Human Nutrition: Current Issues and Controversies PDF
Preview Human Nutrition: Current Issues and Controversies
Human Nutrition Human Nutrition Cu rrent Issues and Controversies EDITED BY A. Neuberger T. H. Jukes Lister I nstitute of Preventive Department of Biophysics Medicine and Charing Cross and Medical Physics Hospital Medical School, London Department of Nutritiona~Sciences University of California, Berkeley M~iLIMnw International Medical Publishers Published in UK by MTP Press Limited Falcon House Lancaster, England Copyright © 1982 MTP Press Limited Softcover reprint of the hardcover 1st edition 1982 First published 1982 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical. photocopying, recording or otherwise, without prior permission from the publishers. British Library Cataloguing in Publication Data Human nutrition: current issues and controversies. 1. Nutrition I. Neuberger, Albert II. Jukes, T. H. 613.2 TX353 ISBN-13: 978-94-011-6260-9 e-ISBN-13: 978-94-011-6258-6 001: 10.1007/978-94-011-6258-6 Contents List of contributors vii Preface ix 1 Energy requirements in human beings 1 J. Garrow and S. Blaza 2 Fluoride and fluoridation of water 23 G. N. Jenkins 3 Nutritional status of North Americans 73 G. M. Owen and A. L. Owen 4 Nitrate, nitrite and N-nitroso compounds: biochemistry, metabolism, toxicity and carcino- genicity 87 L. C. Green, D. Ralt and S. R. Tannenbaum 5 Vitamin 0 141 H. F. Deluca 6 Vitamin A deficiency and blindness in children 185 S. G. Srikantia 7 Protein energy malnutrition (PEM) in children 197 S. G. Srikantia 8 Endemic pellagra 209 S. G. Srikantia 9 Nutritional eccentricities 217 J. H.Young 10 Laetrile, the bogus 'vitamin B 233 17' T. H. Jukes Index 243 v List of Contributors S BLAZA A NEUBERGER Animal Studies Centre The Lister Institute of Preventive Pedigree Petfoods Medicine Freeby Lane, Walton-on-the-Wold Charing Cross Hospital Medical Melton Mobray School Leicestershire LE14 4RT The Reynolds' Building England St Dunstan's Road London W6 8P, England H F DELUCA G MOWEN Department of Biochemistry Bristol-Myers Company, International University of Wisconsin-Madison Division 420 Henry Mall 345 Park Avenue Madison, WI 53706, USA New York, NY 10154, USA AL OWEN Owen Associates Inc. G S GARROW 251 Hilton Road Clinical Research Centre Westport, CT 06880, USA Division of Clinical Investigation Watford Road D RALT Harrow, Middlesex HA1 3UJ, Department of Nutrition and Food England Science Massachusetts Institute of Technology L GREEN 77 Massachusetts Avenue Department of Nutrition and Food Cambridge, MA 02139, USA Science Massachusetts Institute of S R TANNENBAUM Technology Department of Nutrition and Food 77 Massachusetts Avenue Science Cambridge, MA 02139, USA Massachusetts Institute of Technology 77 Massachusetts Avenue N JENKINS Cambridge, MA 02139, USA Department of Oral Physiology The Dental School S G SRIKANTIA University of Newcastle-upon-Tyne Postgraduate Department of Food Newcastle-upon-Tyne NE1 8ST, and Nutrition England University of Mysore Manasaga ngotri Mysore 570012, India T H JUKES University of California J H YOUNG Berkeley Department of History RSSF, 1414 Harbour Way So. Emory University Richmond, CA 94804, USA Atlanta, GA 30322, USA vii Preface This new volume deals with a number of important and current topics in human nutrition that we hope will be of general interest to those concerned with this subject. We have first of all a chapter by J. S. Garrow and S. Blaza on energy requirements, which has a direct bearing on the problem of obesity, and which largely affects the populations of developed and afiluent countries. This is followed by a chapter on fluoride and the fluoridation of water, under the authorship of G. N. Jenkins. The addition of fluoride to drinking water has given rise to a great deal ofd iscussion both amongst scientists and the public at large, and the present account tries to give the scientific background and a critical evaluation of established facts. The chapter by G. Owen on the nutritional status of North Americans is also likely to be of interest to other countries, as the techniques used and the problems encountered are similar to' those encountered in other parts ofthe world. A chapter on nitrates, nitrites and nitrosamines by S. R. Tannenbaum discusses a topic which again has engendered widespread interest amongst a large number of people, and where a balanced presentation of the relevant facts is particularly important. One of the fields in which biochemistry, physiology and nutrition have made enormous advances over the last few years is that of vitamin D and the new knowledge acquired on control of the metabolism of calcium and phosphorus. This information is critically discussed by H. DeLuca. The developing world, which comprises the majority of mankind, has always had its special nutritional problems, and these vary from country to country. The problems chosen by S. G. Srikantia appear to be of special importance, and these are vitamin A deficiency, protein energy malnutrition, and pellagra. Whilst more knowledge is still required on many of these topics, the chief difficulty is in applying existing knowledge to the complex social, economic and political realities of the various countries concerned. We have a chapter by J. Harvey Young who deals with nutritional eccentricities, also choosing entirely American examples. This account emphasizes the different problems facing scientists and others who are concerned with putting sound nutritional advice to the population at large. These difficulties emphasize the fact that human beings are not entirely rational and irrational considerations play a large part in attitudes adopted by individuals and groups to many problems, but particularly with respect to the diet people wish (or are persuaded) to consume. In the last contribution one of us (T. H.Jukes )discusses ix HUMAN NUTRITION the widespread use oflaetrile, a substance which has received much publicity, especially in the USA. Several important topics in nutrition have not been covered, but we have tried to deal with the fields which are of particular importance at the present time. Thomas H. Jukes Albert Neuberger x 1 Energy requi rements inhuman bei ngs J. GARROW AND S. BLAZA INTRODUCTION A dietary source of energy must occupy a central place in any nutrition scheme, since energy