Omega-3 fatty acids and health

371 Pages·1995·49.39 MB·English

by  Joyce A. Nettleton D.Sc

OMEGA-3
FATTY ACIDS
HEALTH
AND
OMEGA-3
FAIIY ACIDS
HEALTH
AND
Joyce A. Nettleton, D.Sc, R.D.
Institute of Food Technologists
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V
A Thomson Publishing Company
ArI direction: Andrea Meyer, emDASH inc.
Cover design: Saeed Sayrafiezadeh, emDASH inc.
Copyright © 1995
Springer Science+Business Media Dordrecht
OriginalIy published by Chapman & HalI in 1995
Softcover reprint ofthe hardcover Ist edition 1995
Ali rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any
form or by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or
information storage and retrieval systems-without the written permission of the publisher.
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Library of Congress Cataloging-in-Publication Data
Nettleton, Joyce A., 1944-
Omega-3 fatty acids and health / Joyce A. Nettleton.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4613-5860-2 ISBN 978-1-4615-2071-9 (eBook)
DOI 10.1007/978-1-4615-2071-9
1. Omega-3 fatty acids-Physiological effect. 2. Omega-3 fatty acids-Health aspects. 1. Title.
QP752.044N48 1994
612.3'97-<ic20 94-20759
CIP
British Library Cataloguing in Publication Data available
for Coby
Contents
Foreward ix
Preface Xl
Acknowledgments Xlll
Introduction to Fatty Acids 1
Types and sources offatty acids 1
Fatty acids in fish and shellfish 17
Omega-3 fatty acids 28
References 45
2 Omega-3 Fatty Acids and Health 64
Early history ofOmega-3 fatty acids 64
Epidemiological evidence for the healtheffects ofOmega-3 fatty acids 67
References 74
3 Omega-3 Fatty Acids and Heart Disease 77
Current understanding ofheart disease 77
Effect ofOmega-3 fatty acids on plasma lipids 85
Effects ofOmega-3 fatty acids on cardiac composition and function 93
EffectsofOmega-3 fatty acids on lipoproteins 98
References 116
4 Omega-3 Fatty Acids and the Vascular System 138
Hemostasis 138
Platelet function 146
Blood pressure 154
Stroke 163
References 167
viii I Contents
5 Omega-3 FattyAcidsand Immune!lnflammatory Responses 187
Eicosanoids 187
Leukotrienes 194
Leukotrienes, inflammation and immunity 200
Leukotrienes indisease 204
References 223
6 Omega-3 Fatty Acids inEarlyHumanDevelopment 249
Omega-3 fatty acids in neural development 249
SourcesofOmega-3 fatty acids for infantdevelopment 265
References 275
7 Omega-3 Fatty Acids in OtherDiseases 287
Diabetes 287
Multiple sclerosis 298
Cancer 308
MiscellaneouseffectsofOmega-3 fatty acids 324
References 328
Index 355
Foreword
Theevidence that omega-3 fatty acids areessential for human developmentand
most helpful to achieve good health throughout life is clearly documented by
Dr. Joyce Nettleton in her new book Omega-3 FattyAcidsandHealth. Omega
3 fatty acids are produced by the plants ofthe land and sea. The tissues ofthe
body require the omega-3 fatty acids for their proper functioning just as they
also need the omega-6essential fatty acids. Itis probable in man'sevolutionary
development that there has always been the proper balance between these two
groups of essential fatty acids, but in the modern era with the provision of
inexpensive vegetable oils it is possible that the pendulum for increased dietary
omega-6fatty acids in theform oflinoleic acid has swungtoo far and the intake
ofomega-3 fatty acids hasactualIydeclined. Inparticular, the22carbonomega
3fatty acid, docosahexaenoic acid, which has six double bonds, is important in
themembranesofbraincells, heartmusclecells, the rodsandconesoftheretina
and spermatozoa. Docosahexaenoic acid is found only in foods such as fish and
other sea life, having been synthesized by the phytoplankton ofthe waters.
An outright deficiency ofomega-3 fatty acids has led to a number ofdistur
bances in animals and human infants such as impaired vision, abnormalities of
the electroretinogram, of the eye and various behavioral aberrations. The old
adages that fish is "brain food" and "a mackerel a day keeps the doctor away"
areingrainedinourcultureandthecurrentscientificevidenceindicatethevalidity
of folk wisdom. Before the development of infant formulas as we now know
them, all babies were given a teaspoon ofcod liver oil per day which supplied
not only vitamins A and Dbut quantities ofomega-3 fatty acids, especially the
most important one, docosahexaenoic acid. Many adults also continued this
practicethroughout theirlives. This rich sourceofomega-3 fatty acids has been
discarded in recent years. Infant formulas do not contain docosahexaenoic acid
buthuman milkdoes. Thereisaconsiderabledriveonthepartofsomescientists
to induce infant formula manufacturers to include docosahexaenoic acid as well
ix
x / Foreword
as other fatty acids that are present in human milk but which are not yet vital
components ofcommercially available infant formulas in this country.
The other side ofthe coin about the importance ofomega-3 fatty acids from
fish is their likely prevention of many chronic diseases now rampant in our
country. These especially include coronary heart disease and even some forms
of cancer. The omega-3 fatty acids from fish and fish oil tend to block the
development of atherosclerosis. The consumption of fish prolongs survival of
thoseafflictedwithcoronaryheartdiseaseandreducesthenumberofsubsequent
heart attacks. These omega-3 fatty acids interfere with abnormal clotting ofthe
blood which leads to coronary thrombosis. They may be active also against
certain immunological diseases, hypertension and hyperlipidemic conditions.
Populations that include fish and other sources ofomega-3 fatty acids from the
oceans, lakes and rivers generally seem healthier. These include the Japanese,
the Dutch and the Greenland Eskimos who had less coronary disease despite a
