In an earlier publication on fasting,1 four food experiments with mixed diets were reported following fasts of 4 to 7 days in duration. These have already been discussed in our consideration of the basal metabolism (see pages 55 to 60), but are abstracted here, as they give further information regarding the influence of a mixed diet. As stated in the previous discussion, our earlier plan was to use fasting values as base-lines, and then note the increment in the metabolism due to subsequent food ingestion. When we attempted to select a base-line, a number of serious objections to this at once presented themselves. In the first place it was noted that the total metabolism for the day almost invariably decreased gradually as the fast progressed. An examination of the data in table 248, which presents in abstract the four food experiments referred to, together with the preceding fasting periods, shows that in practically every instance there was a tendency for the heat production to decrease as the fasting continued. This tendency is most clearly shown in the fasting periods with S. A. B. on January 8 to 11, 1905, and January 28 to February 2, 1905. It so happens that in the long fasting experiment of 7 days with S. A. B., the metabolism was essentially constant on the first 4 days; on the fifth day there was a sudden fall of over 100 calories, followed by another fall of 100 calories on the sixth day. In the experiment with A. L. L., the variations in the metabolism are somewhat pronounced; as a matter of fact the value is the same on the fourth day as on the first. Certain variations in these values from day to day may be in part accounted for by variations in muscular activity, although the attempt was made to have like activity on all days.

Table 248. - Heat Production Of A. L. L. And S. A. B. Without Food And After The Ingestion Of A Mixed Diet

[Values per 24-hours (7 a. m. to 7 a. m.)]

1Benedict, Carnegie Inst. Wash. Pub. No. 77, 1907. 2See table 7, p. 56.

3See table 8, p. 57. 4First day not included because of work done on bicycle ergometer.

5See table 9, p. 58. 6See table 10, p. 59.

In the food experiment with A. L. L., the diet averaged 1,615 grams of a modified milk and 6 grams of plasmon per day, the total daily intake being 1,621 grams. This had a total fuel value of 2,502 calories, of which 9 per cent came from protein, 79 per cent from fat, and 12 per cent from carbohydrates. In the food experiment with S. A. B., January 11 to 12, 1905, the food taken per day was 1,253 grams of a modified milk and 106 grams of orange juice, the daily amount being 1,359 grams. The total fuel value was 1,698 calories, of which 9 per cent came from protein, 73 per cent from fat, and 18 per cent from carbohydrates. In the second food experiment with S. A. B. (February 2-5, 1905), the subject ate per day, 1,200 grams modified milk, 123 grams apples, 313 grams orange juice, and 35 grams graham crackers; the daily total was 1,671 grams. The total fuel value was 2,078 calories, of which 8 per cent came from protein, 65 per cent from fat, and 27 per cent from carbohydrates. In the last food experiment with S. A. B. (March 11-14, 1905), the food taken per day was 650 grams modified milk, 123 grams apples, 178 grams whole wheat breakfast food (dry), 10 grams gluten bread, and 313 grams orange juice, a daily total of 1,274 grams. The total fuel value was 1,788 calories, of which 9 per cent came from protein, 37 per cent from fat, and 54 per cent from carbohydrates.

The amounts of food ingested were unfortunately not satisfactory, the fuel value of the food intake being determined solely by the appetite of the subject on the first day of food following the fast. The diet for the subsequent days was the same as that on the first day, the amounts varying only a few grams, if at all. The fuel value of the food in the experiment with A. L. L. was considerably above the 24-hour maintenance requirement. In the first experiment with S. A. B., it was essentially that of maintenance, in the second experiment with this subject it was measurably above maintenance, and in the third experiment it was above the maintenance requirements during the fasting, but practically the same as the need for maintenance during the food period.

We thus consider here an influence of food upon the fasting metabolism which is not represented simply by the increment above a basal value obtained by averaging all of the fasting days, as the basal value may change and in certain circumstances does change considerably during the fast. This was shown clearly in the fasting experiment of 31 days carried out in the Nutrition Laboratory.1

It hardly seems justifiable to attempt a computation of the fasting values obtained in these four experiments on the basis of per kilogram of body-weight or per square meter of body-surface. There were, to be sure, measurable losses in weight which were probably largely due to a loss of water from the body, especially in the earlier part of the fast. That there was a considerable loss in body-surface or of active heat-producing organized tissue is hardly conceivable. After the ingestion of food there were undoubtedly slight gains and losses in weight, but this discussion considers the organism as a whole, for only days with and without food are compared and no attempt is made to compare results obtained with different individuals.

Even in the first experiment recorded in table 248 (that with A. L. L.) the actual value of the base-line may be seriously questioned. An average value for the fasting periods would be not far from 2,025 calories. On this basis it can be seen that the ingestion of food, with a fuel value of 2,502 calories, barely increases the metabolism on the first day, increases it noticeably on the second, and produces a very pronounced increase on the third.