Starting at such a nutritional and health level as probably most people accept as their norm, it is now clearly possible (1) better to ensure a normally prompt development of the young, (2) to induce a higher level of adult vitality and accomplishment, and (3) materially to improve the duration as well as the quality of life, through the guidance of nutritional knowledge in the everyday choice and use of food. Three questions may have suggested themselves: (1) How conclusive are the data supporting such statements as those of the preceding paragraph?; (2) What are the grounds for confidence in the human application of the finding of laboratory animal experimentation in this field?; and (3) With all due reverence for individual human lives, will a longer‐lived population be an advantage? Each of these questions is worthy of a much fuller answer than the space here available permits; and could be answered with much ampler evidence and explanation, but for the present need of extreme condensation. Statistical analysis of the objective, numerically recorded data of laboratory‐controlled experiments shows, at all stages of the life cycle, nutritional improvements upon the initial norms with measured differences so manifold greater than their probable errors as to establish these findings with higher degrees of scientific certainty than probably attach to most of the unquestioned facts of physiology. The least‐expected of the new findings, namely, the extension of the normal adult life‐expectation, is objectively established with 100‐fold greater degree of statistical convincingness than the accepted canons of scientific criticism call for to justify the characterisation of such a finding is “undoubted.” The basal dietary of these experiments is representative of the food supplies upon which a large proportion of our people subsist; and the animal species chiefly used for the full‐life, successive‐generation experiments above mentioned is the rat, chosen primarily because of the many and close resemblances of the chemistry of the nutrition of that species and our own. The only known significant differences are with respect to ascorbic and nicotinic acids; and toward both of these the human species is much more responsive to the level of dietary intake than is the rat. Critical study reveals no reason to discount the above‐noted laboratory findings because of species difference; but, on the contrary, shows strong scientific evidence that the indications obtained from the experiments with rats are well within the probabilities of the nutritional improvement of human lives by intelligent use of our everyday foods. Such nutritional improvement results not only in longer life but also in the living of our lives upon a higher level of health and accomplishment throughout. The “extra time” is not added to the period of senility. It is inserted in the period of the prime, making this a longer fraction of the life cycle. Thus the nutritional improvement brings, to speak in human terms, both a larger number and a larger percentage of years of full accomplishment, and economic and social value, with a smaller proportion of years of dependency. Space does not permit the discussion here of the very real advantages, to the individual, to the world of industrial affairs, and to the nation, of an earlier attainment of full capacity and also a postponement of the onset of old age. How to extend the benefits of the newer knowledge of nutrition, as widely and as promptly as possible is both an economic and an educational problem. If space permitted, an abundance of statistical evidence could be assembled to show: (1) that, independently of educational opportunities, the families with better per capita purchasing power tend to provide themselves with nutritionally better food supplies; and (2) that also, among families exercising the same purchasing power in the same markets, some provide themselves with dietaries which are nutritionally excellent, others only good, and still others only fair. Much can be (and in many places is being) gained either by direct economic measures to increase the purchasing power of low‐income families whether by increase of money income or by making available to them larger supplies of protective foods at lower prices; or by widespread teaching of the nutritive values of foods and the influence of nutritional wellbeing upon health and earning‐power. Needless to say, the communities which have good use of both of these means of improvement may expect to reap the largest benefit. In an unbiased economic view everyone can see that there is opportunity for enormous benefit in using the new knowledge of nutritive values to guide the investment of the many billions of dollars that are annually spent in this country for food; and especially when the choice of food is now known to have greater and more far‐reaching effects upon health and earning power than has hitherto been supposed. But how often bias enters to cloud the economic view! Attempts to teach a more scientific investment of money in food are apt to meet a “vested interest” attitude of resentment from many purveyors of things which science cannot recommend for a higher place in consumers' budgets. And perhaps an even larger number of people “object on principle to,” or subconsciously react against, any attempt to teach discrimination of consumer demand, and any form of governmental paternalism or further extension of “government into business.” In addition to all the bias of an economic or political sort, tradition in itself retards change, especially in matters which come so closely home as does the family food supply. And in the domain of food, as one of the wisest students of nutrition has said, tradition tends to accumulate prejudices quite as often as truths. These and other causes tend somewhat unduly to caution in public teaching of the everyday use of the newer knowledge, which in terms of foods as bought