496 SYMPOSIUM ON FOOD PROBLEMS 



ing the protein requirements, either of maintenance or of growth, 

 when it is supplemented by even a small amount of milk protein. 



That the supplementing of the grain protein by milk is of greater 

 importance during growth than in the mere maintenance of a full- 

 grown person is fairly obvious from the fact that in the latter case 

 it is only necessary to maintain an already established equilibrium 

 between tissue protein and amino acids. Any of the amino acids 

 whose radicals are contained in tissue proteins may be expected to 

 function in such maintenance, whereas there can be no growth 

 unless all the amino acids represented in tissue proteins and not 

 formed in the body are present in suffiicent abundance. 



Even in the case of the full-grown organism persistent use of a 

 diet consisting too exclusively of grain products, or seeds of any 

 kind, may lead to unfavorable results, but this is true of wheat as 

 well as corn and is no objection to the substitution of the one for 

 the other. 



Such substitution of corn (and presumably of other grains) for 

 wheat will leave practically unchanged the nutritional efifiiciency of 

 the diet and the usual margin of safety above actual requirements 

 which is characteristic of the average American food supply. 



What then is this margin in the case of the different factors of 

 food value and how will it be affected by the other substitutions 

 which the present food situation demands ? 



In view of the findings just presented by Dr. Benedict and the 

 fact that in most food studies outside of the laboratory it is not 

 practicable to make accurate record of the muscular activities of the 

 persons concerned, any attempt to estimate the percentage by which 

 the total food intake of the average American family exceeds its 

 actual food requirement as expressed in calories, would necessarily 

 involve several assumptions the discussion of which would extend 

 the present paper beyond its assigned limits. 



In the study of protein requirement the assumptions are fewer 

 because muscular activity is here not an appreciable factor, but the 

 data of different investigations are less concordant than in the study 

 of energy metabolism. The results of a review of the literature of 

 protein requirement up to 1917 with an attempt to select the experi- 

 mental data which are comparable with each other and applicable 



