The results of our observations for Squad A are recorded in table 37 in grams of nitrogen per day in food and feces and in calories of energy per day in food, feces, and urine. The total and percentage of nitrogen utilized, and the total and percentage of energy available are also given. The differences in the utilization of nitrogen between the beginning and end of the experiment are extremely small, rarely amounting to more than 4 per cent. Hence it would be incorrect to state that there was a pronounced relationship between the amount of nitrogen in food and the nitrogen utilized.

Special attention should be called to the fecal nitrogen. While the character of the diet and the necessity for changing individual diets to maintain weight made it impossible to secure uniformity of nitrogen intake in all instances, we find that on October 8 to 12, the nitrogen in the intake was relatively constant for all men, that is, the values were all between 12 and 12.5 grams. The fecal nitrogen per day for these 12 men was as follows: 1.54, 1.35, 1.56, 1.33, 0.96, 1.22, 1.41, 1.22, 1.37, 1.33, 1.21, 1.02 grams, respectively; in other words, there was a maximum variation of 0.60 gram. This means, then, that when the same amount of food and essentially the same combinations of food, with practically the same nitrogen content, passed through 12 digestive tracts, the fecal nitrogen varied only from 0.96 to 1.56 grams. The period of study was, however, only 4 days. Since this particular test was begun on the fifth day of the restriction in diet, it is hardly probable that we can consider it as more than a normal digestion experiment, or an experimental verification of the earlier contention that under these conditions the digestibility of nitrogen, to use the older term, is the same with practically all healthy men.

1 Benedict, Carnegie Inet. Ween. Pub. No. 203. 1915. p. 232.

Table 37. - Nitrogen Utilized And Energy Available From Food In Digestion Periods - Squad A

The comparison of the digestibility in the later series after the men had been for some time upon the low diet is somewhat difficult, owing to the decidedly wide variations in the food ingestion. In fact, the nitrogen in food per day varied so widely with the different men after the middle of October that no considerable number of days can be selected to study the uniformity of the relationship between food nitrogen and fecal nitrogen. This will be implied from the percentage values for the utilization of nitrogen. But none of the figures show an abnormal nitrogen utilization. The low values, which fall to 82 and 85 per cent, are comparable with other observations, especially when it is remembered that the amount of animal protein was somewhat decreased in these observations.

The largest excretions of total nitrogen in the feces are those for Gar and Mon on December 10 to 15. These values correspond to their highest nitrogen intake other than in the first digestion period, that is, 13.20 grams with Gar, and 13.92 grams with Mon. That the presence of bran in the diet does not affect the nitrogen in feces is strikingly shown by the fact that Gar had no bran during the period of December 10 to 15 while Mon consumed 168 grams. Thus, one must be somewhat conservative in putting emphasis upon the presence of bran in the diet in considering the utilization of nitrogen. The conclusion can, however, be fairly drawn that the reduction in diet did not materially alter the digestibility of nitrogen.

The lowest utilization of nitrogen occurred with 7 of the 12 men in the digestion experiment of December 10 to 15, but an examination of the intake of nitrogen shows that this usually represented a period of high rather than low nitrogen intake, so that the low utilization of nitrogen is not coincidental with low nitrogen in the intake, as perhaps might be expected. In 5 cases, Vea, October 31 to November 4, Spe, November 12 to 18, Tom, December 10 to 15, Gul and Pec, January 14 to 30, we find the lowest utilization of nitrogen coincidental with the lowest nitrogen in food.

The available energy was, in all instances, highest during the first digestion period, that is, when the men were on normal diet. During the first digestion period the available energy averaged for the squad measurably above 92 per cent. Thereafter there was a distinct tendency for it to fall, values as low as 85 or 86 per cent being occasionally found. The absolute minimum was 84 with Moy and Kon on November 12 to 18. Seven of the men show the lowest available energy in the experiment of November 12 to 18. With all of the men the tendency is for the lowest available energy to occur with the minimum calories in the diet, this being in rather striking contrast to the evidence for the utilization of nitrogen.

The indigestible bran in the diet unquestionably raised perceptibly the true undigested food material in the feces, and undoubtedly accounts, in part at least, for the low value for available energy noted with some of these men. And yet it is a fact that, using the two illustrations cited in discussing the nitrogen data, Gar and Mon on December 10 to 15, when the energy of the food with each subject was about 3,000 calories, there is actually a slightly larger value for available energy in the case of Mon, although Gar had no bran and Mon had 168 grams. While this discrepancy is strikingly opposed to the general belief that the presence of bran in the diet would tend to lower the available energy, and one must realize that, after all, a relatively small proportion of bran is indigestible,1 nevertheless bran was in most instances an added food and contained a definite amount of un-hydrolyzable material. It would thus normally be expected to lower the energy available. In practically all studies on reduced diet low values for available energy are found. Those noted here are well within normal limits and we have no reason to question the influence of the restricted diet upon the digestive processes of these men.

One great difficulty, encountered in this research, was the tendency for the reduced diet to produce constipation, this making the separation of feces difficult. With Pec, whose abnormal defecation has been commented on frequently in this report, no accurate separation could be obtained between November 29 and December 10, although three or four attempts were made, and only approximate values are recorded in table 55. (See p. 334).