Dietary Supplements and Functional Foods E-Book

Geoffrey P. Webb

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 710

Veröffentlichungsjahr: 2011

Beschreibung

The study of nutritional supplements has become increasingly important within research establishments and universities throughout the world, and as the market for these products continues to grow, so does the need for comprehensive scientifically sound information about the products, their properties and potential health benefits.

This second edition of Dietary Supplements & Functional Foods has been fully revised and expanded. The book looks at the accepted uses of dietary supplements and also explores the wider picture, identifying common themes and principles or particular categories of supplements. Much new information across the whole spectrum of this fascinating and expanding field is included, with additional material covering changes in relevant legislation, examples of superfoods, up-to-date information and informed debate concerning vitamin D, folic acid, fish oils and antioxidants Several new sections have been added to this successful and well-received book. This book is now even more user-friendly and ideal for course use, and an invaluable reference for those working in the health sciences, and the supplements industry. Dietitians, nutritionists, food scientists and food technologists will all find much of great use and value within its covers. All universities and research establishments where these subjects are studied and taught should have copies of this excellent new edition on their shelves.

Leseprobe

Contents

Preface

1 An Overview of Dietary Supplements and Functional Foods

The evolving rationale for supplement use

Adequacy and the prevention of deficiency diseases

Diet as a means to prevent chronic, age and wealth-related diseases

Supplements versus dietary change for the prevention of chronic disease

Dietary supplements and natural remedies as a safer alternative to modern medicine?

Defining dietary supplements

Legal regulation of dietary supplements (the UK and EU perspective)

Medicines

Non-medicinal supplements

Borderline products

Health claims

Vitamin and mineral supplements

Regulation in the USA

Supplement quality

The market for supplements

Reasons for taking supplements

To compensate for a perceived or potential inadequacy in the diet

To compensate for some perceived increase in need or defective handling of a nutrient

To treat or prevent non-deficiency diseases

To improve athletic performance

Do supplements and functional foods work? Testing their effectiveness and safety

Measures of outcome

The two main investigative approaches

The observational approach

The experimental approach

Testing: A summing up

2 An Overview of Micronutrient Adequacy

Introduction and scope of the chapter

Judging the adequacy of micronutrient intakes

A note about American standards

Recommended daily allowances on food labels

Measuring an individual’s micronutrient status using clinical or biochemical observations

Micronutrient adequacy of the UK population

Young and middle-aged adults

Children

Pregnant women

Lactating women

The elderly

Athletes in training

Summing up

3 The Individual Vitamins

The fat-soluble vitamins

Vitamin A (retinol)

Vitamin D (cholecalciferol)

Vitamin E (α-tocopherol)

Vitamin K (phylloquinone)

The water-soluble vitamins

Vitamin B1(thiamin)

Vitamin B2(riboflavin)

Vitamin B3 (niacin)

Vitamin B6 (pyridoxine)

Vitamin B12 (cobalamins)

Folic acid (folate, folacin)

Biotin

Pantothenic acid

Vitamin C (ascorbic acid)

4 The Minerals

Calcium

Chromium

Copper

Fluoride

Iodine

Iron

Magnesium

Manganese

Molybdenum

Potassium

Selenium

Zinc

5 Free Radicals and Antioxidants

Introduction

The free radical or oxidant theory of disease

Mechanisms for limiting free radical damage

Diets with plentiful supplies of (antioxidant-rich) fruits and vegetables are associated with a reduced risk of chronic diseases

What evidence is there that antioxidant supplements are beneficial or at least harmless?

Antioxidants and pre-eclampsia in pregnancy

Vitamin E and dementia

Summing up the case for antioxidant supplements

6 Natural Fats and Oils

The nature of fats, oils and other lipids

Why are we preoccupied with the balance of our dietary fats?

Why are some fatty acids called ‘essential’?

Essential fatty acids and eicosanoid production

Fish oil supplements

What are the suggested benefits of taking fish (liver) oil supplements?

