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This article was published in 1964
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
The World and its Future Food Supplies
M. V. TRACEY, M.A. Senior Principal Research Officer, C.S.I.R.O. Wheat Research Unit, North Ryde, N.S.W.
Though science fiction and current technological abilities have shown stimulating signs of convergence in recent years, we cannot, in the future, rely on Tennysonian argosies dropping from the blue with costly bales of extra-terrestial food supplies. Food for mankind's future must be grown on the earth, and this fact sets a limit to its population. It is a truism to say that food is a source of energy, its corollary is that the production of food requires energy. Man as a power source runs at about 130 watts and the food that must be burnt to maintain this output amounts to about a pound of dry matter a day. For our present population of 3,000,000,000 this amounts to 1.35 million metric tons a day or close to half a billion tons of dry matter a year. This is our current desirable expenditure, an expenditure we do not achieve, and the demand is steadily increasing. The energy source for the synthesis of this food is directly, or indirectly, the sun, the synthetic agency directly, or indirectly, the plant. The plant cover of the world uses approximately 0.1% of the total solar energy incident of earth. The world's income from photosynthesis is shown in Table 1, in which the net production of organic matter per year is listed in terms of carbon content. The gross production is larger, but is reduced to the net figure by respiration. The carbon content of man's food is about 60% by weight. So, in terms of carbon, the total potential food produced per annum is in the region of 150 billion tons. If, after harvesting. removal of inedible products such as lignin and cellulose (for physiologically we are neither termites nor cows), and allowing for waste, 10% of this total were available as completely digestible food for man, then his present population could increase thirty fold. But, of course, he would have to remove other herbivores from the earth's surface (after which carnivores would not last long), and take care to occupy no new land or sea surface already used for photosynthesis. He could live at the poles or beneath the surface of the sea. A feature of considerable interest in Table 1 is the relative inefficiency of cultivated crops in fixing carbon. The average production of the uncultivated areas of the earth is 486g carbon / square metre / year — some 4½ times greater than that for the cultivated areas — but, of course, the cultivated land gives a higher percentage yield of useable food and a negligible yield of newsprint and lumber.
If man revolts at the prospect of living as a complete vegetarian on a world in which he is the only visible animal species, he could, at a cost, eat nothing but meat. The cost is a 90% reduction in maximum population to 9 billion. This assumes that all food chains were reduced to three links, plant — herbivore — man, and would be difficult to achieve in the sea. Man would then be the sole carnivore. These then are two theoretical population limits arrived at from ruthlessly simplified assumptions, and both in practice impossible to achieve; an upper of 90 billion and a lower of 9 billion. If man wants to remain a land animal both must be reduced still further.
These theoretical limits are well above the present world population of 3 billion, and we must examine the reasons for the concern that is shown about the current increase in population. The figure shows the population history of man since he first lived on earth, though much of the detail can only be the result of informed guess work. In the upper graph it will be seen that there has been a very steady slow increase in population over the millennia with a recent explosive increase. The lower graph is plotted on a logarithmic scale and shows the three growth periods of man in his 1,000,000 years of existence. The beginnings of these periods have followed the invention of tools, the invention of agriculture and the application of science. At present the top curve ends at a figure of 3 billion and the figure will increase. Here and there in the world there are signs of a slowing down in the rate of increase, but the general outlook appears to be that the increase will continue on a world basis at an accelerating rate. An increase of 2% a year — the current figure for Africa — doubles population in less than 40 years. The figure for Africa threatens to reach 3%. In fact it must be obvious that, with 2/3 of the world's population already undernourished, we have already reached the limit as long as our habits, social organisation, and method of running the affairs of mankind persist. They cannot persist without calamity in the form of widespread death due to hunger, war or pestilence unless some changes are made. It is my task to discuss some of the changes that are beginning to be made in the field of nutrition and to suggest the lines along which further changes are inevitable. It is my limitation that changes in social structure, practice, and conscience, to say nothing of political organisation, essential though they may be, are outside the scope of this paper.
