Twenty‐three years ago the most frequently met among many slogans was “ Food Will Win the War.” To‐day our food problems are fully as important to our defence; but they present many new aspects. Then our prime duty was to save food : now it is to consume food in the way most conducive to fitness. Our knowledge of nutrition has advanced so rapidly that much of it is too new to have been assimilated into our everyday thought and practice. Yet it is precisely as guidance to everyday use of our familiar foods that the newest knowledge of nutrition can be of most benefit: of benefit both to the one‐third of our people who are officially declared “ ill‐nourished,” and to the great majority of the rest of us as well. For while finding that much of our previously baffling disease and frustration is due to shortage of certain nutritional factors in the food supply, research has also shown that a more scientifically guided use of our everyday foods constitutes a sort of superior chemical engineering of our own mechanisms which can increase the vitality and efficiency even of those people who are already healthy and efficient. The relations of nutrition to the functioning of the mind are, of course, more difficult of controlled investigation and not yet as objectively demonstrable as to the effects of food upon bodily functions and length of life. But careful research is now showing that even within the range of fully normal conditions, our daily food choices have much more important effects than science ever previously supposed upon that internal chemistry that directly environs and conditions all our life processes. The blood is the great mediator of this internal environment, and the same blood circulates through the brain as through all the other organs of the body, bringing its help or its hindrance to both mental and muscular activities. True there is much which remains to be clarified by further research; but the already established findings, of recent and current nutritional investigation, need only to be more widely known and used in order to make our people much stronger for the defence of our civilisation, and for its permanent advancement when the emergency has passed. In our “ intellectual climate ” of the moment there is still a good deal of inertia because the newest knowledge is not yet sufficiently understood, while at the same time the new view is perhaps being over‐coloured by some writers. This paper therefore does not seek to add more assertions; but rather to review objectively the evidence on what the Council of National Defence has announced as one of our present‐day needs, “ to make the American people nutrition‐conscious in terms of the nutritional science of to‐day.” Nutrition presents three major aspects : (1) that in which food serves as fuel to supply energy for the activities of the bodily machine; (2) that of the assimilation of certain food constituents into structural material first for the growth and later for the upkeep of the body tissues; and (3) the utilisation of food substances either directly or indirectly to serve the body in those self‐regulatory processes by which it maintains its relatively “ steady states ” or essential internal environment. It is in its energy aspect that nutrition has most fully arrived at the status of an exact science. Expert opinion is well agreed on the fundamental principles of the energy transformations in the body, on the values of the foodstuffs as sources of energy, and on at least the broad lines of theory as to the influence of different bodily conditions in determining the energy need. On the latter points, especially, many laboratories are actively engaged in increasing the precision of present knowledge, and at least three well‐endowed nutrition laboratories—those of the Carnegie Institution, of the Russell Sage Institute, and of the Rochester University Department of Vital Economics—are devoting their resources especially to the perfection of the energy aspects of nutritional knowledge. The protein aspect of nutritional research has also reached a relatively mature status with well‐defined objectives. Among many other laboratories working in this field, that of the United States Department of Agriculture is giving special attention to the purification and description of the proteins themselves; and the laboratory of physiological chemistry of the University of Illinois is very actively investigating the nutritional relationships of the individual amino acids, with the generous support of the Rockefeller Foundation. We may look forward with confidence and great gratification to a presumably fairly near future in which this aspect of nutritional need can be stated quantitatively in terms of ten individually indispensable amino acids. The catalysts which make the chemical processes in the body go fast enough to support life overlap and in a measure integrate the subject matter divisions of the chemistry of nutrition. They function in the energy aspect; and in their own chemical constitutions they are derivatives of proteins (or their amino acids), mineral elements, and vitamins. This very active field of research is quite as frequently classified with general biochemistry as with nutrition. Until its current era of “ newer knowledge,” the chemistry of food and nutrition had for several decades faced the dilemma that foods could be analysed as elaborately, and their composition accounted for with as close an approach to one hundred per cent., as other natural materials; and yet nutrition could not be sustained with pure mixtures of the substances that the analyses revealed. Seeking deeper insights, chemists broadened their research methods to include the systematic use of feeding experiments with laboratory animals, carried on with as careful attention to accuracy of controls as in other experimental researches in the exact sciences. This extension of method in chemical research has been rewarded with a rapid series of discoveries of substances which are essential to our nutrition, but whose very existence was, until recent years, either entirely unknown or only vaguely apprehended. Neither in chemical nature nor in nutritional function do these substances have much in common with each other. That they came to be called by the group name vitamins was not the result of their being naturally related, but rather of the two circumstances, (1) that they were all discovered through the use of the same development of research method, and (2) that the discoveries of their existence and importance followed each other too rapidly for physical isolation and chemical identification and nomenclature to keep pace. The latter, however, are steadily catching up, and in several cases new names, which are individually distinctive of either the chemical structures or the historic associations of the substances, have been coined and are coming into general use.
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