Abstract:
Proc. Aust. Soc. Anim. Prod. (1974) 10; 181 HUMAN NEEDS FOR.MEAT MJ. TRACEY There are nine or ten amino acids used in the synthesis of human proteins which most men, probably all men, cannot synthesize or cannot synthesize in adequate quantities. They are accordingly known as the 'essential' amino acids. Since man's enteric fauna and flora are a negligible source of the nutrients he absorbs, his diet must contain proteins which will after proteolysis supply his needs for the essential amino acids he appears unable to produce for himself. No life appears possible on our planet without protein, as was pointed out by Miider in 1845, and this appears to be a necessary consequence of protein's unique role in the cellular machinery-- a role that apparently requires the presence of all the essential amino acids in the proteins playing it. Protein is also used in the structure of cells and in the extracellular structures of the body. The requirement for variety in amino acid composition appears much less in this instance, which is why between a third and a half of the protein in a domesticated food animal is less than adequate from the point of view of man's nutrition. A consequence of the essential unity of life is that the composition in terms of amino acids of the cellular machinery of man, a green plant, or a bacterium is 'essentially similar, while structured proteins such as collagen, protective proteins such as keratin, and storage proteins such as gluten may, and in fact do, have compo@tions which depart from the norm in that they frequently completely lack some amino acids or ' may contain quite unusual component amino acids such as hydroxylysine. Meat, therefore, could only be an essential component of man's food if it contained an essential amino acid not occurring in the plant kingdom, or some other essential dietary factor not occurring in the plant world. Meat does contain peculiar amino acids not yet found in the plant kingdom, methylhistidine and s methyl lysine, but these, unfortunately perhaps for the meat producer, are not required as such by man for incorporation into his own muscle protein - he puts in histidine or lysine first and methylates them afterwards. Meat and other animal tissues do, however, contain one substance not found in a green plant and essential for man's life cyanocobalamin or vitamin B12. Man's minimum requirement for B12 is very small - about a tenth of a microgram per day, though ten to twenty times this amount is regarded as desirable. The minimum amount could be supplied by 5 g of beef a day or 100 mg of liver or 30 ml of milk a day. The vitamin is not found in green plants, and it is something of a mystery how strict vegetarians survive a diet containing no animal products and there/fore no B12. However, the amount required is so small that it is difficult to exclude the possibility of some 'contaminationT of the vegetable foods by either animals (as all who have eaten cauliflower will know) or microorganisms. Ten grams of good fertile soil contains enough lower forms of life, both animal and microbial, to supply a day's minimal requirements of B12, and so, under some circumstances, do five litres of freshly fallen rain. Nevertheless, in spite of the very small quantities of B12 that are needed, a rigorous vegetarian who eats no animal products at all (a vegan) may succeed in inducing a B12 deficiency in himself. The first reported cases in Australia were identified in Perth in 1963. Both patients were in their seventies, one had been a vegetarian for 30 years and a vegan for 18 years, the other had been a vegetarian for 15 years and essentially a vegan for only one CSIRO Division of Food Research, P.O. Box 52, North Ryde, N.S.W.9 Australia. 181 year (Connor and Pirola 1963). Both improved dramatically whenB12 injections were given, the recovery of the vegan of 18 years' duration being speeded up by her acceptance of all milk, eggs, and butter available in the ward diet from her admission onwards. Since adequate &mounts of vitamin B12 can be got by drinking less than half a pint of milk a day as the sole source of animal protein, there is no demonstrable nutritional necessity for the consumption of meat, and if need is equated with necessity, there is strictly no need for meat, and I should have no more to say. Necessities are qualified, however, as absolute, conditional, logical, moral, natural, philosophical, theological, and physical, and using these useful categories for human needs we can, having disposed of the absolute need as being non-existent, proceed to discuss at least the conditional and the moral categories. The conditional we have already covered, but it may be made explicit by stating that man does not need meat unless he consumes no other animal food (including the invertebrates - a dozen oysters contain a year's supply of B12) and no prokaryotic organisms. If this condition is met, then he needs meat - or vitamin B12 concentrate from a bottle. The moral category includes 'that kind of probable evidence which rests on a knowledge of the general tendencies of human nature or of the character of particular individuals or classes of men'. The moral necessities or needs of man may perhaps be conveniently distinguished as' 'wants', and are much more likely to be significant at the market or economic level than are his absolute necessities as long as these are unrecognized except .by a vanishingly small proportion of the population. What would help in considering this category is some knowledge of the feelings and desires in relation to meat that are experienced by men unconfused by the facts of nutrition or by what may be currently believed to be facts of nutrition. Those totally ignorant of nutrition and unexposed to nutritional views put forward by advertisers , peddlers of vitamin pills, and digest writers, are unfortunately likely to be restricted to deaf analphabetics, which is not very helpful. We can, however , perhaps