53 



nutrients of a mixed diet actually utilized by the bodj' under the 

 experimental conditions previously noted. As may be seen from 

 the figures summarized above, the results for the different subjects 

 were for the most part quite uniform, the range in percentages of 

 digestibilit.y of the different nutrients being from 82.9 to 87.0 for pro- 

 tein, 9(;.7 to 98.3 for fat, and 0().7 to 08.5 for carbohydrates, while the 

 availability of energy ranged from 91.8 to 93 per cent. The average 

 of the results for all six subjects, i. e., protein 85.3 per cent, fat 07.4 

 per cent, carbohydrates 98 per cent, and energy 92.0 per cent, there- 

 fore, gives a fair indication of the digestibility of the nutrients and 

 availability of the energy of the diet under the conditions of these 

 experiments. 



On the basis of a large amount of data obtained in upward of 400 

 digestion experiments made in connection with the nutrition investi- 

 gations of this Office, of which those here reported form a part, it has 

 been estimated that on the average about 92 per cent of the protein, 

 95 per cent of the fat, 97 per cent of the carbohydrates, and 91 per 

 cent of the energy of ordinary mixed diet is digested and made avail- 

 able to the body. It will be noticed that except in the case of the 

 protein there is a fairly close agreement between these factors and 

 the average of the results of the digestion experiments summarized 

 above. The discrej)ancy in the case of the protein may doubtless be 

 accounted for by differences in the proportion of animal and vegeta- 

 ble protein in the diet. That is, in the diet of the present experi- 

 ments, as shown by the figures in Table 28 bej^ond, about 60 per cent 

 of the total protein on the average was derived from vegetable food 

 and only 40 per cent from animal food, whereas in the experiments 

 upon which the above-mentioned factors were based the average pro- 

 portion of protein from animal foods was more nearly 60 per cent 

 and that from vegetable foods 40 per cent. Since the digestibility of 

 vegetable protein is lower than that of animal food, obviously the 

 digestibilit}'^ of total protein would be lower in the diet in which vege- 

 table protein predominates, as in the present case. 



If these facts be taken into consideration it would appear that the 

 men in these experiments digested the protein of their diet, as well as 

 the other nutrients, in very nearly the proportions that have been 

 found for the average individual on ordinary mixed diet. This may 

 be illustrated by a comparison between the results actually determined 

 in the experiments and those calculated from the data of food eaten 

 by use of factors representing the average digestibility of the nutrients 

 in different classes of food materials. Such factors, deduced mainly 

 from the results of the large number of digestion experiments referred 

 to above, are here given. ^' 



« Connecticut Storrs Station Rpt. 1899, p. 86. 