Fish oil supplements and heart disease: Evidence of effectiveness

Evidence relating fish oils to inflammatory conditions such as arthritis

Fish oils, brain and behaviour

Evening primrose oil and other sources of GLA

Flaxseed oil

Conjugated linoleic acid (CLA)

β-sitosterol and the phytosterols

7 Non-Essential ‘Nutrients’ that are Used as Dietary Supplements

General rationale

Glucosamine and chondroitin sulphate

Nature and functions of cartilage

Supplement forms and origins

Rationale for use and evidence of effectiveness

s-Adenosyl-methionine (SAMe)

Nature and functions

Rationale for use and evidence of efficacy

Lecithin and choline

L-carnitine

Nature and synthesis of L-carnitine

Functions of carnitine

Circumstances that may increase carnitine requirements

Use of carnitine supplements

Carnitine supplements: Conclusions

Creatine

Nature and origins of body creatine

Functions of creatine

Rationale and evidence for the use of creatine supplements

Coenzyme Q10 (ubiquinone)

Nature and sources of coenzyme Q10

Functions of coenzyme Q10

Rationale and evidence for the use of coenzyme Q10 supplements

Alpha(α)-lipoic acid

Nature and sources of body alpha-lipoic acid

Functions of alpha-lipoic acid

Rationale and evidence for the use of alpha-lipoic acid supplements

Methylsulphonylmethane (MSM)

Nature and sources of MSM

MSM as a supplement

8 Natural Products and Extracts

Scope of the chapter

Secondary plant metabolites

Terpenoids

Phenolic compounds (phenols and polyphenols)

Nitrogen-containing alkaloids

Sulphur-containing plant secondary metabolites

How might these secondary metabolites reduce the risk of chronic disease?

Natural extracts as a source of drugs

The individual plant and animal extracts

Agnus castus

Aloe vera

Bee products

Chitosan

Echinacea

Garlic

Ginger

Ginkgo biloba

Ginseng

Guarana

Kelp

Milk thistle

Saw palmetto

Spirulina and chlorella

St John’s wort (Hypericum perforatum)

Tea extracts

9 Functional Foods

Introduction and scope of the chapter

A note about ‘superfoods’

Phytosterols and phytostanols

Phyto-oestrogens

Probiotics, prebiotics and synbiotics

Definitions and scale of usage

The lactic acid bacteria

Breast milk and the ‘bifidus factor’

What makes a good probiotic?

Suggested benefits of probiotics

Effect of probiotics on incidence and severity of diarrhoea

Possible effects of probiotics on the risk of developing bowel cancer

Probiotics and the prevention of childhood eczema

Prebiotics

Synbiotics

References

Index

Dietary Supplementsand Functional Foods

This edition first published 2011© 2011 and 2006 Blackwell Publishing Ltd

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Library of Congress Cataloging-in-Publication Data

Webb, Geoffrey P.

Dietary supplements and functional foods / Geoffrey P. Webb. – 2nd ed.

p. ; cm.

Includes bibliographical references and index.

ISBN 978-1-4443-3240-7 (pbk. : alk. paper)1. Dietary supplements. 2. Functional foods. I. Title.

[DNLM: 1. Dietary Supplements. 2. Functional Food. QU 145.5]

RM258.5.W43 2011

615′.1–dc22

2010040968

A catalogue record for this book is available from the British Library.

Preface

In the preface to the first edition of this book, I stated that one of my major objectives was to give order and structure to the topic of dietary supplements and functional foods. Hundreds of substances are marketed as dietary supplements and so one approach would have been to select a number of the most popular substances, arrange them alphabetically and then discuss each of them separately, perhaps using a series of common subheadings. Mason (2007) had already used this approach in the first edition of her very useful reference book on supplements, so rather than produce a similar competing book, I tried to structure this book in the way one might organise the syllabus and teaching for an undergraduate module: emphasising common themes, logical groupings and general principles and concepts.