rely in some degree on a sample of literate intelligent writers who have voiced their views on nutrition in almost total ignorance of any of what we now regard as the basic facts of biochemistry and physiology. These are those who wrote on human nutrition more than a century ago. They voice opinions which seem to me to give a coherent version of much that lies unformulated in the minds of most of today's populations beneath any subsequent accretion of information, erroneous or otherwise, that has arisen from recent advances in science. Let me give an example from Dr William Nisbet, whose 'Practical Treatise on Diet and on the most salutary'and agreeable means of supporting Life and Health by Aliment and Regimen adapted to various Circumstances of Age, Constitution, and Climate and including the Application of Modern Chemistry to the Culinary Preparation of Food* was published in London in 1801. He says 'After these introductory remarks on food in general, we shall now consider the first species of it, or m2imaZ food, more particularly. Animals of all kinds are eat by the inhabitants of different countries, not excepting even vermin apparently of the most disagreeable nature. This general desire for animal food can only proceed from an instinct for it; and in a cold climate the restrictions to its use should by no means take place in the degree that some authors have recommended.' 182 Mr James Johnston, Fellow of the Royal Societies of London arid Edinburgh, writing in 1055, has some further points of nutritional belief and observation that will be familiar to this audience. He says 'The flesh of wild animals is represented very nearly by the lean beef of which the composition is given above. Wild animals generally contain little fat. But it is not so with our domesticated animals, and especially such as are reared for food. They all contain much fat, either collected by itself in various parts of the body (the suet or tallow), or intermingled with the muscular fibre, as in the highly-prized marbled beef in which the English epicure delights. In the boiling-houses at Port Phillip, a small merino sheep of 55 lb. weight gives 20 lb. of tallow, which is nearly two-fifths of the whole. In heavier sheep the proportion of fat increases, four-fifths of all the weight above 55 lb. being tallow. In beef and mutton, such as is met with in our markets, from a third to a fourth of the whole dead weight generally consists of fat.* and further, 'It appears, therefore - ................... That the proportion of fat is variable, and that those varieties of animal food are most esteemed for human food in which a considerable proportion of fat is present. Hence, Where the proportion of fat is naturally small, we endeavour to ' increase it by art; as in feeding the capon. Or we eat along with th,ose varieties in which it is small some other food richer in fat. Thus, we eat bacon with veal, with liver, and with fowl; or we capon the latter, and thus increase its natural fat. We use melted butter with our white fish, or we fry them with fat; while the herring, the salmon, and the eel, are usually both dressed and eaten in their own oil. If the reader will take the trouble of consulting any popular cookery-book, he will find that sausage, and other rich mixed meats, are made in general with one part of fat and two of lean - the proportion in which they exist in a piece of good marbled beef! Art thus unconsciously again imitating nature.' We can say, therefore, that it is probably a 'natural' or 'constitutional' or 'inbuilt' desire of man to eat meat preferably accompanied by fat. Another and perhaps more convincing, and certainly more fashionable, line of evidence is to examine what happens when man is offered the economic opportunity of increasing the amount of meat in his diet. Animal protein consumption throughout the world varies very greatly in its levels, from the population of Iceland representing 0.000,055$ of the world population who eat a diet containing more than 75% of its protein as animal protein, to some tropical countries accounting for 2.75% of the population who achieve less than 10%. Populations eating more than 50% of their protein as animal protein include those of the whole of North America, 78% of Oceania, 53% of Europe, 11% of Latin America, while populations reaching this level in Africa and Asia include less than 1% of these continents' population. There is an obvious economic correlation between standard of living throughout the world and meat consumption (Figure 1). 183 If we now look at changes in individual standard of living, the picture is even that as agricultural production rose in production increased 4.4%, while that of TABLE 1 countries during times of rising clearer. Thus in Table 1 we see Taiwan from lg65-lg70, plant food livestock increased 45%. In Japan from 1949-1968, while total protein consumption per head rose l%, consumption of animal protein doubled, with, of course, a sharp decline in plant protein intake (Table 2). 184 TABLE 2 That the process is by no means complete even in advanced countries is shown by the results of a survey in France in 1968 (Table 3); 53% of the population TABLE 3 declared that they would like to increase their consumption of meat if possible, and even among the professional classes the proportion was still high at 32%. The human desire for meat that obviously exists cannot be met in the foreseeable future, and there is a real possibility that the increase of world population will outpace the increase in supplies of meat, thus exacerbating the demand as standards of living rise. The inadequacy of world production of animal foods does not mean necessarily that the demands of the consumer will not be met at least in part. Food is identified by the consumer in terms of texture, flavour, and appearance, and is valued by him in terms of past likes and dislikes. Thus, if he likes meat, a food looking like meat with the flavour and texture of meat