In this particular period of six days, the body was really gaining a little nitrogen, i. e., storing away a small amount of proteid for future use, although it may be granted that the amount was too small to have any special significance. During this period, the average daily intake of nitrogen was 6.4 grams, equal to 40 grams of proteid food. The average daily output of nitrogen through kidneys and excrement was 6.24 grams. The average daily output of metabolized nitrogen, through the kidneys, was 5.44 grams, corresponding to the breaking down of 34 grams of proteid material. Further, it should be stated that the total calorific value of the daily food during this period was less than 2000 calories. Let me add now a final balance period taken at the close of the nine months’ trial:

In this period of five days, the average daily intake of nitrogen was 5.86 grams, corresponding to 36.6 grams of proteid food. The average daily output of metabolized nitrogen was 4.92 grams, implying the breaking down in the body of only 30.7 grams of proteid material per day. The fuel value of the daily food, calculated as closely as possible, was less than 2000 calories. The body was essentially in nitrogen equilibrium, the minus balance being too small to have any special significance.

It will be instructive to consider next the actual character and amount of the diet made use of on several of these balance days:

March 21.

June 24.

June 25.

June 27.

It can be seen that there was nothing especially peculiar in these dietaries, aside from their simplicity, except that the quantities were small. Meat was not excluded; there was no approach to a cereal diet; there were no fads involved, nothing but simple moderation in the amounts of nitrogen-containing foods. Further, there was perfect freedom of choice; full latitude to consider personal likes and dislikes in the selection of foods; anything that appealed to the appetite could be eaten, with the simple restriction that the amount taken must be small. During the balance days, naturally, every article of food had to be carefully weighed and analyzed, which fact undoubtedly tended to limit in some degree the variety of foods chosen, since increase in the number of articles meant increased labor in analysis. Quite noticeable, however, was the extreme constancy in the nitrogen-content of the daily diet, even on those days when the food was not weighed. In other words, there had been gradually acquired a new habit of food consumption, and the individual, unconsciously perhaps, rarely overstepped the limits fixed by the new level of proteid metabolism. This is a fact that has been conspicuous in nearly all of our experiments, where freedom of choice in the taking of food has been followed; and is in harmony with the view that after a lower level of proteid metabolism has once been established, and the body has become accustomed to the new conditions, there is little tendency for any marked deviation from the new standards of food consumption.

With maintenance of body-weight, together with nitrogen equilibrium through all these months; and with health, strength, and mental and physical vigor unimpaired, there is certainly ground for the belief that the real needs of the body were as fully met by the lowered consumption of proteid food as by the quantities called for by the customary standards. Finally, it should be noted that this particular subject was small in weight, and hence did not need so much proteid as a man of heavier body-weight would require. In recognizing this principle, we may for future comparison calculate the nitrogen requirement of the body, on the basis of the present results, per kilo of body-weight. With the weight of the subject placed at 57 kilos, and with an average daily excretion of nitrogen amounting to practically 5.7 grams, it is plain that this individual was quite able to maintain a condition of equilibrium with a metabolism of 0.1 gram of nitrogen per kilo of body-weight. Translated into terms of proteid matter, this would mean a utilization by the body of 0.625 gram of proteid daily per kilo of body-weight. Regarding the fuel value of the daily food, we need not be more precise than to emphasize the fact that so far as could be determined, on the basis of chemical composition, the heat value of the food rarely exceeded 1900 calories per day. If we make a liberal allowance, for the sake of precaution, it would seem quite safe to say that this particular individual, under the conditions of life and bodily activity prevailing, did not apparently need of fuel value more than 2000 calories per day, which would correspond to 35 calories per kilo of body-weight.

Let us turn now to the second subject in this group, a man of 76 kilos body-weight, 32 years of age, and of strong physique. His active life in the laboratory called for greater physical exertion than the former subject, and consequently there was need for greater consumption of non-nitrogenous food, with the accompanying increase in fuel value of the day’s ration. As in the preceding case, there was no prescribing of food, but a gradual and voluntary diminution of proteid material. During the last seven months and a half of the experiment, the average daily excretion of nitrogen through the kidneys amounted to 6.53 grams, equivalent to a metabolism of 40.8 grams of proteid matter daily; a little more than one-third the minimal quantity called for by common usage. At first, the body-weight of the subject gradually fell until it reached 70 kilos, at which point it remained fairly constant during the last five months. That the quantity of food taken was quite sufficient to maintain the body in a condition of nitrogen equilibrium is apparent from the results of a comparison of income and outgo of nitrogen, as shown in the following table:

