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

by R. H. Chittenden

We can point to various persons who, for periods ranging from six months to a year, have metabolized daily 5.5 to 7.5 grams of nitrogen instead of 16 to 18 grams, i. e., they have subsisted quite satisfactorily on an amount of proteid food daily, equal to one-third or one-half the amount ordinarily considered as necessary for the maintenance of health and strength, and this without unduly increasing the amount of non-nitrogenous food. Further, our observations have shown that with this great reduction in the consumption of proteid food, with corresponding diminution of proteid katabolism, body-weight can be maintained at a stationary figure, after the body has once adjusted itself to the new conditions. Moreover, there is marked increase in physical strength as demonstrated by repeated dynamometer tests on many individuals, which may perhaps be ascribed to the greater freedom of blood and lymph, as well as of muscle-plasma, from nitrogenous extractives. Lastly, we have failed to find any falling off in physical or mental vigor, any change in the hæmoglobin-content of the blood, or in the number of erythrocytes. In fact, all our observations agree in showing that it is quite possible to reduce with safety the extent of proteid katabolism to one-third or one-half that generally considered as essential to life and strength. In other words, there is perfect safety in a lowered proteid metabolism, and we are inclined to raise the question whether a daily diet containing one-half, or even less, the amount of proteid food ordinarily consumed does not come nearer to the normal and natural requirements of the healthy body than the more elaborate standards we have gradually adopted.

Here, then, we have suggested a radical change in diet which experiment shows is perfectly safe, and we are disposed to urge that there is great systemic value, both in health and in many forms of disease, in such a change. It is obvious, as previously stated, that the smallest amount of food that will serve to maintain bodily and mental vigor, keep up bodily strength, and preserve the normal powers of resistance to disease, is the ideal diet. Any excess over and above what is really needed for these purposes imposes just so much of an unnecessary strain upon the organism. It entails a wasteful expenditure of energy that might better be preserved for future emergencies. It imposes upon the excretory organs the needless labor of removing waste products which could well be dispensed with, to say nothing of the possible physiological action of these products as they circulate through the body.

Dr. Walker Hall,[51] in his interesting article in “The Practitioner” on “Metabolism in Gout,” states that “under normal circumstances a man weighing eleven stone and performing average work requires twenty grams of nitrogen and three hundred grams of carbon per day.” This statement is in perfect harmony with generally accepted views, but I should like to emphasize the fact that all of the twenty-six men we have been experimenting with at New Haven, representing different types, ages, and degrees of activity, have been able to maintain health, strength, and vigor, from six months to a year on a daily quantity of nitrogen equal to one-half, one-third, and even one-quarter the amount of this so-called necessary twenty grams. Further, nitrogenous equilibrium was easily maintained on such quantities of proteid food, and, as before stated, there was great gain in physical strength. Are we not justified, therefore, in raising the broad question whether such a radical change in diet as these facts suggest might not be of systemic value in gout, and especially in cases where there is a predisposition to gout. Speaking as a physiologist, the writer is strongly of the opinion, based in part upon his own observations and in part upon both the voluntary and unconscious testimony of others, that there is possible great gain to the gouty and rheumatic individual by a practice of physiological economy in nutrition.

Physiological economy, as the writer defines it, is not prohibition, but temperance. Moderation in diet, especially in the taking of proteid foods, means a great saving in the wear and tear of the body machinery. It must presumably mean greater freedom from many diseases in which individual organs, such as the liver and kidneys, are frequently involved. It suggests, likewise, greater freedom from many disturbances of general metabolism which eventually terminate in a perversion of nutrition, so marked as to constitute a serious condition of disease. More specifically, lowered proteid metabolism means diminished introduction and diminished formation of nitrogenous products of the purin type, such as xanthin, hypoxanthin, guanin, adenin, etc., as well as of other nitrogenous bodies less clearly defined. Consequently, we have as one of the results of such a systemic change in diet a decreased formation of uric acid, or at least a diminished output of uric acid through the urine.

