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LIPIDS IN NUTRITION AND HEALTH: A REAPPRAISAL This electronic version was published by The Oily Press in 2009 and is available in PDF for download free of charge for personal use from the publisher's web site (www.oilypress.com). It is offered as a historical resource and represents the author's views at the time of writing, i.e. in the late1990s. The information should not be interpreted without reference to the many studies of lipids in nutrition and health carried out since 1999. The author and the publisher hope that the availability of this version in electronic format and free of charge will help spread a better understanding of the development of ideas on the role of lipids in nutrition and health. MICHAEL I. GURR 11 Books on fats, oils and other lipids PJ Barnes & Associates, PO Box 200, Bridgwater, TA7 0YZ, UK Tel: +44-1823-698973 E-mail: This electronic version was published by The Oily Press in 2009 and is available in PDF for download free of charge for personal use from the publisher's web site (www.oilypress.com). It is offered as a historical resource and represents the author's views at the time of writing, i.e. in the late1990s. The information should not be interpreted without reference to the many studies of lipids in nutrition and health carried out since 1999. LIPIDS IN NUTRITION AND HEALTH: A REAPPRAISAL Based upon a compilation of articles on lipids in nutrition written by the author and published in Lipid Technology 1989–98 Michael I. Gurr Maypole Scientific Services, Isles of Scilly, UK THE OILY PRESS BRIDGWATER Copyright © 1999, 2009 PJ Barnes & Associates iv Copyright © 1999 PJ Barnes & Associates PO Box 200, Bridgwater TA7 0YZ, England All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted by any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission in writing from the publisher. All reasonable care is taken in the compilation of information for this book. However, the author and publisher do not accept any responsibility for any claim for damages, consequential loss or loss of profits arising from the use of the information. ISBN 0-9531949-1-4 This book is Volume 11 in The Oily Press Lipid Library Publishers Note: This book is based upon a compilation of articles on lipids in nutrition written by the author and published in Lipid Technology. The book is written and published with full permission from the publisher of Lipid Technology. References are made to published scientific papers throughout this book but it was deemed unnecessary to give references to the original Lipid Technology articles upon which it is based. Copyright © 1999, 2009 PJ Barnes & Associates v Foreword For ten years, Mike Gurr has written his nutrition article in Lipid Technology, amounting in all to nearly 60 articles. These have always been well received and have been one of the attractive features of the magazine. He writes clearly and carefully and with a light touch so that even those who might oppose his conclusions recognise his underlying knowledge, his ability, and the power of his arguments. It has now been agreed that all these articles should be organized into a single summarizing volume where they can be presented systematically, revising and updating only where this is necessary. The result is a powerful and critical survey of important aspects of lipid nutrition which will be appreciated by Lipid Technology readers and should be compulsory reading for those not familiar with the original articles. It also represents a convenient presentation of material spread through almost 60 issues. Since 80% of the global production of oils and fats — now exceeding 100 million tonnes — is consumed as food and a further 6% is eaten by animals to produce more human food it is not surprising that nutrition is one of the active areas in lipid science. Older aspects of this field such as the effects of saturated acids continue to be investigated while new aspects like conjugated linoleic acid provide excitement. What are our dietary needs? How do lipids as a whole and lipids as individual compounds affect us in respect of health and disease? These are important questions which attract a lot of attention. Most commentators — whether they be review writers, government health committees, or contributors to newspapers or magazines — are recycling what others have written, generally without careful assessment of the original articles. We are told what has been discovered. All the caveats of the original authors have got lost, suggestions become facts, arguments are simplified, and possibilities become certainties which are repeated and re-presented until they are part of received wisdom and no longer questioned. Mike Gurr belongs to that small group of writers who is not content with second-hand opinion but goes back to the original papers, reads them Copyright © 1999, 2009 PJ Barnes & Associates vi carefully, and re-assesses the conclusions on the basis of his extensive knowledge of nutritional science. His conclusions are sometimes unexpected and do not always accord with the nostrum of the day. They are always thoughtful and merit careful consideration. There is a growing awareness that some of the early nutrition experiments were not of the best design, that conclusions sometimes went beyond the experimental evidence, that the lipid hypothesis for cardiovascular disease, for example, is far from the whole story, and that early conclusions about cholesterol and saturated acids need to be reconsidered. Lipid Technology is pleased to have contributed to the new thinking through Mike Gurr’s writing over 10 years and is proud to present this volume of collected revised papers in the belief that they will contribute powerfully to the on-going debate. Frank Gunstone Editor, Lipid Technology April 1999, Nether Rumgally Copyright © 1999, 2009 PJ Barnes & Associates vii Preface Between 1989 and 1998, I contributed regular articles to Lipid Technology on nutritional aspects of lipids. Together these provide a clear picture of the development of concepts in lipid nutrition during this time and highlight some important advances in research in six