requirements must be met even at the expense of protein requirements. However, dietary energy requirements are difficult to define in anyspecies;al1d particularly so in human beings. The nutritional objective of livestock farmers -is clear: tliey llave fo rruse their animals as profitably as possible. For a given strain of pig, for example, a certain ration can be shown to be optimum to yield the most meat at least cost, but such criteria do not apply in human nutrition. The human nutritionist cannot play safe and recommend aminimumofene!,gyin the diet. Itis possibletodefine'enough;yjtamin C, and if tKe requirement is exceeded not much harm is done, but the same lati{ude does not apply to energy intake." Grossly excessive and" grossly deficient energy intakes are both damaging to health. At least in the short term, there is no need for energy intake to match expenditure, since a temporary excess or deficit can be met by adjustment of the energy stores of the body, chiefly in the form of fat. In the long term, of course, intake must match output, but alterations in the energy stores of the body are themselves associated with alterations in metabolic rate, and hence in energy requirements. Therefore, to discuss energy requirements it is necessary to consider in turn energy expenditure, energy stores, and then the adaptive responses which tend to stabilize energy balance. Energy units Until the change to SI (Systeme Internationale) units, human energy intake and expenditure was usually expressed as kilogramme calories (kcal). The SI unit is the joule (J), and the conversion: 1 kcal = 4.18 kJ Since direct calorimeters are usually calibrated with respect to electrical standards, the rate of heat output by direct calorimetry is expressed as watts: 1 watt = 1JI s, so 1 kcaljmin = 70 watts. HUMAN NUTRITION When energy expenditure is measured by indirect calorimetry, the heat equivalent of the respiratory exchange can be calculated using the Weir formula 1• However, a fundamental limitation of the accuracy of indirect calorimetry is that the mixture of expired gases does not necessarily reflect the metabolic mixture being produced in the tissues. CO may be stored in the 2 tissues, so the apparent RQ may not equal the metabolic RQ. For this reason it is prudent to report the results obtained in indirect calorimetry in terms of oxygen uptake, rather than converting to heat production using an assumed value for the heat equivalent of oxygen which may not be correct. However, to provide the reader with an easy conversion of oxygen uptake to energy expenditure the following equation will suffice: Oxygen uptake (mljmin) x 7 = kcal/day. ENERGY EXPENDITURE Techniques for measurement of energy expenditure (a) Direct calorimetry The classical studies on human energy expenditure were performed by Atwater and Benedice with a direct calorimeter. This was a copper box 2.15 m long, 1.22 m wide, and 1.93 m high. The subject entered through an aperture 49 em wide and 79 em high; the aperture was then sealed with a sheet of plate glass embedded in molten beeswax. Great care was taken to ensure that there was no heat gradient across the walls of the calorimeter, and the heat produced but the imprisoned subject was exactly removed by careful regulation of the flow of cold water through pipes inside the chamber. In the ensuing 70 years there have been considerable advances3•4•s making calorimetry less arduous for both the subject and the investigators, but the accuracy of the original apparatus has not been surpassed. The great advantage of direct calorimetry is its accuracy and ease of calibration. An electrical heat source, or a lamp burning ethyl alcohol or butane, can be used as a reference standard, and the observed heat production should agree with the theoretical value within 1 %6. The qisadvantages of direct calorimetry are that it is expensive, laborious and slow. The design of a relatively simple direct calorimeter?, which was constructed by the Division of Bioengineering at the Clinical Research Centre in 1976, is shown in Figure 1. The calorimeter chamber (2m wide by 1.7m deep by 2m high) is constructed of slabs of expanded polystyrene (P) 20em thick, faced on the inner and outer surfaces with sheet aluminium. Access to the chamber is by a door in which there is a pass-through hatch (H), with clear plastic panels hinged in the inner and outer faces; this also provides a window. The chamber is furnished with a bed, chair, table, small television set and radio-tape recorder. The great majority of patients admitted to our metabolic unit are quite willing to spend a period of 26 hours in this chamber on several occasions. The air inside the chamber (volume approximately 6m3) is circulated by an axial fan (F) along a duct into a plenum chamber lOem deep covering the 2 ENERGY REQUIREMENTS Figure 1 Diagram of the direct calorimeter at the Clinical Research Centre, Harrow. For description see text whole area of the right-hand wall of the chamber. The inner wall of this chamber is made from perforated hardboard, so the air escapes into the chamber and flows in a laminar fashion from right to left across the chamber and enters a similar plenum chamber on the left-hand wall. From here it is sucked down to the duct, where part of the stream of air passes through a heat exchanger (X), and part bypasses the heat exchanger. The proportion of the circulating air which is cooled in the heat exchanger is determined by the position of the shutter (S), which is driven by a servo motor which is sensitive to the temperature gradient across the walls of the chamber. Thus, if the thermistors mounted on the inner and outer aluminium skins of the chamber detect a new outward flow of heat across the walls, the servo motor is instructed to move the shutter so a larger proportion of the circulating air is cooled, and if the net movement of heat through the walls is inward the shutter moves in the opposite direction to reduce the amount of heat extracted from the circulating air. In this way the heat flow across the walls is kept close to zero over any long period, so any heat produced by the subject in the calorimeter is quantitatively extracted in the heat exchanger. Heat loss by convection and evaporation is not separately measured, since evaporative heat 3
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