Physiological economy in nutrition, with special reference to the minimal proteid requirement of the healthy man / an experimental study

by R. H. Chittenden

It is quite evident from a study of the results obtained in the foregoing experiments that young, vigorous men of the type under observation, trained in athletics, accustomed to the doing of vigorous muscular work, can satisfy all the true physiological needs of their bodies and maintain their physical strength and vigor, as well as their capacity for mental work, with an amount of proteid food equal to one-half, or one-third, that ordinarily consumed by men of this stamp. As the results show, all these men reduced their rate of proteid metabolism in such degree that the amount of nitrogen excreted daily during the period of the experiment averaged 8.8 grams, implying a metabolism of about 55 grams of proteid matter per day.

In other words, these athletes were able to reduce their nitrogenous metabolism to as low a level as many of the men of the professional group and of the soldier group, and this with not only maintenance of health and strength, but with a decided increase in their muscular power.

Metabolized nitrogen per kilo of body-weight for all these men, with one exception, during the experiment amounted to 0.108 to 0.134 gram per day, fully as low as was obtained with the members of the soldier detail on their prescribed diet. It is clear, therefore, that physiological economy in nutrition is as safe for men in athletics as for men not accustomed to vigorous exercise. There is obviously no physiological ground for the use of such quantity of proteid food, or of total nutrients, as the prevalent dietary standards call for.

The athlete, as well as the less active man (physically), or the professional man, can meet all his ordinary requirements with an intake of proteid food far below the quantities generally consumed, and this without increasing in any measure the amount of non-nitrogenous food.

IV. THE SYSTEMIC VALUE OF PHYSIOLOGICAL ECONOMY IN NUTRITION.

It is one of the axioms of physiology that the majority of the diseases of mankind are due to, or are connected with, perversions of nutrition. General or local disturbances of metabolism are broadly responsible for disease, and with a due recognition of this fact it may be well to consider more specifically whether greater economy in the consumption of food, i. e., a restriction of the daily diet to amounts more commensurate with the physiological needs of the body, may not be of value in preventing disease, or prove of use in combating disease when the latter has manifested itself.

Broadly speaking, the extent and character of the metabolic processes of the body are dependent in large measure upon the amount and character of the diet. Further, it is equally certain that the chemical composition of the blood and lymph is quickly affected by the amount and character of the food materials absorbed from the alimentary canal. Even in the matter of secretion of the digestive juices, we have learned, through the recent experiments of Pawlow, that the chemical composition and solvent action of these fluids may be modified by the amount and character of the food fed. How much more, then, may we expect the intricate processes of cell and tissue metabolism to be modified by changes in the chemical composition of the blood and lymph that bathe them.

Further, recognizing as we must the extreme sensitiveness of the central and peripheral parts of the nervous system to changes in the composition of the blood, we see suggested indirect ways by which metabolism, both general and local, may be modified by influences exerted upon the nervous system, whereby the nutritive condition of individual structures may undergo change. Vasomotor influences, controlled as they are by nerve fibres, which in turn are sensitive to the conditions of their environment, likewise indirectly affect the rate and character of tissue metabolism; a fact which may serve to emphasize the many ways whereby the metabolism of an organ or tissue may be modified through the primary influence of a diet which, controlling in a measure the volume and character of the circulating blood and lymph, must of necessity exert an influence more or less extended.

The one factor above all others that tends to increase the extent of proteid katabolism is the amount of proteid food ingested. Increase in the amount of the albuminous foodstuffs is at once, or speedily, followed by an increase in the output of nitrogenous waste products, the latter constituting a good measure of the extent of proteid metabolism going on in the body. We have been taught to believe that the healthy adult under ordinary conditions of life needs for the maintenance of health, strength, bodily and mental vigor, about 118 grams of proteid food daily. This amount of albuminous food, if metabolized, means at least 16 grams of nitrogen in the urine, in the form of urea, uric acid, creatinin, purin bases, and other nitrogenous products more or less closely related. Under the stress of modern conditions and following the dictates of an acquired taste, the daily intake of proteid food in many individuals at least far exceeds the above figures, with an increase of proteid katabolism equal to 18 or more grams of nitrogen in the 24 hours’ urine.