What then is being done now to palliate as far as possible the hunger of the majority of the world? The most widespread and important form of malnutrition today is that of protein deficiency which tends to be particularly severe in young children. It is a result, in some areas, of both social and physical causes — a result, that is, of children not being given available protein because it is thought that they do not need it, and a result of actual shortage of protein. A massive programme of nutritional education and supply of protein rich foods is being carried out by F.A.O. and UNICEF. An active search for sources of protein, which are often wasted, and are therefore cheap, has also gone on, and these protein sources have been evaluated in terms of acceptability, presentation and nutritional value. I have put acceptability and presentation first because, though most important, they are often factors that are overlooked in considering the problem. No matter how good or cheap a protein may be, it is no good to a child if he will not eat it, or if his mother finds it too much trouble to prepare, or if she thinks it would do him harm. The principal high protein foods at present being investigated in this way are skim milk powder and fish meal among the animal proteins, and soya bean and oilseed residues (cotton seed, sunflower seed, sesame, peanut and coconut) among the plant proteins. Plant seed proteins, it is well known, are often not ideal in amino acid make up — for example the usefulness of soya bean protein is limited by its low methionine content, and the same holds for peanut meal. These deficiencies can often be compensated for by using a mixture of proteins and among those that have been developed and are coming into use are Incaparina, in which 70% of the protein is from cotton seed, 25% from a maize-sorghum mixture, and 5% from yeast. This has been developed for use in South America. The Indian multipurpose food (MPF) is based on Bengal gram (sic) and peanut meal. In French West Africa a high protein food of millet, peanut meal and fish four has been developed while in Java a "milk" of sesame seed and soy bean extract is now very popular. It was not a success when first introduced in August, 1957, but after vanilla or chocolate flavouring was introduced the factory could no longer keep pace with the demand.
This is the beginning of a revolution in food technology. It is based on the formulation of a specification for a food designed for a particular nutritional purpose. Possible components of the food are limited by economics, which means, in practice, limited to materials hitherto regarded as industrial or agricultural wastes. Analyses of the ingredients are not enough to determine their suitability — they must be subject to determinations of digestibility and biological value. When they contain undesirable constituents, as for example the gossypol of cotton seed, methods of detoxication, that do not affect the nutritional value of the protein, must be developed. Finally, the mixture must be prepared in a form that will be acceptable in the area in which it is to be used. It will be of interest to some of you to note that, in a way, this is a partial reversal of the new idea that seized the imagination of many, some ten or twenty years ago. At that time there was concern in the advanced countries of the West that crop surpluses were likely to be a permanent feature of agriculture, and an effort to find uses for them as raw material for the chemical industry was made, and dignified with the name of chemurgy. Now we are looking for plant waste products from the chemical industry to use as foods.
The next stages in the fight to get more food to the people who need it must, of course, be on the production end of the process. Obviously our knowledge of how to increase yields per acre and to control pests is already far ahead of its application or, in many parts of the world, possible application at present. The knowledge we have is mainly applicable to soil and crops of the temperate zone and dependant on an advanced chemical industry to supply fertiliser and pesticides in very considerable quantities. Their use on a large scale in underdeveloped countries raises enormous problems of transport and of economics. Moreover, at present, we have not the basic knowledge required for their successful use on tropical soils — the debacle of the ground nut scheme was a convincing demonstration of this. It seems that any very considerable upgrading of agricultural production, in areas where techniques are primitive, must await new knowledge and an increased standard of living to supply the economic basis — there is in fact an obviously vicious circle in operation, for as the standard of living rises, population will rise, and the demand for increased production is only too likely to outrun the economic and technical ability to apply advanced methods of agriculture.
What ways out of the dilemma are there? One obvious one is the application of biochemical knowledge and research to the development of new sources of food, and the transfer of emphasis from one source to another. Let us first discuss new sources of food. One can be dismissed at once, synthetic food of the kind we now eat — proteins, fats and carbohydrates. It is a solution that may be feasible in the future, but that future is far distant, and to be of quantitative importance such a resolution can only come in the presence of abundant cheap power of the kind that controlled nuclear fusion may one day provide. This is not to say, the problems of synthesis of most of the vitamins have been solved, but, perhaps more important, there exists already processes for the synthesis of those amino acids which most often limit the biological value of many proteins — for example lysine and methionine. Already it is economic to use them as supplements for poultry feeding and, believe it or not, it is actually proposed to add lysine to bread in the United States — a reasonable proposition if it be assumed that in the United States man lives by bread alone!
