FOOD REQUIREMENTS 



99 



afford to live exclusively on proteins when fats and carbohy- 

 drates are available ; and it is really worth while to reduce the 

 protein in the food to the lowest proportion of practical safety ; 

 that is, to find the nutritive ratio that serves our practical 

 purpose. From a consideration of the dietary standards of 

 Voit, Atwater, Chittenden, and other investigators (see p. 93) 

 we can see that, whichever standard is adopted, the protein 

 ratio falls within certain definite limits. This is clearly shown 

 by the comparison given in the following table : 



A protein ratio of from I .-7.5 to 1:9 is a good average, 

 although a smaller person or a person doing a large amount of 

 muscular work would need a lower protein ratio. 



If we calculate the number of calories and the amount of 

 protein in our supposed breakfast, by using either the Fisher 

 table or the Rexford table, we shall find that the total food 

 represents from 620 to 750 calories, with a protein ratio of 

 from i : 6 to 1:7, according to the size of egg or banana 

 and the size of bread slices assumed. 



136. Standard diets. To make practical use of the idea of 

 standard diet we have further to consider (i) the age of a 

 person, (2) the amount and character of his day's work, and 

 (3) the seasons of the year. 



The age is important because (i) the digestive system of 

 young people may not be able to tolerate what an older person 

 can stand ; (2) a young person is usually smaller and so uses 

 up less proteins each day ; and (3) a young person is growing, 

 and so uses more proteins for building new tissues than an 

 older person does. 