Obviously, a lowered proteid intake means, in some measure at least, a decreased consumption of meat and similar products more or less rich in free and combined purin bases. This quite plainly must result in a diminished production of uric acid, but the writer is strongly of the opinion that we do not as yet possess sufficiently full knowledge regarding all the ways in which uric acid results in the body. It is true, we differentiate between endogenous and exogenous uric acid, and further, we understand quite clearly that variations in the intake of free and combined purin bases exercise a potent influence upon the output of uric acid through the urine. We still lack, however, concise information as to the various ways in which uric acid may be produced, and its ultimate fate in the body. This is well illustrated by a recent paper from the Marburg laboratory, in which Kutscher and Seemann[52] point out the possibility of a production of uric acid in the animal body synthetically, and likewise suggest that uric acid may be utilized for the formation of nuclein bases, i. e., a reversal of the oxidative process by which uric acid results from the ingestion of free or combined nuclein bases, suggesting indeed the possibility of uric acid and the nuclein bases being produced from each other, according to the circumstances. Thus, when nucleins or free purin bases are taken with the food, the organism may utilize this material at once in the synthesis of nucleins for the use of the body cells. There is no need of a reduction of the formed uric acid to nuclein bases, and consequently there is an increased excretion of uric acid through the urine, but this does not result from a direct transformation of the ingested purin material into uric acid, but is the result of a sparing of the already formed uric acid. The nuclein bases thus act as sparers of uric acid. This view explains, according to Kutscher and Seemann, why feeding with nuclein bases increases the output of uric acid, and feeding with uric acid—a sudden overflow of uric acid into the circulation—is followed, as a rule, by an increased elimination of urea, the uric acid being thus transformed by energetic oxidation. This hypothesis is brought forward not merely because it is an interesting suggestion, but mainly because it illustrates that we do not as yet know fully all the steps in the production of uric acid, nor do we know how far the uric acid we find and determine in the urine is a measure of the formation of uric acid in the body.

Taking our knowledge on these matters as it stands to-day, however, we find by experiment that lowering the intake of proteid food, with its consequent corresponding diminution in proteid katabolism, is followed at once by a marked decrease in the output of uric acid. Let us consider a few of the data obtained in our experiments. The first case I will refer to is that of a college athlete (Callahan). For a period of ten days on his ordinary diet, the average amount of nitrogen in the urine per day was 22.8 grams, equal to the metabolism of 142.5 grams of proteid food. During this same period the average daily output of uric acid was 1.103 grams. For the following four months and a half, on a more restricted diet, with a marked cutting down of the proteid food, but with no exclusion of meat, the average daily output of nitrogen through the urine was 9.04 grams. In other words, for this period of over four months the extent of proteid katabolism was reduced considerably more than 50 per cent. The average daily output of uric acid for this same period was 0.624 gram, equal to a reduction of about 40 per cent from his normal excretion.

Another college athlete (Stapleton), on his normal diet, showed an average excretion of nitrogen through the urine per day, for ten days, of 19.70 grams, while the daily average excretion of uric acid for the same period was 0.893 gram. On a more restricted diet, with diminished proteid katabolism, the daily average excretion of nitrogen through the urine for a period of over four months was 11.06 grams, while the daily average excretion of uric acid for the same period fell to 0.699 gram. In the first of these two cases the average daily ratio of uric acid to total nitrogen during the period of lowered proteid metabolism was 1:14. In the second case the ratio was 1:16.

A third college student (G. W. Anderson), on his ordinary diet, excreted through the urine for a period of nine days 17.17 grams of nitrogen as the daily average, while the average daily output of uric acid for the same period was 0.956 gram. On the more restricted diet of the next four or five months his average daily excretion of nitrogen fell to 9.37 grams per day, while the average daily excretion of uric acid was reduced to 0.632 gram. On his ordinary diet, the ratio of uric acid to nitrogen was 1:18, while later with the diminished proteid metabolism the ratio was 1:14.

Turning to another class, viz., professional men, reference may be made to the writer, whose average daily nitrogen excretion through the urine for a period of nearly nine months was 5.699 grams, corresponding to the metabolism of 35.6 grams of proteid per day. During this same period of nearly nine months the average daily excretion of uric acid amounted to 0.392 gram, the ratio of uric acid to total nitrogen being 1:14. In passing, it may be repeated that the subject of this experiment succeeded in maintaining a constant body-weight, and he further avers that in physical and mental vigor he can find no evidence of deterioration, although the amount of proteid food consumed daily during this long period was less than 40 grams per day. Further, he was in nitrogenous equilibrium during this period, although the nitrogen metabolized daily amounted to only 99 milligrams per kilo of body-weight. Another case in this same group may be mentioned, principally because the subject for over a year became a vegetarian, abstaining from all meat. During the last nine months, this man (Beers) eliminated 8.28 grams of nitrogen through the urine as the daily average, indicating a metabolism of 51 grams of proteid material per day. During this same period, the average daily excretion of uric acid was 0.349 gram, the ratio of uric acid to total nitrogen being 1:23.