As with an undergraduate module, I have started with an overview of the topic: the types and uses of supplements, the extent of usage, potential hazards of taking supplements, the legal regulation of supplements and a thorough review of the sources of information and the scientific methods used to determine their effectiveness and safety. An understanding of the methodology used in their assessment is essential not only for thosE considering a research project in this area, but also to anyone who wants to read and evaluate the scientific literature.

The traditional motivation for using supplements was to ensure adequacy of essential micronutrients. In Chapter 2 there is an assessment of the extent to which one can assume adequacy in industrialised countries and the numbers and types of people for whom this assumption of adequacy would be misplaced. For non-nutritionists this chapter also includes an overview of how the adequacy of micronutrient intakes is defined and measured and how micronutrient status can be assessed.

Chapters 3, 4 and 6 deal with individual micronutrients, the vitamins and minerals, and also with natural oils that are sources of essential fatty acids. Since 2004, there has been a lot of published research relating to vitamin D. This research relates not only to its importance in maintaining bone health, but also to its effects outside of bone and emerging evidence linking low vitamin D status to conditions like diabetes, multiple sclerosis and hypertension; the expanded section on vitamin D reflects this new focus. When I wrote the first edition, I was confident that mandatory fortification of flour in the UK with folic acid was imminent; this has not happened and in Chapter 3, I discuss at length why the authorities have delayed introducing this measure. In the section on fish oils in Chapter 6, I include a new section dealing with claims that these supplements might affect mood, attention and behaviour, especially in children. Much media attention has been given to studies that claim to show benefits for fish oil supplements in schoolchildren, but my literature search suggests that there is almost no proper scientific research into this claim.

As in the first edition, Chapter 5 deals with antioxidants and the oxidant theory of disease. Although substances with antioxidant activity are in all categories of supplements, I took the decision in 2004 to deal with them together as a separate grouping. A large proportion of the news reports about the benefits of ‘superfoods’ and supplements relate to their antioxidant effects and there is a general assumption that antioxidants are good for us and that large intakes will help in preventing and treating disease; observational evidence also tends to support this view. However, I noted in the first edition that the evidence that large supplemental intakes actually confer long-term health benefits is not supported by the results of clinical trials, and that most of the supposed long-term benefits are extrapolated from short-term, reductionist studies. In 2004, I considered this scepticism to be a minority view, but in its consideration of ‘health claims’ for particular foods or ingredients, the European Food Standards Agency has recently given a negative opinion about antioxidant claims, because there is a lack of evidence of real physiological benefit associated with improvements in measures of oxidant stress or antioxidant status.

As in the first edition, Chapter 7 deals with a number of organic substances that are mostly natural metabolites with vitamin-like functions. These are not considered essential nutrients, because endogenous synthesis is thought to be sufficient to meet our physiological needs for them. The rationale for taking these substances as supplements is the belief that in some people or in some circumstances (for example disease) endogenous synthesis is not sufficient for optimal functioning, or that supplemental intakes may prevent or ameliorate disease.

Chapter 8 deals mainly with plant extracts that have been sold as food supplements. Although some of these substances are derived from accepted foods, others would be from plants that would not be recognised as mainstream foods in the UK. One major difficulty I have had in writing this new edition has been to decide if and how the EU Traditional Herbal Medicinal Products Directive might (in April 2011) affect the availability of these substances when sold over the counter as food supplements. My understanding from discussions with the FSA and the MHRA is that four of the substances singled out for discussion in this chapter (Agnus castus, Echinacea, milk thistle and St John’s wort) need to be sold as registered traditional medicines rather than as food supplements. It seems probable that extracts of these herbs will continue to be available for sale over the counter, but only those produced by authorised manufacturers will be available from sources within the EU. It is the bio-activity of secondary metabolites in these plant extracts that is the basis for believing that they might have beneficial effects when taken as supplements. There are many tens of thousands of these secondary metabolites but, in line with my objective of trying to give order and structure, I have made the point that they can be divided into a small number of categories of substances with common structural features, characteristics and synthetic origins within plants.