highfat, highcholesteroldiet. Theyareprotectedbyahighintakeoftheomega
3 fatty acids from seal, whale and fish.
Omega-3FattyAcidsandHealthclearlydistinguishesbetweentheomega-3fatty
acidssynthesizedbytheplantsoftheland(linolenicacid)andtheeicosapentaenoic
anddocosahexaenoicacidssynthesizedbytheplantsofthesea,thephytoplankton.
Onlybytheconsumptionoffishandotherseafoodwillthedietcontaineicosapentae
noicanddocosahexaenoicacidswhichare20and22carbonsinlength. Vegetable
oils,cereals,allvegetablesandfruitswillcontainonlythe18carbonlinolenicacid.
Whilethebodycansynthesizethelongerchainomega-3fattyacidsfromlinolenic
acid,thissynthesismayberatelimitedand, inparticular,thesynthesisofdocosa
hexaenoicacidfrom linolenicacidappears veryslow. Thesedistinctions may be
importantintwoareas:infantformulasandinthepreventionofadultdisease. Lin
olenic acid iscurrentlypresent in infantformulas butnotdocosahexaenoic acid.
Humanmilkcontainsboththeseomega-3fatty acids: linolenicanddocosahexae
noic acids. There is littleevidence that the consumptionofvegetableoilsrich in
linolenic acid will have thesamebeneficial effectin preventingortreating these
chronicdiseasessuchascoronaryheartdisease.
Joyce Nettleton has provided a most valuable very up to date contribution for
those seeking to understand the role offatty acids in health and disease and, in
particular, the omega-3 fatty acids. Since Omega-3 Fatty Acids and Health is
both practical and theoretical, it will appeal to all health professionals, to food
scientists, and to the well informed non-professional reader.
William E. Connor, M.D.
Professor ofMedicine and Clinical Nutrition
Oregon Health Sciences University
Portland, Oregon
Co-authorofThe New American Diet
FormermemberoftheFoodandNutritionBoard,NationalAcademyofSciences
Preface
Now that we are aware ofthe immense scope ofomega-3 fatty acid activity, it
seemsincrediblethatthese substanceswereoverlookeduntil nearlytwenty years
ago. Discovered decades ago, omega-3 fatty acids in fish oils were obscured in
partbytheabilityofvegetablepolyunsaturatedfatty acidstolowerbloodcholes
terollevelsandhencepotentiallyreducethe riskofheartdisease. Ironically, fish
oils,themajorsourceofomega-3fattyacids,appeartohaveevengreaterpotential
than vegetable oils for deterring coronary disease.
Omega-3 Fatty Acids and Health describes the remarkable developments in
fish oil research in the past fifteen years that have turned traditional thinking
about fatty acids upside down. Starting with the striking observation that the
native Inuit high fat diet is associated with the absence ofheart disease, to the
careful studies demonstrating the involvement ofomega-3 fatty acids in human
growthanddevelopment,Omega-3FattyAcidsandHealth leadstothethreshold
of understanding how these fatty acids function in the immune system and in
cancer. Scrupulouslydocumented, the bookrelatestheunfoldingofnew knowl
edge that has broadened our understanding of fatty acid function in health and
disease.
The involvement of omega-3 fatty acids in heart disease, where these sub
stances have been most extensively studied, is discussed in detail. Probing how
omega-3s function in the prevention ofheart disease has forced a reassessment
of the development of this widespread condition. Modem ideas have shifted
from fixation on cholesterol in coronary arteries to the complex interactions
involving the heart muscle itself, blood vessels and cells, lipid metabolism and
immune function. We now think of heart disease not just in terms of lipid
metabolism but also the regulation of hemostasis, the electrical and chemical
activities of the heart, cell to cell interactions, and responses of the immune
system. Because omega-3 fatty acid activity crosses the boundaries of these
systems, it has changed, almost singlehandedly, ourunderstanding ofthis com-
xi
xii I Preface
monailment. Itwillnotbesurprising,therefore,thatmanyobservationsdescribed
in Omega-3 Fatty Acids andHealth have direct implications for better health.
Equallyfascinatingfromanentirelydifferentperspectiveistherecentdiscovery
of the importance of omega-3 fatty acids in human development. Selectively
concentratedduringfetaldevelopment, omega-3fatty acids, particularlydocosa
hexaenoic acid, are incorporated into neural tissues, notably brain and retina.
Their function in these tissues is only now being unravelled. This research has
already led to changes in the composition of infant formulae and holds clear
implications for maternal and infant nutrition as well.
Thebookprovidesbackgroundandrefresherinformationaboutfattyacidsand
their contribution to health and disease for readers not working in the field of
lipid metabolism. Itdetails theemergenceofomega-3fatty acids, first as appar
entlynovelsubstances,thenasessentialnutrientsforhumangrowthanddevelop
ment. The book moves from the historical development ofomega-3 fatty acid
research, through recent media publicity about fish oil supplements, to current
issuesfacing today'sscientists. In addition toreviewingresearchdevelopments,
Omega-3FattyAcidsandHealthexplainsthe findings andweighs theevidence.
The bookstopsshortofhighly technicaldetailed interpretationsofexperimental
findings or speculative molecular mechanisms ofaction.
The work draws entirely on the peer-revieWed scientific literature. Findings
includeepidemiological, biochemical and clinical studies, someofwhichare in
the early stages ofdevelopment. Advancemeqt has come at an astonishing pace
for scientific study, yet firm conclusions remain elusive and maddeningly com
plex. Thus, the findings described here are not intended to be prescriptive,
especially for readers with health conditions; ailments are best treated by a
physician. Readers may, however, develop a certain fondness for fish.