Tropical Nutrition and Dietetics

Abstract

India, together with Ceylon, have contributed so largely to the study of nutrition in tropical regions that it is a pleasure to welcome the second edition of this book. Dr. Lucius Nicholls is the Director of Nutrition in Ceylon and the author of several papers on malnutrition. The second edition has been considerably enlarged: there have been added tables of analysis of foodstuffs, diets have been suggested for institutions, and there are notes on food poisoning and insect pests. On the whole the book is a clear presentation of the facts of nutrition as they affect the inhabitants of the tropics, especially those who live in Asia. Those who live in Africa and the tropical parts of America, the Pacific islands and the East Indies are rather passed over; but this indeed is just, for far less work in nutrition has been done in these areas and it is only on published data that any author can draw. The study of nutrition and dietetics has advanced considerably further in the temperate regions of America, Europe, Australia and South Africa than has the study of the same subjects in tropical regions, and it has become a matter of great difficulty, and indeed uncertainty, to know how far the results obtained in the temperate regions can be applied to the tropics. Taken as a whole, those who have studied dietetics in the tropics consider that the inhabitants of these regions do not require as many calories or as much protein, mineral salts (except sodium chloride) or vitamins as are required in temperate regions. Some are positively parsimonious in the amounts which, they suggest, are required in warmer climates and by other races; at the other extreme another group follows with too little discrimination the results established in temperate regions. Nicholls adopts a position mid-way between the two and if the reviewer disagrees from certain of the conclusions of the book he wishes to make it clear that Nicholls has behind him a large weight of medical opinion in the tropics. At present the field of nutrition in temperate regions is dominated by what might be called the " optimal " school of thought. To explain what is meant by this, vitamin C [ascorbic acid] may be taken as an example. It is common knowledge that the clinical disease, called scurvy, is produced only when for many months a person has taken very low amounts of ascorbic acid. After the recognition of this fact the tests for sub-clinical scurvy were refined and it has been recognized that, although there may be no scorbutic haemorrhages, the intake of ascorbic acid may be inadequate to ensure the speedy healing of wounds, and that other morbid conditions may arise. It is unfortunately true that it is quite impossible to say where this state of sub-clinical scurvy fades into normal healthy nutrition, and laboratory tests for saturation with vitamin C [ascorbic acid] are probably artificial and yield fallacious results. Nevertheless, in view of all the known facts, nutritionists in temperate regions have agreed to advise an intake of ascorbic acid sufficiently high to guard against any reasonable fear of a deficiency. With our present spectacles we cannot detect the first signs of wear and tear: that is the case for the " optimal " school of thought. The position of the present reviewer is that we should only lower these standards, fairly reasonably established in temperate regions, to suit the inhabitants of the tropics when original observations, confirmed by several workers, suggest that there are certain racial or climatic variations peculiar to the warmer regions of the earth. It may well emerge that certain food constituents are needed in increased amounts in the tropics, sodium chloride is a case in point, others may be needed in decreased amounts, as calories to supply heat loss, but these estimates must be based on original work conducted in the tropics. If there is not enough food in the tropics to give its inhabitants the diet they require, and there is certainly not enough at the present time, we may bow to necessity but we will never lower our conception of the truth. Of all the food constituents required by man there is more certain knowledge concerning calorie requirements than anything else. Indeed in the question of calories we need not take the approach of the " optimal " school of thought; too few calories will mean either loss of weight or inability to do hard work; too many calories, adequately absorbed, will mean an increase of weight. Hunger and a sense of repletion maintain most of us in a delicately adjusted state of weight equilibrium. Let us see how the author approaches this problem. The discussion of calorie requirements commences on pages 164-172, where it is broken up into two or three portions, with paragraphs about protein and fat requirements in the middle. Under basal metabolism on page 165 there is no clear statement that B.M.R. depends on surface area; none of the recognized formulae, such as that