and eaten is: Give fruits, vegetables, and milk in its various forms (including cheese, cream, and ice‐cream, if desired) a larger place in the dietary and food budget. This can be done without “cutting out,” and without too drastically “cutting down,” any other articles of food. As the Nestor of the new knowledge of nutrition has consistently taught: If we cat what we should, we can at the same time eat what we like. Another question sometimes arising is, How can we feel confident of the practical application of present nutritional knowledge when we admit its probable incompleteness by recommending further research? The present writer's answer is that some findings of such far‐reaching importance that their everyday application ought not to be postponed are conclusively established, and the practical advice above suggested is based upon these and is permanently valid. More elaborate and detailed dietary recommendations may well await the findings of such further researches as are briefly suggested below. Both further research and fuller application, neither delayed by waiting upon the other, should be strongly emphasised, especially in view of the present and impending situation. There should be prompt and wide dissemination of present knowledge at all teaching levels. And nothing is so stimulating to education as that research in the same field be actively productive at the same time. The best way to get a hearing, even for the findings now conclusively established, is to have some related new findings to tell. If made in large numbers, with great care, and on a comprehensive plan, further researches with natural foods as the experimental variables might be of great value. More accurate knowledge of the quantitative distribution of certain of the mineral elements and vitamins in foods can be sought with greater assurance of clear‐cut findings, and with certainty that these data will function both in the advancement of science and in the service of human welfare. There is also a field for much valuable research in the measurement of the nutritional availabilities of the mineral and other nutrients of the different articles and types of food, more especially by experimental methods which comply with the actual conditions of normal nutrition. With more precise knowledge of the nutritive values of a wider range of foods, it becomes increasingly practicable to ensure excellence of nutrition without sacrifice either of personal preferences in food selection or of the economic advantages which market fluctuations and seasonal conditions offer. Fortunately, most seasonal food crops are at their best when they are also at their cheapest. The fuller our knowledge of nutrition, the less we need depend upon diversification, but the better we are prepared to gratify a taste for it. The newer knowledge of nutrition is friendly to the fact that “eating has a great vogue as an amusement,” and several foods formerly regarded as luxuries are now seen to be good nutritional investments. The science of nutrition does not seek the sanctification of spinach: it looks with much more favour on many of the things that we find most fun in eating. The new knowledge helps in meeting the problems of both war‐time and peace‐time food supplies; and the findings of further research will doubtless help us all still further to harmonise our appetites and aspirations—to know how to eat both what we want and what will make us most efficient. Both for completeness of scientific explanation and to establish the boundaries of advantageous practical application of the findings, further research is needed even upon two of the three factors which, as mentioned in an earlier section, have already been studied more fully than others by our recently developed methods. As opportunity permits, similar studies should also be made of the long‐time effects of different levels of intake of each nutritionally essential amino acid, mineral element, and vitamin. Meanwhile, the factors which have already been found to be of outstanding importance in experiments upon the entire life cycle should now be studied by similar methods but with starting‐points at different ages so as to ascertain the influence of initial age upon the potentialities for nutritional improvement of the life history. In the planning of all such studies the world‐wide present interest in efficiency and preparedness will tend to give priority to those researches which bear most directly upon problems of the attainment of the fullest fitness, from what‐ever initial age, and the maintenance of optimal capacity for service. Fortunately, such advances of knowledge will service both science and the nation well, however long or short the war, and whatever its aftermath may be. Studies in nutritional rehabilitation deserve also a well‐considered place in the general programme for bringing the new knowledge into the service of all the people. Between the obvious cases of specific deficiency diseases and, on the other hand, the people whose physique and efficiency are within the zone of our present norm, too many even of our American people (and doubtless a higher proportion in most other countries) are handicapped, though we may not know exactly how and why. Many of these people can be rescued from individual and family frustration, and incalculably enhanced in economic and social value to the community and nation, by “enough of the right kinds of food”; and just what this means in more precise terms, how the greatest good can be accomplished with most promptness and efficiency, are problems within the scope of the present‐day methods of research in the chemistry of nutrition. Moreover, the same general type of research reveals good scientific probabilities of improving the chemistry of the internal environment, and thus enhancing the efficiency, of people who are already quite fortunately healthy and efficient.
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