In the first experiment with S. A. B., the ingestion of food, with a fuel value essentially that of maintenance during fasting, resulted in a slight increase in the metabolism on the first food day over the metabolism on the fourth fasting day. If, however, the average of the fasting days is taken as an absolute value, it will be seen that the ingestion of food simply checked the progressive decrease in the metabolism. Here again the uncertainty of the base-line is noticeable.

In the second experiment with S. A. B., the ingestion of food with a fuel value considerably above the 24-hour maintenance requirement (over 500 calories above the final fasting-level) resulted in an increase in heat production of a little over 100 calories, while in the last experiment with S. A. B. the ingestion of food with a fuel value about 200 calories higher than the heat production on the sixth and seventh fasting days resulted in an increase in the metabolism of approximately 200 calories, the daily metabolism on the food days being almost exactly equal to the fuel value of the intake.2

From this varied picture of the influence of food ingestion upon metabolism following fasting, certain rather clear conclusions may be drawn. First, in all instances food produced an increased metabolism over the last fasting day. This increase was independent of whether the fuel value of the food was considerably above or below that required for maintenance on the fasting day. Second, with the same individual the reaction to food was apparently by no means constant, for in the first two experiments with S. A. B. there was little, if any, increment due to food, although in the second experiment the fuel value of the food was from 400 to 500 calories above fasting maintenance requirements. On the contrary, at the end of the 7-day fast, food with a fuel value of 200 calories greater than the heat production of the last fasting day produced an increase of 200 calories in the total heat production. In all probability the length of the fast, the influence upon the basal metabolism of the fasting per se, the fuel value of the intake, and the proportion of protein in the intake are in some way related. In all of the experiments reported in this table there was an actual loss of nitrogen during the food experiment, as there was not sufficient protein in the intake to compensate for the outgo.

1Benedict, Carnegie Inst. Wash. Pub. No. 203, 1915, p. 372.

2Grafe (Deutsch. Arch. f. klin. Med., 1913-14, 113, p. 1), comparing results obtained in a prolonged fast with those obtained with a diet of almost pure carbohydrates, found no rise in the metabolism after food.

Finally, although the evidence is somewhat meager, it is of fundamental importance to consider the relationship between the ingestion of food and the basal metabolism after fasting, with a view to considering the possibilities of lowering the basal metabolism by inanition or undernutrition, and then maintaining the metabolic level on smaller food requirements than those ordinarily obtaining. For example, in the first experiment with S. A. B., we have a heat production on the second fasting day of 1,844 calories. On the fourth day this was reduced to 1,606 calories. The fuel value of the food ingested was 1,698 calories, which was essentially that required for maintenance. It is quite clear, therefore, that we deal here with a maintenance, at least temporarily obtaining, at a level of 150 or more calories below that on the second fasting day. The fact that in the second experiment with S. A. B. the 2,078 calories in the food did not cause a pronounced rise in the metabolism is likewise of great significance, for by 5 days of fasting the basal metabolism was lowered over 300 calories, and the ingestion of an excess amount of food over requirements on the next 3 days increased the heat production only about 100 calories above the last fasting day. On the other hand, these conclusions are considerably weakened by the course of the metabolism in the last experiment with S. A. B., in which food with a fuel value a little above the fasting requirements produced an increment of 200 calories, raising the metabolism to that on the first three or four fasting days.

These experiments are extremely suggestive in their bearing on the question of a basal metabolism lowered either by fasting or by prolonged undernutrition. They should be followed by observations on the influence of very moderate or barely maintenance diets to note if the tendency of the basal metabolism is to return to the initial value or to maintain the lowered value found as a result of undernutrition or inanition. The reported experience of Germany and Austria at the time of writing would seem to indicate that observations of this kind are unwittingly being made there, but unfortunately it is probable that these are without a scientific measurement of the basal metabolism.1 The statistical and superficial evidence indicates that certain classes of the Teutonic nations are subsisting on very low diets, so far as the calorie intake is concerned. While definite information is lacking as to their capacity to perform physical work on this low diet, the evidence of scientists who have visited Europe is somewhat conclusive in leading to the belief that there has been no proportionate loss in physical prowess or ability to perform work by this reduction in basal requirements. It is evident that this should be made the subject of most careful physiological research,2 as apparently during fasting the organism becomes accustomed to existing upon a perceptibly lower level. There is naturally a loss of weight which is, it is true, in some small part made up of organized protoplasmic tissue and in large part of water and fatty tissue, but it is hardly conceivable that the heat-producing organism as such is proportionately reduced in capacity or size by the fasting. It is probable, however, that the stimulus to cellular activity is considerably lowered as a specific result of the fasting process. To what extent this stimulus is regenerated by moderate amounts of food, and how much the total metabolism may be influenced by the introduction of foreign protein, even under conditions when there is a draft upon body protein, are at present unsolved problems which should be carefully studied.

1Since writing the above we have been able to secure a copy of an article by Loewy and Zuntz (Berlin, klin. Wochenschr., 1916, 53, p. 825) and find that studies of the basal metabolism of both authors have been made with all the accuracy and painstaking care characteristic of Professor Zuntz's work. A pronounced decrease in basal metabolism as a result of the enforced reduction in diet is noted in both cases.

2Such a research has but recently (February 3, 1918) been completed by the Nutrition Laboratory and the data are now being elaborated for publication.