THE PLACE OF PKOTEINS IN THE DIET IN THE LIGHT 

 OF THE NEWEK KNOWLEDGE OF NUTRITION 1 



H. H. Mitchell, Ph. D. 

 Associate professor of animal nutrition, University of Illinois 



The functions of food in the animal body include, first, the fur- 

 nishing of fuel for conversion into the various forms of energy that 

 characterize living matter, and, second, the furnishing of material 

 for the growth and* upkeep of the body itself. From the fact that 

 the solid matter of the active tissues of the body is so largely com- 

 posed of protein, it is obvious that dietary protein is of the utmost 

 importance in serving this second function of food. 



In the utilization of food protein by animals, just as in the utiliza- 

 tion of food energy, a certain wastage of material seems to be in- 

 evitable. The first wastage is due to incomplete digestibility. There 

 is a marked difference in the digestibility of the proteins of different 

 foods. The animal proteins in particular seem to be completely 

 digested, or very nearly so, when not dried or overcooked, the white 

 of egg constituting an exception to this statement. The proteins of 

 cereals, vegetables, and fruits occupy an intermediate position, being 

 only about 85 per cent digestible. Egg albumin is also of about this 

 digestibility. The proteins of the legumes possess digestion coeffi- 

 cients of 80 or less. 



However, these differences in the digestibility of proteins do not in 

 the main depend upon chemical differences existing between them, 

 but rather upon the presence in the food of indigestible carbohyd- 

 rates, such as celluloses, hemicelluloses, and pentosans. Mendel and 

 Fine have shown 2 (1) some years ago that these differences largely 

 disappear when the vegetable proteins are fed in a more nearly pure 

 condition. They found that the proteins of wheat were as well uti- 

 lized as the proteins of meat, and that the proteins of barley and of 

 corn were also probably as well digested. With regard to the pro- 

 teins of soy beans, navy beans, and peas, they concluded that the 

 presence of indigestible nonnitrogenous materials can not entirely 



1 Read before the Food and Drugs Section of the American Public Health Association at 

 the fifty-first annual meeting, Cleveland, Oct. 17, 1922. Reprinted by permission from the 

 American Journal of Public Health, January, 1923. 



2 References are to notes at end of paper. 



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