The final chapter deals with functional foods. The sales growth of functional foods is outstripping growth in the total food market and probably taking some market share from the food supplement market, which has been growing only slowly in recent years. The list of substances sold as supplements has grown and is expanding, so I considered adding extra substances to my list of extracts in Chapter 8. Many of these new supplements are extracts of ordinary or exotic foods that are claimed to have particularly high levels of particular nutrients or other substances like antioxidants, and these have been termed ‘superfoods’. All of the substances that I considered adding to my list of natural extracts are extracts of one of these superfoods and so, rather than discuss them individually, I have added a short section on superfoods to Chapter 9.

1An Overview of Dietary Supplements and Functional Foods

The evolving rationale for supplement use

Adequacy and the prevention of deficiency diseases

Traditionally, dietary supplements like cod liver oil, iron tablets and multivitamins were taken to ensure the adequacy of our diet: that it contained enough essential nutrients to prevent overt deficiency disease and that we did not suffer other, more subtle adverse effects of marginal nutrient inadequacy. While this remains an important motivation for many people, others now also take supplements in the hope that they will have additional health benefits, for example:

To reduce the risk of developing a chronic age-related disease such as cancer, heart disease, osteoporosis or type 2 diabetes.To compensate for some (perceived) individual idiosyncrasy that may increase the requirement for an accepted nutrient or make another substance an essential nutrient for that person.To ‘boost the immune system’.To treat or lessen the symptoms of a non-deficiency disease such as clinical depression or arthritis.To boost intake during periods of (perceived) increase in requirement, such as in pregnancy, illness or old age.To boost athletic performance.

One ironic consequence of these new circumstances is that the high levels of vitamin A and D in cod liver oil, the traditional reason for taking it, may actually be seen as a disadvantage. These vitamins are toxic in excess and may prevent us from safely taking large doses of the essential polyunsaturated fats that are now regarded as the most important active ingredients of fish and fish liver oils (see Chapter 6).

During the first half of the twentieth century it was found that certain foods and essential nutrients extracted from these foods could prevent or cure several common, serious and frequently fatal diseases, such as those listed below:

Vitamin C cures scurvy, a frequently fatal disease experienced by those undertaking long voyages by sail or expeditions where they were required to live for long periods without access to fruit or vegetables. It is characterised by bleeding gums, excessive bruising and a tendency to haemorrhage internally.Niacin (vitamin B3) cures pellagra, a fatal disease that is associated with a subsistence diet composed largely of maize. It is characterised by the ‘4 Ds’: diarrhoea, dermatitis, dementia and ultimately death.Thiamin (vitamin B1) cures beriberi, another potentially fatal disease that is associated with a diet heavily dependent on polished (white) rice. It is characterised by degeneration of sensory and motor nerves, loss of peripheral sensation, paralysis, brain damage, oedema and heart failure.Iodine supplements cure goitre and the iodine deficiency diseases, which are still endemic in many areas where the soil iodine content is low. They are characterised by low metabolic rate and mental deterioration in adults (myxoedema), severe and irreversible impairment of mental and physical development in children (cretinism), as well as high risk of miscarriage, stillbirth and birth defects.Vitamin D cures rickets, a disease once prevalent among children in the northern industrialised cities of Europe due to a combination of poor diet and low exposure of the skin to summer sunlight. Rickets leads to characteristic abnormalities in the skeleton like bow legs (which may not be entirely reversible), as well as poor growth, muscle weakness and high susceptibility to infection.Vitamin A prevents and ‘cures’ xerophthalmia, in which there is progressive deterioration of the eyes leading ultimately to permanent and irreversible blindness. Vitamin A deficiency also increases susceptibility to, and death from, infectious diseases. Deficiency occurs in populations subsisting largely on starchy foods who eat practically no animal fats and few green or brightly coloured fruits or vegetables.

Some of these diseases are still very prevalent in some parts of the world. Vitamin A deficiency causes hundreds of thousands of children in the Third World to go blind each year and is a major contributory factor in the high child and infant mortality seen in some countries. Iodine deficiency and goitre still affect hundreds of millions of people globally and iodine deficiency is the world’s most common preventable cause of mental deficiency in children.