It may also be worth while to enquire into the possible use of small easily synthesised molecules as a supplement to a normal diet. These include acetic acid, alcohol, glycine, alamine (alanine?), glycerol and succinic acid. Of these, alcohol is already used as an energy source by some — it supplies 5% of the energy for heavy work in the coal mines of Fife. Signs of poisoning only occur if its consumption rises above 30% of the total calorie intake. Probably compounds such as these could take care of about 10% of man's calorie requirements. With synthesis of fats, proteins and carbohydrates out of the question as a significant source of food, we must fall back on the sun's energy as the alternate source, and the 0.1% of it captured by plants as the proximate source.
The most important deficiency in most diets of the undernourished is protein, and an obvious first step is to place more importance than hitherto on protein content and yield as a crop characteristic, and it is, in fact, a recommendation of a recent FAO / WHO seminar "that agronomists should, when selecting food crops, think of yields in terms of protein per acre". It was also recognised by the seminar that it is unwise to extend the cultivation of roots, tubers and other starch foods because of their poor yield of protein. This was particularly so of cassava. It has also been suggested with much cogency that time spent in introducing temperate zone domestic animals into strange environments, to which they are not adapted, and then attempting to breed a better adapted variety, might be better employed in using the native animals as food sources and studying methods of managing, harvesting, and improving them. In Africa, for example, Darling has pointed out that the elephant, hippopotamus and antelope are all excellently adapted for this purpose, while the giraffe is less so, the buffalo likely to be difficult, and the rhinoceros impossible. The hippopotamus has the advantage over the others (in) that it feeds on water plants — a source at present not exploited by any domestic animal. I need hardly point out the possibilities of the kangaroo in Australia for producing meat from areas unsuitable for existing breeds of domestic animals.
Production of meat or fish in vastly increased amounts is undoubtedly a desirable aim and already FAO and others have increased considerably the amount of fish protein available in some undernourished areas by the introduction of fish farming methods. There is also much interest in further exploitation of sea fish, but the problems here are much more difficult. It must be borne in mind, however, that the demand for food will become so great that we shall no longer be able to afford the animal as a protein converter if it is possible to bypass it. An animal has a conversion efficiency of about 10%-15%; that is, it consumes (if a herbivore) up to ten times as much plant protein as it makes available to man in an edible form. If man were exclusively carnivorous, therefore, the percentage of the sun's energy available to him as food would be reduced from 0.1% to 0.01%, and if he eats carnivores, and not herbivores, to 0.001%. To grow a crop with protein of a high biological value and good digestibility, and feed it to an animal, and then eat the animal, is to waste nine-tenths of the food value of the crop. It has therefore been persuasively suggested that a solution to some of our future food problems lies in by-passing the animal completely and becoming much more vegetarian than we are today.
There have always been disadvantages in being vegetarian, though many races are mainly vegetarian perforce, and many individuals are by conviction. Nevertheless, man is not well adapted to a vegetarian diet. The carbohydrate nitrogen ratio is much higher in plants than in animals with much of the carbohydrate in an indigestible form encapsulating the protein. Herbivores have found two solutions to the problem of getting enough protein from plant food. One is to be inefficient and to make up for the inefficiency by eating far more food than necessary, digesting only part of it; the other is to be efficient, chew the cud, and allow time and micro-organisms to digest away the cellulose, thus enabling nearly all the protein present in the food to be digested. Man is not a ruminant nor can he afford the time to graze during most of the waking day. He is nowadays, however, sufficiently clever to consider the possibilities of mechanical cud chewing and externalised rumination. We also have techniques available for food preservation immeasurably superior to those of the primitive agriculturist, and, in addition, far more sophisticated methods for making unpromising or toxic materials palatable. The very narrow range of plants selected by early man was largely conditioned by factors now irrelevant. Food had to be edible after treatment by washing, grinding, fermenting or heating, and a premium was placed on products of low moisture content that were relatively stable on storage. These restrictions have meant, in practice, that only a few hundred out of the third of a million plant species have been domesticated and selected as food sources, and of these only a few dozen are of great importance today. It is high time that man began to review the potential usefulness of some of the unexploited species from two radical points of view — first. potential yield of protein per acre per year, and second, the economics of protein extraction by modern technological methods. The process has of course begun — attention has been paid to yeast as a source of protein and fat, but yeasts can only be a partial solution of the problem for, being saprophytic, they can be used only to transform waste products into useful products, and not to employ the sun's energy.