main areas: •Influence of dietary lipids on blood lipid and lipoprotein concentrations. •Dietary lipids and cardiovascular diseases. •Nutritional significance of lipid peroxidation. •Importance of polyunsaturated fatty acids in nutrition. •Dietary lipids and weight control. •Lipids in foods and raw materials. To provide coherent summaries for those interested in these topics, I have grouped together the Lipid Technology articles under these different headings, editing and updating where necessary. Some early articles have been omitted or considerably truncated where the material had become outdated and superseded by later articles. Many articles did not fall neatly into these topics. These have been edited into the text of different chapters to provide introductory or background material (e.g. digestion and assimilation of lipids, consideration of dietary reference values, lipids and cancer). In the chapter on ‘Lipids in foods and raw materials’ I have grouped together such topics as lipids in meat, milk, infant foods, palm, or lipids of special interest (e.g. plant sterols, short-chain and medium-chain fatty acids). For those who have not been regular readers of my Lipid Technology articles, I should point out that my interpretation of the scientific evidence for the significance of dietary lipids in the development of diseases such as heart disease, often differs considerably from those of my nutritionist colleagues. It certainly differs from the ‘consensus view’ adopted by most public health bodies. Shortly before putting pen to paper for one of my Lipid Technology articles, I was present at a meeting on new aspects of fats Copyright © 1999, 2009 PJ Barnes & Associates viii processing attended by people from the fats and oils industry. At dinner in the evening, my neighbour, by way of making conversation said “I enjoy your articles in Lipid Technology”. My face glowed with pleasure; everyone likes praise! He continued: “I particularly like their facetious style”. My face fell. My dictionary defines facetious as “characterized by flippant or inopportune humour”. It certainly has not been my intention to be flippant or that my articles have anything other than serious scientific intent, although I hope they also make enjoyable reading. It is quite intentional however, that many of these articles are imbued with a certain scepticism (sceptical: “inclined to question the truth or soundness of accepted opinions” — my dictionary again!). The reason for this is that nutrition is a discipline which, as well as being underpinned by several fundamental sciences such as chemistry and physiology, also has distinct sociological attributes since it impinges necessarily on all our lives. It is therefore a subject in which it is all too easy to stray away from strict scientific reasoning, a topic on which I have expounded in another journal (1). It has been my intention in these papers to examine critically the credentials of some popular beliefs about nutrition that have entered or are in danger of entering folklore, rather than to present bland and uncritical regurgitations of the literature. I have taken pains to try to point out why interpretations may differ so widely. I hope that these ‘collected works’ will provide a useful source of reference material on important lipid nutrition topics as well as being ‘a good read’. M.I.Gurr St Mary’s, April 1999 Reference 1. Gurr, M.I. (1994) Biologist, 41, 191–194. Copyright © 1999, 2009 PJ Barnes & Associates ix CONTENTS 1. Influence of Dietary Fats on the Concentrations of Lipids carried in the Blood and the Significance for Health ............ 1 Introduction .................................................................................. 3 Fat digestion and assimilation ...................................................... 3 The trouble with lipids 3 Early stages of lipid digestion 3 Digestion in the small intestine 5 Undigestible fats 6 Absorption of fat digestion products 6 Resynthesis of absorbed digestion products 7 Transport of fats in the blood 7 Prediction of lipid and lipoprotein responses to dietary fat and cholesterol .............................................................................. 8 Background 8 A new meta-analysis 9 Criteria for inclusion in the analysis 10 Predictive equations 10 Dietary cholesterol 11 Saturated fatty acids 12 Monounsaturated fatty acids 12 Polyunsaturated fatty acids 13 Total fat 13 Conclusions 13 Cholesterol in the diet and in the blood: a more detailed appraisal ........................................................................ 14 What is cholesterol? 14 Where do we find cholesterol? 14 Copyright © 1999, 2009 PJ Barnes & Associates x CONTENTS Where does the human body obtain its cholesterol? 15 What is the importance of cholesterol? 15 How is cholesterol delivered to where it is needed? 16 The effects of overabundance of cholesterol in blood 16 Can we have too much cholesterol in the diet? 17 Saturated fatty acids and hypercholesterolaemia: are all saturated fatty acids equal? ........................................................ 18 The importance of chain length 18 Influence of triacylglycerol structure 19 Mechanisms 19 Trans fatty acids: their influence on blood lipids and their wider health implications ........................................................... 22 Trans acids in the public eye 22 Trans fatty acids occur in nature 22 Isomerization produced by industrial processing 23 How much trans fat do we consume? 23 Metabolism of trans fatty acids 24 How might trans fatty acids be harmful? 24 Interactions with essential fatty acids Effects on biological membranes Influence on plasma cholesterol Conclusion 28 Cis-Monounsaturated fatty acids: are they really ‘neutral’? ...... 28 Background 28 The rekindling of interest in monounsaturates 28 Technical developments in monounsaturated oils 28 What do we mean by monounsaturates? 29 Influence on blood lipids 29 Practical implications 35 Dietary fat, blood lipids and health. Which is more important: total amount of fat eaten or its composition? ............................. 35 Content or composition? 36 Copyright © 1999, 2009 PJ Barnes & Associates