The average daily intake of nitrogen was 8.192 grams, equivalent to 51.2 grams of proteid food. The average amount of nitrogen excreted through the kidneys each day was 6.31 grams, corresponding to a metabolism of 39.43 grams of proteid matter. The plus balance of 0.380 gram of nitrogen per day shows that not only was the amount of proteid food consumed quite adequate to meet the demands of the body, but the latter was able to store up 2.3 grams of proteid per day. Regarding the character of the food taken by this subject, it should be stated that there was gradually developed a tendency toward a pure vegetarian diet. During the last seven months of the experiment, meats were almost entirely excluded. The diet voluntarily selected thus differed decidedly from that of the preceding subject in that it was much more bulky, contained a larger proportion of undigestible vegetable matter, and was richer in fats and carbohydrates, with a corresponding increase in fuel value. The exact character of the daily dietary is indicated by the following data of food consumption, on four of the days of the above balance period:

May 19.

May 20.

May 21.

May 23.

While the critic might justly say that these dietaries lack variety and would not appeal to a fastidious taste, there is force in the illustration which they afford of a simple diet being quite adequate to meet the wants of the body. Further, it should be emphasized that there is no special virtue in any of these dietaries, aside from their simplicity and low content of nitrogen. They represent individual taste and selection. Any other form of diet would answer as well, provided there was not too large an intake of proteid, and provided further the fuel value of the day’s ration was sufficient to meet the requirements for heat and work. Again, it might be said that with this latter subject the daily consumption of proteid food was considerably larger than with the first subject. This is indeed true, but it must be remembered that the second subject had a body-weight of 70 kilos during the last seven months, while the first subject weighed only 57 kilos. Obviously, with this marked difference in the weight of living tissue there must be a corresponding difference in the extent of proteid katabolism, and consequently a difference in the demand for proteid food.

As we have seen, the smaller subject for a period of many months showed a proteid katabolism equal to 0.1 gram of nitrogen, per kilo of body-weight, daily. The second and larger subject, on a totally different diet, for seven months and a half, metabolized daily, on an average, 6.53 grams of nitrogen. Taking the weight of the body at 70 kilos, it is readily seen that the nitrogen metabolized daily per kilo of body-weight was 0.093 gram, almost identical with the rate of nitrogen exchange found with the first subject. It is certainly very suggestive that these two individuals with their marked difference in body-weight, under different degrees of physical activity, and living on different forms of diet, with only the one point in common of voluntary restriction in the amount of proteid food, until a new habit had been acquired and a new level of proteid metabolism attained, should have quite independently reached exactly the same level of nitrogen exchange per kilo of body-weight. And when it is remembered that this was attained by the daily consumption of not more than one-third to one-half the minimal amount of proteid food called for by the dietetic customs of mankind, and with maintenance of all the characteristics of good health through this comparatively long period of time, there certainly seems to be justification for the opinion that the consumption of proteid food, as practised by the people of the present generation, is far in excess of the needs of the body. Referring for a moment to the calorific value of the food used by the second subject, in the last balance period, it is to be noted that the heat value per day averaged 2448 calories, as estimated on the basis of the chemical composition of the food. This would amount to 34 calories per kilo. Whether this figure is strictly correct is immaterial; it is certainly sufficiently so to warrant the statement that the needs of the body were fully met by an intake of food below the standards set by usage, and that maintenance of nitrogen equilibrium on a greatly diminished consumption of proteid food is possible without increasing the intake of non-nitrogenous matter.

Finally, as affording additional evidence, we may refer to a third subject in this group, a man of 65 kilos body-weight, 26 years of age, who for a period of six consecutive months maintained body-weight, nitrogen equilibrium, and a general condition of good health, with a proteid metabolism equal to 7.81 grams of nitrogen per day. During the last two months of the experiment, the average excretion of nitrogen per day amounted to 6.68 grams, corresponding to a metabolism of 0.102 gram of nitrogen per kilo of body-weight. This figure, it will be noted, is practically identical with the values obtained with the preceding subjects, calculated to the same unit of weight. Further, this third subject did not reduce his nitrogen intake by an exclusion of meat, but made use of his ordinary diet gradually reduced in amount. His daily consumption of proteid food averaged 55 grams, or 8.83 grams of nitrogen, and on this amount of proteid, without increasing the intake of fats and carbohydrates, he was quite able to do his work with preservation of physiological equilibrium.

