214 Metabolism of Healthy Man. 



During waking hours. With the necessarily greater unrest of subjects sitting 

 in a chair, discrepancies in the determination of oxygen, which would ultimately 

 vitiate to a certain extent the determination of the respiratory quotient, are 

 frequently found. Many of the respiratory quotients, however, were determined 

 with considerable accuracy and the results are reported in table 89. The vari- 

 ations are fully as great as in sleep and the table serves admirably to show that 

 there may be wide variations in the respiratory quotient, not only between dif- 

 ferent individuals, but also with the same individual on different days. The 

 average of all the experiments showed a respiratory quotient of 0.87. Since 

 many of these experiments were made during the day and when full digestion 

 was in process, it is fair to assume that the result indicates the average respi- 

 ratory quotient daring waking hours of the average man. This average value 

 is considerably less than that commonly reported in text books, namely, 0.93. 

 As has been pointed out frequently, however, the respiratory exchange is 

 dependent in large part upon the character of the diet. If a diet containing a 

 large quantity of carbohydrate is ingested, the respiratory quotient is high; if 

 the diet contains a large amount of fat and is relatively low in carbohydrate, 

 the respiratory quotient is low. Aside from indicating the general nature of 

 the diet partaken of by man, the respiratory quotient as determined in experi- 

 ments of this type has little, if any, value. 



During period without food. While the respiratory quotient extending over 

 a 24-hour period has little or no value, owing to the varied nature of the diet 

 partaken of by different individuals, the respiratory quotient determined 12 

 hours after the last meal has been used by many investigators as the base line 

 for an extended series of investigations. It is thus assumed that 12 hours after 

 the last meal when the stomach is empty and the effect of the previous diet is 

 practically past, the subject is then living upon the protein, fat and carbohydrate 

 of the body. The relative amounts of the materials oxidized depend in large 

 part upon the previous storage of carbohydrate, chiefly glycogen of the body, 

 and this is assumed to be a relatively constant amount for given individuals. 

 The experiments here presented throw some light upon this subject and in table 

 90 the respiratory quotients have been computed, first, for the period from 

 1 a. m. to 7 a. m., and second, for a subsequent period at least 12 hours after 

 the last meal is taken at 6 p. m. the night before. Theoretically one would 

 expect to find almost invariably a noticeable diminution of the respiratory quo- 

 tient as time progresses. This is clearly shown in 24-hour experiments with 

 fasting man. 1 On the first day there is a heavy draft upon the body glycogen 

 and the respiratory quotient is relatively high. On the second day, when the 

 body glycogen has been considerably drawn upon so that the metabolism becomes 

 chiefly that of fat, the respiratory quotient falls to not far from 0.74. In the 

 experiments in table 90, the preliminary period shows, as a rule, a somewhat 



Benedict, Carnegie Institution of Washington Publication No. 77, 1907, p. 451. 



