Again, the 24-hour period gives no information as to the time relations or the maximum effect following the ingestion of food. We are thus unable to tell from the results whether the increase extends over a long period or whether there is a sharp rise and fall in metabolism, i. e., a "peak" effect. Nor does it take into consideration the remote possibility of a compensation - that is, a subsequent lowering of metabolism. The evidence as a rule indicates an increment in metabolism, but certain experiments, as we have seen in the summary of the literature on this subject (see page 40), have at least suggested a depression of the basal metabolism.

Furthermore, with the 24-hour period it is practically impossible to detect slight increases, which may actually occur but be lost in the daily quota. These increases could be demonstrated if the maximum effect could be obtained by means of measurements in short periods immediately following the ingestion of food. In a study on the influence of food upon metabolism it would therefore be expected that the 24-hour type of experiment could be satisfactorily used only when studying classes of foods which produce a considerable increment in metabolism rather than for securing evidence regarding foods which cause but a slight increase in metabolism.

Discussion Of Results Of Fasting And Food Experiments On The 24-Hour Basis

In view of the results obtained in the fasting studies carried out at Wesleyan University and later in the Nutrition Laboratory, the selection of a suitable basal value to be used for the 24-hour food experiments has been a subject of much consideration. As will be shown later, in our discussion of the experiments and in our conclusions as to the use of this type of experiment, the length of the fast influences the increment in the metabolism due to the ingestion of food. In discussing the basal metabolism in this special group of 24-hour experiments, therefore, it has seemed desirable to give the detailed results obtained after the taking of food, presenting only those fasting values which have been selected for the base-line. The data for the food experiments, when significant, will later be included in abstract in several tabular presentations of final results and in the discussion of special food topics. They are presented here primarily as material for a critical study of the general principle of the use of 24-hour periods. In giving the data for these experiments, the fuel value of the diet, i. e., the heat of combustion less the unoxidized portion of the protein excreted in the urine, has been used in all cases. For the method employed in calculating these values, see page 334.

The first series of experiments on the 24-hour basis is that for A. L. L., December 16 to 23, 1904.1 In this series 4 fasting days preceded the ingestion of milk and plasmon. In table 7 the average of the first 2 days is used as a base-line, these values being the best available for comparison, as will be shown later (see page 70). The average excretion of nitrogen for the first 2 days of fast was 12.18 grams, the carbon-dioxide production 649 grams, the oxygen consumption 615 grams, and lFor the detailed results of this series see Benedict. Carnegie Inst. Wash. Pub. No. 77. 1907, experiments Nos. 69 and 70 the heat production 2,057 calories. An examination of the values for the fourth day of fast, December 19 to 20, shows that they are somewhat lower than the basal values obtained from an average of the first 2 days. On all of the 3 food days there was a gradual increase in the carbon-dioxide excretion, oxygen consumption, and heat production as a result of the ingestion of the milk and plasmon, the largest amount being on the last day. Thus, on the 3 days with food there were successive increases of 4, 37, and 128 grams in the carbon-dioxide production, 7, 56, and 118 grams in the oxygen consumption, and 47, 166, and 400 calories in the heat production.

Table 7. - A. L. L., December 16-23, 1904. (24-Hour Periods, 7 A. M. To 7 A. M.) Milk And Plasmon1

Amount, 1,621 grams; nitrogen, 8.57 grams; total energy, 2,577 calories. Fuel value, 2,502 calories; from protein, 9 per cent; from fat, 79 per cent; from carbohydrates, 12 per cent.

1Expressed as average per day, since the amounts and nutrients were essentially the same each day.

With this particular experiment, in which an increment was noted on all 3 days with food, the discussion of the results is comparatively simple. Judging by this experiment alone, it is clear that the ingestion of food increased the metabolism over that of the fourth day of fasting, thus bringing the values for the first food day positively above the average for the first 2 days of fasting; there was also a cumulative effect, for although exactly the same amount of food was given each day and there was apparently the same amount of muscular activity, the metabolism distinctly increased each day. This increase amounted on the first day to but 2 per cent of the fuel value of the intake, on the second day to 7 per cent, and on the third day to 16 per cent. As only a small amount of plasmon was taken and the milk used was a modified milk and contained considerable fat, the actual amount of nitrogen ingested was not large; hence the increment due to the stimulating action of protein could not be expected to be very great. In addition, it should be pointed out that 79 per cent of the energy came from milk fat. Obviously if the last day of fasting were taken as the base-line, all of the increments would be materially larger.