292 ANT^UAL REPORT SMITHSONIAN INSTITUTION, 19 42 



of calories to the point that sufficient food is not consumed to sup- 

 ply the normal vitamin requirement. We still speak of the protein 

 requirement in total grams of protein in the diet, while actually it 

 is not the protein requirement that we are interested in, but the 

 amino acid requirement. Some day we may be able to state the 

 actual amino acid requirements and obtain values for the amino acid 

 content of all our food supplies. At present this may seem very 

 difficult, but the analysis of food materials for vitamins A, B,. and 

 C also appeared very difficult a few years ago. The value of 70 

 grams of protein per day for an adult man is probably a safe figure 

 provided we specify that the protein should be derived from a va- 

 riety of sources and a good part of it from animal tissues. 



No definite figures have been established for the fat content of 

 human dietaries. It is generally concluded that fat must be a con- 

 stituent of the normal diet and that it is well to use liberal amounts 

 to supply the fat-soluble vitamins. The latter suggestion is not 

 absolutely essential since we can now get concentrates of these vita- 

 mins; however, the importance of fat as a source of linoleic acid 

 must be considered. There is no question about the production of 

 linoleic acid deficiency in rats on fat-low diets but few studies have 

 been made with other species. There is some difference of opinion 

 concerning the importance of linoleic acid in the human dietary. A 

 high intake of linoleic acid containing fats has been used in the 

 treatment of eczema; and Brown, Hansen, Burr, and McQuarrie (2) 

 found a decrease in the amount of linoleic acid and arachidonic acid 

 in the serum of an adult man subsisting for 6 months on a diet ex- 

 tremely low in fat. The individual exhibited no other evidence of 

 disease. We have found in our laboratory that rats maintained on 

 mineralized skim milk fortified with minerals and the fat-soluble 

 vitamins grow better when the skim milk is supplemented with butter 

 fat than when vegetable oils are used. The active substance is pres- 

 ent in the fatty acid fraction of the butter fat. 



It is also well known that fat has a sparing effect on vitamin Bi. 

 The general decrease in the fat content of American dietaries has 

 thus tended to aggravate the vitamin Bi deficiency brought about by 

 the use of refined foods. 



Calcium logically heads the list of mineral elements of significance 

 in nutrition since there is more calcium in the human body than any 

 other mineral element. The value generally accepted today as an 

 adequate level is 0.7 to 0.8 gm. per day. We must first recognize 

 that this calcium requirement holds only when the diet contains 

 an adequate supply of vitamin D. The Ca : P ratio is also a factor 

 that needs definite consideration. We still find in certain textbooks 

 that the optimum Ca : P ratio is 2:1. This is obviously incorrect 

 since in all of our work we have found the ratio to approach 1.2 : 1. 