of Du Bois, is given, so that B.M.R. cannot be calculated from a knowledge of the surface area which any given weight and height will produce. Nicholls states that a reduction of 10 per cent, in the B.M.R. can be allowed for the inhabitants in the tropics, and indeed some reduction is fairly generally accepted, but no reference is made to original observations on this crucial point. There is no clear reference to the Specific Dynamic Action (S.D.A.) of foodstuffs, usually taken as about 200 calories in temperate regions, which must be added to B.M.R. before the base-line to maintain body weight at rest can be drawn. On page 166 Lusk's estimate of the B.M.R. (no reference attached) is given as 1, 680 calories for a 70 kgm. man in temperate regions. Incidentally if the height of this 70 kgm. man is 5 foot 11 inches, then according to the Du Bois formula, B.M.R. (not including S.D.A.) would be about 1, 800 calories. The former figure of 1, 680 calories is regarded by the author as too high, and is reduced to 1, 500, as most of the smaller races of the tropics are not 70 kgm. in weight. Then follow the suggestions of the League of Nations Report (1936) advocating 2, 400 calories for a man or woman living an ordinary life in a temperate climate, but not engaged in manual work. This figure of 2, 400 calories is reduced by the author to 2, 100 calories (page 172), that is a reduction of 300 calories, although the suggested reduction in B.M.R. for the inhabitants of the tropics (page 166) was only 180 calories. To this figure of 2, 100 calories, to cover ordinary everyday living, the author adds 400-500 calories for the work of an " average labourer in the tropics." No comment was offered on the League of Nations Report (1936), given on page 166, concerning the calorie requirements for work, so that unless the mechanical efficiency of the labourer in the tropics is better than that found in temperate regions (usually in the region of 20 per cent., like that of a petrol engine), then these 400-500 calories for work are adequate for 6 hours of light work, or 4 hours of moderate work, or 2 hours of hard work, or 11/2 hours of very hard work. Some of us would like to add that in our experience the labourer, too often in the tropics, only does this amount of work, and we have suspected that one of the main reasons is that he does not get enough to eat. Protein requirements are far more generously dealt with in this book. An allowance of 65 gm. is quoted on page 173, on the advice of a single authority, , and appears to be the final conclusion of'the author. This conclusion is given as a small sub-section of a discussion on the calorie requirements. Previously the author gives, without comment, on page 166, the League of Nations (1936) recommendation of 1 gm. of protein for 1 kgm. of body weight in the adult. If the average weight of the labourer of Southern Asia is 52 kgm. (page 172),. then, in the opinion of the reviewer, 52 gm. of protein would appear adequate. As a matter of fact most of the discussion on protein requirements is given in chapter I, pages 9-23, and it is difficult to understand from this section whether the author feels that the figure of 18.75 gm. of protein (page 14) is grossly inadequate or needs considerable addition. No final opinion is given in chapter I, but one is referred at its end to dietary protein allowances in chapter IX. On referring to this chapter, on page 156, one finds it misprinted chapter XI,. but in any case it refers only to condiments and beverages. The reference at the end of chapter I probably refers to chapter XI, pages 167 and 173, but in any case one feels that the question of protein requirements has not been handled as a coherent whole. The reviewer does not wish to stress the viewpoint of the " optimal " school any further, especially in the less certain field of mineral and vitamin requirements. These are dealt with and their uses discussed in chapters II-VIII. The discussion is good and the facts are carefully recorded. Mention is made of the increased needs for common salt in the tropics; in subsequent editions it will be possible to discuss the deficiency that arises in heat-exhaustion. The parts concerning calcium are good: the author is of the opinion that an' adult in the tropics may require 0.5-0.7 gm. and a child 0.5 gm. The latter is about half the amount usually suggested in temperate regions. The anaemias found in the tropics are described on page 40 under iron requirements. Their classification on this page according to the colour index and cell diameter is based on a false premise, namely, that the colour index should always be exactly 1.0 and the corpuscular diameter should be exactly 7.2mu. Iron-deficiency anaemia and the liver-principle-deficiency anaemias are classified, and, as Nicholls suggests, these anaemias are frequently combined. The reviewer has suggested that this combination might be called " dimorphic anaemia "; the name, however, is not important, provided the