DIGESTIBILITY AND AVAILABILITY OF FOOD. I 79 



ON THE DIGESTIBILITY AND AVAILABILITY OF 

 FOOD MATERIALS. 



BY W. O. ATWATER. 



As stated in previous reports, the Station has for .several 

 years cooperated with the U. S. Department of Agriculture in 

 experimental inquiries upon the food and nutrition of man. 

 These inquiries have included analyses of food materials, de- 

 terminations of their heats of combustion and fuel values, 

 dietary studies in which observations were made of the kinds 

 and amounts of food consumed by people of different classes, 

 experiments on the amounts of the nutrients of food digested 

 and made available to the bod}^ and finally, so-called metabol- 

 ism experiments, the purpose of which is the study of some of 

 the fundamental laws of nutrition. A large number of these 

 latter experiments have been made with the respiration calo- 

 rimeter which was described in the Report of the Station for 

 1897. I^h^ object of these experiments is to study the income 

 and outgo of material and energy in the human body and thus 

 obtain information regarding the ways in which the body uses 

 its food, the values of different food materials for nourishment, 

 and the kinds and amounts fatted to the demands of people of 

 different classes and under different conditions. 



One important factor of the nutritive value of a given food 

 is its digestibility. The word digestibility in popular parlance 

 has a by no means definite signification. As used by the 

 phj'siologist it applies to the chemical changes which the food 

 undergoes in the alimentary canal in order to fit it for absorp- 

 tion and consequent utilization by the body. The particular 

 feature of the digestibility of food in this .sense is found in the , 

 quantities of the several nutrients which are thus digested, ab- 

 sorbed and niade available to the body. The purpose of the 

 present article is to give the results of a considerable number 

 of digestion experiments in their bearing upon this especial sub- 

 ject, namely, the proportions of the nutrients of food materials 