Chlorella, a unicellular microscopic green plant, has also been investigated as a source of food, and very impressive claims have been made for it. Many of these are based on its performance under optimal conditions of illumination, and the claims must be revised if field conditions of illumination are employed. It seems to me that the most promising possibilities lie in the extraction of protein from leaves. This is a process largely pioneered by Pirie at Rothamsted, and I was fortunate to be associated with the early stages of development. Leaves have a number of advantages as a source of protein. They can be crushed by simple machinery, the process of sap extraction necessitates very little in the way of equipment, and they contain a mixture of very many proteins. There is a very great deal to be said in favour of simple methods of extraction. If the process can be carried out by manpower, the power of a simple water wheel, or the very simple steam engines (which can be carried by two men) developed by the Rockefeller Institute, then a multiplicity of small scale plants is possible. Such a multiplication of small and perhaps relatively inefficient plants means that protein in this form can be produced in small amounts at the point of consumption, and produced frequently. The probable inefficiency of small scale operation seems likely to be far outweighed by the cost of collection and transport to a large plant, preservation of the product, and transport again to the site of consumption. The process is simple enough if the protein is to be consumed at once. Leaves are bruised, the juice is squeezed out of the mash, the protein precipitated by heat or acidification, and filtered off as a curd. Since the leaf protein is a mixture of very many proteins rather than a storage material, as it is in many seeds, the amino acid content appears likely to be much better balanced from a nutritional viewpoint, and to have a higher biological value than many seed proteins. There are, of course, disadvantages. Green food not in recognisable "salad" form seems strange and often repulsive to many people. If chickens are fed on it they tend to produce eggs with greenish contents that have no consumer appeal at all at present. However, as Pirie has pointed out, it could take some persuasion to get people to eat a preparation of the protein of milk precipitated by the action of bacteria growing in the milk, or by extract of calf stomach, and often further transformed by the action of blue and green fungi allowed to grow on the product, were we not familiar from childhood with cheese. Indeed, some of the more thoroughly rotted types of cheese are the gourmet's delight. The problem of acceptability has been mentioned before in relation to trials with the new protein rich foods developed by UNICEF and FAO, and will have to be met in the same way. Such a product is not necessarily to be envisaged as a main article of diet, of course 10g. a day in biscuits, soups or other forms would transform the nutrition over most of the world.
In the longer run, to solve some of the coming problems rather than those that are so clamant now, the village scale production would not be enough. For the future, and it is the near future, crops must be selected for high protein yield / acre / annum, which are suitable for leaf protein extraction, and grown under conditions of intensive mechanised agriculture, centrally processed, and the protein preserved and distributed. Not all leaves are suitable at present for the process, those with very high mucilage or tannin contents, for example, give very low yields. Many agricultural crops now grown have been shown to be easy to process, but, until a search has been made with the new criteria in view, no safe forecasts of yields of protein of high biological value can be given.
Research, related to that which is necessary, is already being done, for in Australia and other countries work is under way to find better plants for feeding stock — plants with a high nitrogen content plants which yield appreciable amounts through all seasons — plants suited to difficult conditions of soil, water or climate which have excluded the use of more conventional feeds. To go back to an earlier comment on the potential of the hippopotamus — the water hyacinth, a serious pest which blocks rivers and lakes with uncontrolled growth, is a candidate for harvest and processing. In its controlled multiplication it would have the advantage of occupying no land capable of being used by present methods.
Before finishing this talk I should like to examine briefly the possibility that the problem is not as serious as it is usually said to be, and what kind of natural check may be imposed if we do nothing about it. It has been said, and truly, that FAO's figures are based on optimal nutritional needs, and that, in some ways, they do not reflect nutritional needs in practice. There is truth in this comment. Obviously nutritional demands from individual to individual are not the same quite apart from the influence of their weight, sex and occupation. Some individuals will have a more frugal or efficient metabolic apparatus than others, some may require less of an essential amino acid than their fellow — there will in fact be a distribution of basic nutritional need around a mean. The nutritionist tries to specify a diet that will be adequate for all. If we agree that the desirable level should be adequate for all but one in a million, then those levels will be likely to be higher than if we set our sights at satisfying all but 1 in 1,000, or 1 in 100. The same argument can be put in another way — a given food supply may result in 50% of a population suffering undesirable side effects of a scant diet. At a higher level of nutrition — maybe 5% or 1% or .1% may suffer — how do we recognise these levels? Where do we draw a line? Much food could be saved in this way, but it is unlikely to be popular. Another argument that deserves consideration is that slight under-nutrition may be beneficial. Animal experiments, for example, have shown that cows fed respectively at 88%, 100% and 115% of the Scandinavian standard allowances prior to calving, and at the normal (100%) level thereafter, had life spans of 86.7, 80.5 and 67.2 months. Many other experiments tend to show that a high plane of nutrition in early life reduces longevity. If a longer life is regarded as individually desirable, it hardly solves the population problem, for it merely holds back the increase in food consumed for a short time. Other work on rats, has shown that overcrowding alone, in the absence of food shortage, results in rapid stabilisation of total population or even a catastrophic decrease. The causes appear to include a lower birth rate, a lack of maternal care leading to high infant mortality, and symptoms akin to acute neurosis. Similar effects are known in other animals. We do not know whether such mechanisms lie hidden in man. We may find out in the future if we avoid the more obvious checks of war.
