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

SCHENKER.

STAPLETON.

It is plain from the foregoing results, that all the men of this group, like the members of the professional group, experienced no difficulty in reducing in large measure their rate of proteid metabolism. The intake of proteid food was steadily diminished, with a corresponding diminution in the extent of nitrogen metabolism. Take as an illustration the average daily output of nitrogen from April 13 to June 15, a period of sixty-three consecutive days:

AVERAGE DAILY EXCRETION OF METABOLIZED NITROGEN FOR THE LAST TWO MONTHS OF THE EXPERIMENT.

An excretion of 8.81 grams of nitrogen through the kidneys corresponds to the metabolism of 55 grams of proteid matter. Compare this average amount of proteid matter metabolized each day with the figures obtained during the preliminary period of ten days, when the men were living on their ordinary diet. Then, many of the men were excreting nitrogen at the rate of 17 to 22 grams per day. In a general way, we may safely say that all these men during the last two months of the experiment were living on about one-half the proteid food they were formerly accustomed to take.

Further, the average daily excretion of nitrogen for the preceding seventy-three days, i. e., from February 1 to April 13, was in most instances nearly, if not quite, as low as during the last two months of the experiment, so that we are certainly justified in the statement that these men—trained athletes, doing athletic work more or less strenuous—were able to practise during this long period marked physiological economy in the use of proteid food, equal approximately at least to a saving of full fifty per cent in proteid matter.

The individual tables must be carefully studied, however, in order to trace out the changes in detail in the rate of nitrogen metabolism, and in so doing much information will be obtained regarding modification in the excretion of uric acid, a matter to be discussed in another connection, later on. Further, it is interesting to note in the tables the changes in body-weight of the men. Some of the men, like Dr. Callahan, who were abundantly supplied with adipose tissue, lost very considerably in body-weight, but eventually came to a standstill, with establishment of body equilibrium, under the changed dietary habits. Some of the men reached this condition of equilibrium much more quickly than others. Dr. Callahan who suffered a large loss in body-weight—to his great gain, as he expressed it—dropped from 92.2 kilos to 83 kilos in two months, but from March 22 to June 15 his body-weight, while naturally showing fluctuation, did not fall again permanently.

What now was the amount of metabolized nitrogen per kilo of body-weight in these men toward the close of the experiment? Taking the average daily nitrogen excretion for the period from April 13 to June 15, and the body-weights of the men at this same period, as indicated in the accompanying table, we have the following figures:

These figures, with one exception, show as low a proteid metabolism per kilo of body-weight as was obtained with the soldiers on a prescribed diet, yet these men were athletes accustomed to vigorous muscular exercise, and likewise accustomed to the eating of relatively large amounts of proteid food. Theoretically, it might not be expected that these men would drop to as low a level as men who were not addicted to the consumption of excessive amounts of proteid foods, yet for two months, and practically for a period of four months, these University students easily maintained themselves at this lower level of nitrogen metabolism.

From April 26 to June 13, at the request of the students themselves, the daily diet was prescribed; not, however, as regards the quantity of food to be eaten, but merely as to its character. The men ate at the University Dining Hall, and it was a simple matter to have their table supplied with a special dietary. The following dietary was therefore prepared for their use.

It is not to be understood that the men took all that the daily list provided, but they made their selections from the menu, and in quantity took what they deemed necessary, or what satisfied their appetites. It may be added that the men were all well content with the variety provided and expressed themselves, many times, as better pleased with a simple dietary of this kind than with the heavier proteid foods of earlier days. It should be added that Dr. Callahan was compelled to be absent from New Haven during a large portion of the period covered by this dietary, hence his nitrogen excretions do not correspond in quantity with the nitrogen of the above rations.

Tuesday, April 26, 1904.

Breakfast.—Banana, boiled hominy with sugar and cream, coffee, rolls, butter.

Lunch.—Spaghetti, stewed tomatoes, potatoes, boiled onions, bread, butter, coffee, fried hominy with syrup.

Dinner.—Split-pea soup, fried bacon with French fried potato, spinach, bread, butter, stewed prunes, lettuce-celery-apple salad, cream puffs, coffee.