinal cord or both during embryonic development. The two main types of neural tube defects are spina bifida (literally, ‘split spine’) and anencephaly (‘no brain’)

FIGURE 15.6   Spina bifida Spina bifida, the most common neural tube defect, occurs when the vertebrae of the spine fail to close around the spinal cord, leaving it unprotected. The B vitamin folate helps prevent spina bifida and other neural tube defects.

SPINA BIFIDA

Vertebra

NORMAL SPINE

Meninges Spinal cord Spinal fluid

Spine

Spine

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• race/ethnicity (more common among Anglo-Saxons than others) • low socioeconomic status. Folate supplementation reduces the risk.

Folate supplementation

Folate RDI (from dietary intake only): • for women: 400 µg (0.4 mg)/day • during pregnancy: 600 µg (0.6 mg)/ day.

PUTTING COMMON SENSE TO THE TEST

The total folate requirement during pregnancy is 1000 micrograms (1 mg)/ day. TRUE

Chapter 10 described how folate supplements taken one month before conception and continued throughout the first trimester can help support a healthy pregnancy, prevent neural tube defects, and reduce the severity of those that do occur. For this reason, all women planning pregnancy, or of child-bearing age should consume an additional 400 micrograms (0.4 mg) of folate daily beyond the Recommended Daily Intake (RDI) of 400 micrograms. During pregnancy, the RDI for folate is 600 micrograms. This means that during the first trimester of pregnancy, total intake, including supplements, should be approximately 1000 micrograms (dietary intake of 600 mg plus 400 mg as a supplement). In the second and third trimesters of pregnancy, women should continue to maintain an adequate folate intake and aim for the RDI for pregnancy of 600 micrograms. Because high doses of folate can mask the symptoms of pernicious anaemia associated with vitamin B12 deficiency, caution should be applied if taking higher than recommended doses of folate. Note that prenatal supplements contain varying amounts of folate per dose. The Nutrient Reference Values for Australia and New Zealand (NRVs) indicate that the RDI for pregnant women for folate is 600 micrograms per day, but this does not take into consideration the additional supplemental folic acid required to prevent neural tube defects. Because approximately half of pregnancies each year are unplanned and because neural tube defects occur early in development before most women realise they are pregnant, bread flour in Australia is fortified with folate to help ensure an adequate intake. Labels on products containing additional folate may claim that an ‘adequate intake of folate has been shown to reduce the risk of neural tube defects’. In New Zealand, a voluntary fortification standard exists for fortifying up to 50 per cent of packaged sliced bread. The Ministry for Primary Industries in New Zealand decided in July of 2021 to mandate the fortification of folic acid in non-organic wheat flour used for bread-making.6

CURRENT RESEARCH IN NUTRITION Folic acid in pregnancy A lack of folic acid early in pregnancy is known to cause neural tube defects, such as spina bifida, but recent research shows a strong association between maternal folic acid intake and the risk of a baby developing cleft lip and cleft palate. The risk of having a cleft lip or palate appears to be more than four times higher if mothers do not take folic acid in the first three months of pregnancy than if they do take folic acid in the first three months.7

Chronic diseases Much research suggests that adverse influences at critical times during foetal development set the stage for the infant to develop chronic diseases in adult life. Poor maternal diet during critical periods may permanently alter body functions that influence disease development, such as blood pressure, glucose tolerance and immune functions. For example, maternal diet may alter blood vessel growth and program lipid metabolism and lean body mass development in such a way that the infant will develop risk factors for cardiovascular disease as an adult. Malnutrition during the critical period of pancreatic cell growth provides an example of how type 2 diabetes may develop in adulthood.8 The pancreatic cells responsible for producing insulin (the beta cells) normally increase more than 130-fold between 12 weeks gestation and five months after birth. Nutrition is a primary determinant of beta cell growth, and infants who have suffered prenatal malnutrition have significantly fewer beta cells than well nourished infants. They are also more likely to be low-birth-weight infants – low birth weight and premature birth correlate with insulin resistance and type 2 diabetes later in

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life. One hypothesis suggests that diabetes may develop from the interaction of inadequate nutrition early in life with abundant nutrition later in life, whereby the small mass of beta cells developed in times of undernutrition during foetal development may be insufficient in times of over-nutrition during adulthood when the body needs more insulin. Hypertension may develop from a similar scenario of inadequate growth during placental and gestational development followed by accelerated growth during early childhood: the small mass of kidney cells developed during malnutrition may be insufficient to handle the excessive demands of later life. Low-birth-weight infants who gain weight rapidly as young children are likely to develop hypertension and heart disease as adults.

Foetal programming Recent genetic research may help to explain the phenomenon of substances, such as nutrients, influencing the development of diseases later in adulthood – a process known as foetal programming. In the case of pregnancy, the mother’s nutrition can permanently change gene expression in the foetus with some research suggesting that foetal programming may influence several succeeding generations.9 Because critical periods occur throughout pregnancy, a woman should continuously take good care of her health. That care should include achieving and maintaining a healthy body weight prior to pregnancy and gaining sufficient weight during pregnancy to support a healthy infant. REVIEW IT

Maternal nutrition before and during pregnancy affects both the mother’s health and the infant’s growth. As the infant develops through its three stages – zygotic, embryonic and foetal – its organs and tissues grow, each on their own schedule. Times of intense development are critical periods that depend on supply of nutrients to proceed smoothly. Without folate, for example, the neural tube fails to develop completely during the first month of pregnancy, prompting recommendations that all women of child-bearing age take folate daily.

15.3  Maternal weight

Birth weight is the most reliable indicator of an infant’s health. An underweight infant is more likely to have physical and mental defects, become ill or die than a normal-weight infant. In general, higher birth weights present fewer risks for infants. Two characteristics of the mother’s weight influence an infant’s birth weight: her weight prior to conception and her weight gain during pregnancy.

Weight prior to conception A woman’s weight prior to conception influences foetal growth. Even with the same weight gain during pregnancy, underweight women tend to have smaller babies than heavier women.

Underweight An underweight woman has a high risk of having a low-birth-weight infant, especially if she is malnourished or unable to gain sufficient weight during pregnancy. In addition, the rates of preterm births and infant deaths are higher for underweight women. An underweight woman improves her chances of having a healthy infant by gaining sufficient weight prior to conception or by gaining extra kilograms during pregnancy. To gain weight and ensure nutrient adequacy, an underweight woman can follow the dietary recommendations for pregnant women (described in Section 15.4).

Overweight and obesity An estimated one-third of all pregnant women in Australia and New Zealand are overweight or obese, which can create problems related to pregnancy and childbirth.10 Obese women have

BMI was introduced in Chapter 8. • underweight = BMI