I should now like to summarise the main points that I have made. First, there is an acute shortage of protein now over much of the earth. Second, this shortage is growing day by day — it is acute now and will be catastrophic very soon. Third, efforts are being made now to use protein sources otherwise ignored or discarded as useless for foods. The use of indigenous animals is one approach in areas where temperate zone domestic animals do not flourish. Another already in use is the use of oilseed residues — skimmed milk — fish powder. Distribution of new foods is useless without acceptance, and acceptance often means education first. The only solution that seems likely to be more than palliative in the future is the use of new plant foods. Plant foods, because we thereby avoid the 90% loss which animal conversion entails. The use of yeast and algae has been suggested, but both have serious disadvantages. The direct use of leaf protein is possible now, for, by the use of simple equipment, transport, storage and preservation problems can be largely avoided. In the near future the efficient exploitation of leaf proteins will entail modern mechanised methods on a large scale, and the development of the crops best suited for their use.
What does this programme need in terms of research? — it implies that we must start now on surveys or plants that might be of use in of extractable protein yield / area / year, and in terms of favourable balance in the amino acid composition of their crude leaf proteins as extracted. Work will be needed on detoxication methods, preservation methods and cooking methods all aimed at the preparation of acceptable protein supplements of high biological value. Of less but still great importance will be work on the development of uses for the by-products of the process — the use of the fibrous leaf residue as food for ruminants whether sheep and cows, or domesticated elephant and kangaroo. The use of the water soluble wastes from the process — already promising as a growth reaction for the fermentation industry. The use of lipids extracted from the protein cake to improve its keeping qualities. The field of work is enormous and its cultivation could transform many sections of plant biochemistry.
Finally let me reiterate that there are problems for the immediate future. In 1862 the world population was 1 billion, today it is 3 billion, in 20 years it will be 4 billion. Twenty years is in the lifetime of nearly all of us, in the working lifetime of the majority here. If we don't begin to do something now to prepare the solution for the future, many of us and certainly our children will have a pretty nasty mess to clear up. I began with an allusion to Tennyson and it's appropriate to end with another from "Locksley Hall 60 years after" — he is speaking of the world in the future —
"Every grim ravine a garden, every blazing desert till'd
Robed in universal harvest up to either pole she smiles
Universal ocean softly washing all her warless Isles."
He then refers to the alternative
"Warless? When her tens are thousands and her thousands millions then —
All her harvest all too narrow—who can fancy warless men?"
THE EARTH'S PHOTOSYNTHETIC YIELD
| Type of Land | Area km2 x 104 | g Carbon/m2 | Total C tons x 104 |
|---|---|---|---|
| Cultivated | 13.3 | 175 | 2,307 |
| Forest | 44.4 | 1,080 | 48,100 |
| Grassland | 36.9 | 89 | 3,286 |
| Wet Land | 3.3 | 690 | 2,280 |
| Desert, Tundra | 30.9 | 14 | 426 |
| Permanent Frost | 19.7 | 0 | 0 |
| LAND TOTAL | 148.5 | 380 | 56,400 |
| SEA TOTAL | 371.0 | 90 | 33,400 |
| WORLD | 519.5 | 173 | 89,800 |
Two ways of expressing the history of the total population of man. In the lower figure the population rise is shown over the last 10,000 years. In the upper both scales are logarithmic, enabling a period of a million years to be covered with emphasis on more recent times and early population "explosions".