will be accepted as meat, unless prejudice is aroused by its prior description as 'synthetic', 'substitute', or simply knowledge that it is not meat. Consequently it is possible to give the consumer a product not chaining meat at all, or containing little meat, and satisfy his demands for meat. Such meat-like products have, as you will know, been prepared on a commercial scale with very considerable success. Not all forms of meat can be successfully simulated, but a very wide range can be. The products are prepared by the processing of plant seed proteins to form two distinct ranges of a product. The more sophisticated and more expensive product has a visible fibrous texture closely resembling that of natural meat, while the less elaborate and cheaper product has the flavour and texture of meat in a granular form. In this state it is an excellent diluent for minced or finely divided meats, and in addition has the commercially valuable property of immobilizing more water and fat than meat protein. It is forecast that this material may account for lo-15& or even, in the views of some, 20% of the total domestic 'meat* consumption in the U.S.A. by 1980. Some early attempts to market meat analogues in Europe have not been 185 future, particularly at 'the bottom end of the market', as the early ance of Kesp as a meat pie filling in the United Kingdom in 1973 has Marks (1971), for example, has calculated that if it is assumed that thetic' meat has replaced 20% of the total manufacturing beef market there will still be a shortage of beef in the United Kingdom even if a success, but there is every likelihood that success will come in the near acceptshown. 'synby 1980, it is assumed that production increased by 2% per annum to l,OOO,OOO tons due to increased population and demand. The present EEC is 'only 86% self-sufficient in beef, and demand is increasing rapidly. In contemplating the effect of advances of food technology on meat consumption by making it possible to use plant-derived foods in place of animal foods, we must remember that it has happened before. One of the few new food products produced in the last century (as distinct from imitations of old foods, like margarine) was the breakfast cereal. This displaced progressively the animal foods of egg, bacon, and chops from the breakfast tables 186 of much of the Anglo-Saxon world. The impact of the new advances in processing of plant-based protein foods will, of course, not be so obvious, as it will not initially take the form of a new food form displacing an old one, but rather of a new product in conventional guise replacing a proportion of the consumption of an old, as margarine has with butter. Moreover, it must be remembered that its main impact on a world-wide basis is likely to be additive rather than substitutive. The history of the market conflict between margarine and butter in the advanced society of the United Kingdom is of some relevance. Before the first world war and 40 years after the appearance of margarine on the market, butter consumption was 16 lb per head, and margarine had 27% of the total spread market. In 1966, half a century later, butter consumption had increased to 20 lb per head although margarine now accounted for a larger share of the total market - 37%. The total consumption per head of butter and margarine had risen during half a century by 10 lb per head, and of this increase 40% was butter. The potential for an increase in the world consumption of protein is probably greater than that which was present in the United Kingdom for fat, and it is likely that meat consumption per head will increase steadily, particularly in the more rapidly advancing nations, although plant protein in meat extender and analogue form will increase, too, until it occupies a significant proportion of the total 'meat' market. One forecaster has suggested that in 2000 they may occupy 25% of the total (very much enlarged) market in the U.S.A. Other advances in food science and technology are onthe horizon, and while they will alter the details of the picture I have painted, they will not, I believe, affect its general nature. While meat extenders and analogues are at present made from plant seed proteins (soy and wheat), there are possibilities that they may be prepared from the 'single cell proteins' derived from yeasts, fungi, and bacteria grown with hydrocarbon or waste carbohydrate energy sources and inorganic nitrogen. I believe their impact for many years will be on the animal's food and not man%. It is likely that they will increasingly replace the seed proteins in animal foods and release increasing quantities of seed protein for use in human diets. It now appears possible to produce ruminant meats and meats of other animals in which the composition of the fat has been controlled in a desired direction. I believe these meats have a significant future, but they will do no more than replace meat of conventional composition in the diet, and are unlikely to have any significant impact on total demand for meats. The use of protected supplements on which their production is based may, however, have significant effects in increasing the efficiency of production of meat by increasing the yield of ruminant meat per unit of feed. REFERENCES ANON. (1973). London Times. BLAXTER, K.L. (1970). Proc.Nutr.Soc. 29: 244. BROWN, L.R. (1972). PAG Bull. 2(2): 25. CLAUDIAN, J., and SERVILLE, Y. rlg68). Cah.Nutr.Diet. 3(3): 29. CONNOR, P.M., and PIROLA, R.C. (1963). Med.J.AuSt. ii,-51. JOHNSTON, J.F.W. (1855). 'The Chemistry of Common Life' Vol.1. (Blackwood: Edinburgh). MARKS, H.F. (1971). In 'New Protein Foods: Report of a Conference'. (University of Reading. Agricultural Development Association). P.47. MULDER, G. J. (1845). 'The Chemistry of Vegetable and Animal Physiology'. (trans. by Dr Fromberg: Berwick). NISBET, W. (1801). 'Practical Treatise on Diet . . . . . . . . ...'. (London). OISO, T. (1971). Rep.natn.Inst.l!?utr,, Tokyo 1971: 46. 187