The results of the food experiment with A. H. M., February 2 to 3, 1906, are given in table 22, together with the average values for the fasting experiment of November 21 to 23,1905. The values obtained on the two fasting days agree closely; the average heat production was 1,755 calories. With the ingestion of the crackers and milk, which had a total fuel value of about two-thirds of the daily requirement, the heat production was increased 239 calories, with a corresponding increase in the carbon-dioxide production and oxygen consumption. Here again it is extremely difficult to account for the unusually large increment. While it would normally be ascribed solely to the ingestion of the food, it is so at variance with the results obtained in almost all of the other experiments that one must question the reliability of the base-line. This experiment is an admirable illustration of the unsatisfactory use of 24-hour periods, particularly when there is a considerable interval of time between the determination of the basal value and that determined after the ingestion of food.

Table 22. - A. H. M., February 2-3, 1906. (24-Hour Periods, 7 A. M. To 7 A. M.) Crackers And Milk1

Amount, 1,150 grams; nitrogen, 7.34 grams; total energy, 1,314 calories. Fuel value: Total, 1,250 calories; from protein, 15 per cent; from fat, 39 per cent; from carbohydrates, 46 per cent.

1The food was eaten mostly in three portions, at 9 a. m., 1 p. m., and 6 p. m. Soda crackers and graham crackers were used with the milk. 2For period 6h45m a. m. Feb. 2 to 7 a. m. Feb. 3.

General Conclusions Regarding Use Of 24-Hour Periods

From the foregoing discussion of the results of the experiments made on the 24-hour basis, it is seen that serious objections may properly be raised to this type of experiment, even though on first consideration the method may seem theoretically desirable. Experience with fasting men, both at Wesleyan University and in the Nutrition Laboratory,1 has demonstrated that the metabolism progressively decreases as the fast continues. In the fast studied at the Nutrition Laboratory, in which accurate graphic records of the activity were obtained, this decrease in the fasting metabolism occurred with considerable uniformity at least 31 days, accompanied by a proportional loss in body-weight. In view of the steady loss in weight, it seems illogical to use values for a base-line which were determined under such conditions, particularly if the values are not compared on the basis of per kilogram of body-weight or per square meter of body-surface.

Furthermore, the depression in the metabolism due to fasting is abnormal, for evidently we have here a process entirely distinct from that due to the mere absence of food in the digestive tract. If we are to follow the contention of Johansson, we must consider the digestion of food and the daily body metabolism as two entirely independent processes, the body drawing continually upon its several depots for its immediate needs and the ingestion of food resulting in a separate process for replenishing these depots. At the time our studies of the basal metabolism begin (approximately 12 hours after the ingestion of food), active digestion has ordinarily ceased and the body deposits are presumably still in a normal condition, with the usual liberal supplies of glycogen, fat, and protein. During the post-absorptive condition the body begins to draw upon these deposits, particularly the glycogen, and in approximately 2 to 4 days of fasting the labile glycogen supply is heavily depleted; thereafter the metabolism remains essentially a protein-fat katabolism until food is again taken. As a result of these heavy drafts upon body material during fasting, we have, after one or two days of fast, a condition which represents at least the beginning of inanition. It would appear, therefore, that as soon as the general nutritive condition of the body is seriously affected by a disturbance in the proportion of body materials, we pass outside the field of measurement of the basal metabolism for studies on the influence of food. It is well known that one of the first effects of the ingestion of food after long inanition is the replenishment of the reserves of body material, and there is excellent evidence that this replenishment is accomplished by processes materially different from those occurring during ordinary digestion.

1Benedict, Carnegie Inst. Wash. Pub. No. 77, 1907, and No. 203, 1915.

For the majority of experiments in which the effect of food is studied, a sharp differentiation between the post-absorptive condition and the beginning of inanition is unnecessary, but in certain of our experiments, especially those made in 24-hour periods, when the ingestion of food was 24, 36, 48, or even 60 and more hours after the last meal, we may have a condition of the body which distinctly approximates the first stages of inanition. The increment due to the ingestion of food would therefore be based upon abnormal values which would theoretically be somewhat lower than those ordinarily used for such studies. With so low a basal value, it frequently occurs that the stimulus of food simply compensates for the depressing influence of the previous fast and no increment in the metabolism is found. The effect obtained from the ingestion of food thus becomes a function of the duration of the fasting. For this reason the series of experiments in which the period of fasting was limited to two days are logically more satisfactory than those in which the subject fasted for a longer period.

The greatest practical difficulty encountered in the use of the 24-hour method of experimenting was the fact that after one or two days of fasting the subjects were frequently unable to eat appreciable quantities of food without distress. In the series of 2-day fasting experiments with college students at Wesleyan University, the experimental plan included the ingestion of unusually large amounts of food on the third day for the purpose of obtaining maximum effects. To our surprise and disappointment, it was found in many cases that the subjects could not eat large amounts of the food, or, having eaten it, they experienced distress, this being particularly true when large quantities of a single food or pure food substance were given. Accordingly, the most of our experiments were made with relatively small amounts of food, with a correspondingly small fuel value, this fuel value occasionally representing but one-half or two-thirds of the daily needs. It was only when the period was somewhat curtailed and the observations confined to the night period that satisfactory base-lines could be obtained and the effect of the superimposed food definitely determined without the disturbing factor of the depression due to fasting. This latter plan of experimentation leads us naturally into the subdivision of the experimental day and a complete abandonment of the 24-hour method of experimenting.

From the foregoing considerations the only conclusion that can be reached is that the 24-hour period does not lend itself to a sharply defined study of the influence upon metabolism of the ingestion of food - first, because the establishment of a suitable basal value is extremely difficult, since each day of fasting shows a lowered metabolism as the specific result of the fasting; and second, because it has been proved physiologically impossible for many subjects, after two days of fasting, to take large amounts of food. These large amounts are particularly desirable for studying the influence upon the metabolism of a special food substance, especially as the increment, which is frequently slight, must be included in the total measurements for the 24-hour period and would thus in some cases, either wholly or in part, escape observation. This plan of experimentation thus defeats its own end, minimizing the effect of the food ingestion by a physiological reaction of the subject after fasting, and attenuating the frequently small increment in the metabolism due to the stimulating action of the food materials.