NUTEITION 235 



D. THE PROPER DAILY INTAKE OF PROTEIN 



21. The economic and the physiological question. The 

 proper amount of protein in the diet is both economically 

 and physiologically important. Since foods rich in protein 

 meats, eggs, dairy products, etc. are among the more ex- 

 pensive foods, it is often for a family with limited income 

 a practical question how much of these foods must be used 

 to assure proper nourishment of the body. In this work we 

 are more directly concerned with the physiological effects of 

 low, moderate, and abundant protein diet, but the answer 

 to this question also gives the answer to the economic ques- 

 tion, since the problem in the latter case is to keep down 

 the consumption of the more expensive foods to the level 

 which is consistent with adequate nutrition. 



It is comparatively easy to determine whether the fuel 

 value of the diet is adequate. If it is insufficient, loss of 

 weight inevitably results ; if it is excessive, and especially 

 if it is excessive in fat and carbohydrate, there is apt to be 

 increase of weight. An equilibrium of total intake and out- 

 put for months usually indicates that the fuel needs of the 

 body are being met. Equality of intake and output of pro- 

 tein, on the other hand, does not prove that the protein of 

 the diet is what it should be, for the body breaks down all 

 the protein it consumes whether the amount be excessive or 

 not. We can, however, determine by dietary studies what 

 is the usual consumption of protein by different classes of 

 people and also what is the lowest intake upon which 

 protein equilibrium may be maintained in the body. 



22. The usual and the minimum intake of protein. When 

 the choice of food is not restricted by economic or other 

 consideration, but is determined solely by appetite or the 

 feeding customs of one's home or community, the protein 

 intake of an adult healthy man usually varies between 100 

 and 150 grams daily. This is equivalent to from 500 to 



