CHAPTER XL 



DIETETICS 



BRIEFLY stated, we take in food 



1. To rebuild the living tissues. 



2. To obtain energy for the biological processes. 



3. To preserve the proper medium in which these pro- 



cesses can be carried out. 



The Selection of Foodstuffs. Hitherto we have spoken of proteins,, 

 fats, and carbohydrates, somewhat as if they were usually found 

 separately, as such, in the food materials in common use. This is not 

 the case in regard to the majority of the commoner natural food 

 materials. These are mixtures of all three classes of nutrients, as. 

 can be seen from the following tables. Nevertheless, the food materials 

 can be grouped, according to their constitution, into those which are 

 mostly protein, mostly fat, mostly carbohydrate, or mostly water. 

 Some prepared foodstuffs, such as sugars and starches, or butter and 

 oils, are almost exclusively one class. 



Iii regard to practical dietetics, several important points have to- 

 be considered: 



1. The amount and proportion of the various foods which are neces- 

 sary to meet the physiological needs of the body at different ages in the 

 different sexes, and under various conditions of activity and environment. 



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