Views so radically different from those commonly accepted can be made to carry weight, only by the accumulation of supporting evidence obtained under widely different conditions of life, and by methods which will defy criticism. It might be argued, and with perhaps some justification, that while professional men, with freedom from muscular work, may be able to live without detriment on a relatively small amount of proteid food, such a conclusion would not be warranted for the great majority of mankind with their necessarily greater muscular activity. We are confronted at once with the oft-heard statement that the laboring man requires more proteid food; he has a more vigorous appetite, and he must take an abundance of meat and other foods rich in proteid, if he is to maintain his ability as a worker. Note the statements already made in other connections regarding the food consumption of Maine lumbermen, of men on the football team, of trained athletes in general. These men consume large amounts of proteid daily, because their work demands it. If the demand did not really exist, they would not so agree in the use of high proteid standards, so runs the argument. The custom certainly does exist and is almost universally followed; men in training for athletic events deem it necessary to consume large amounts of proteid food. Custom and long experience sanction a high proteid diet, rich in nitrogen, for the development and maintenance of that strength and vigor that help to make the accomplished athlete. It is common knowledge to-day, however, that the energy of muscle work does not have its origin in the breaking down of proteid material, certainly not when there is an adequate amount of fat and carbohydrate in the diet. A high proteid intake must therefore be called for because of some subtle quality, not at present fully understood. It must not be subjected to criticism, however, because it is sanctioned by custom, habit, and common usage.

Still, I have ventured to experiment somewhat with a group of eight university athletes, all trained men, and with some surprising results. We have not space for details, but it may be mentioned that the men were young, from 22 to 27 years of age, and were experts in some field of athletic work. By a preliminary study of their ordinary dietetic habits, it was found that they were all large consumers of proteid food, with a corresponding high rate of proteid katabolism. One subject of 92 kilos body-weight, during ten days, showed an average daily excretion through the kidneys of 22.79 grams of nitrogen, implying a metabolism of 142 grams of proteid matter per day. On one of these days, the nitrogen excretion reached the high figure of 31.99 grams, corresponding to a metabolism of about 200 grams of proteid matter. Calculated per kilo of body-weight, this means a metabolism of 0.35 gram of nitrogen, or three and a half times the amount needed by the three professional men for the maintenance of nitrogen equilibrium. These subjects, with an intelligent comprehension of the point at issue, and with full freedom in the choice of food, gradually diminished their daily consumption of proteid material, at the same time cutting down very markedly the total consumption of food. The experiment extended through five months, and during the last two months, the average daily excretion of metabolized nitrogen of the eight men amounted to 8.81 grams per man. This corresponds to a metabolism of 55 grams of proteid matter.

Further, the average daily output of nitrogen through the kidneys during the preceding two months was in many cases nearly, if not quite, as low as during the last two months of the experiment. If we contrast this average daily exchange of 8.81 grams of nitrogen with the average output prior to the change in diet, it is easy to see that the men were living on about one-half the amount of proteid food they were formerly accustomed to take. Moreover, if the metabolized nitrogen for each individual, with one exception, is calculated per kilo of body-weight, it is seen to vary from 0.108 gram to 0.134 gram; somewhat higher than was observed with the older professional men, but not conspicuously so. Again, it is to be emphasized that the lowered intake of proteid food with these men was quite adequate to maintain their bodies in nitrogen equilibrium. We may cite a single case by way of illustration:

The daily intake of nitrogen during this balance period averaged 8.83 grams, corresponding to 55.1 grams of proteid food. The metabolized nitrogen eliminated through the kidneys averaged 7.58 grams per day, thus showing a daily average metabolism of 47.37 grams of proteid matter. With a body-weight of 63 kilos, this individual was maintaining equilibrium on a metabolism of 0.120 gram of nitrogen per kilo of body-weight. The fuel value of the day’s food as estimated did not exceed 2800 calories, thus substantiating the general statement that there is no need for increasing the fuel value of the food in any attempt to maintain a lower nitrogen level. This particular individual, in his choice of food, unconsciously drifted—as he expressed it—toward a simple vegetable diet, without, however, excluding meat entirely. The following four dietaries will serve to illustrate the character and amount of his daily food:

May 21.

May 22.

May 23.

May 24.

Here, again, we have dietaries not particularly attractive to every one, but they represent the choice of an individual who was following his own preferences, and like the preceding dietaries they are characterized by simplicity. In any event, they were quite adequate for the wants of the body, and their value to us lies in the proof they afford that a relatively small intake of proteid food will not only bring about and maintain nitrogen equilibrium for many months, and probably indefinitely, but that such a form of diet is equally as effective with vigorous athletes, accustomed to strenuous muscular effort, as with professional men of more sedentary habits. Further, these many months of observation with different individuals all lead to the opinion that there are no harmful results of any kind produced by a reduction in the amount of proteid food to a level commensurate with the actual needs of the body. Body-weight, health, physical strength, and muscular tone can all be maintained, in partial illustration of which may be offered two photographs of one of the eight athletes taken toward the end of the experiment; pictures which are certainly the antithesis of enfeebled muscular structure, or diminished physical vigor.