CHAPTER IV 

 A STUDY OF FOODS 



Why Foods are needed in the Body. In our study of the 

 composition of the body (pp. 16-19) we discussed the pres- 

 ence of water, proteids, fats, carbohydrates, and mineral 

 matters. We have learned, also, that in the presence of 

 oxygen some of these materials are oxidized, thus forming 

 the waste substances carbon dioxid, water, and urea. Hence, 

 if the body is to continue its activities, there must be a con- 

 stant supply of new material. This supply we obtain in our 

 foods. 



Definition of a Food. The three most important uses of 

 foods were suggested on p. 30 in the preceding chapter. 

 Hence we may say a food is any substance that yields material 

 for the repair or growth of the body, or that supplies the fuel 

 used by the body for producing heat or poiver to do work. 



1. THE COMPOSITION OF FOODS 



Nutrients. Our common foods are made up of many 

 different compounds. Bread, for example, is composed of 

 water, salt, starch, sugar, fats, and proteids. Over 80% of 

 butter is fat; the other 20% is largely water and salt. 

 These ingredients of food that can be used by the body are called 

 nutrients. They may be classified as follows : (1) proteids 

 (known also as albuminous and nitrogenous foods), (2) fats 

 (and oils), (3) carbohydrates (starches and sugars), (4) min- 

 eral matters, and (5) water. 1 



1 By some writers water is not regarded as a nutrient. Since, how- 

 ever, it is an essential constituent of protoplasm, it may well be named 

 among the nutrients. 



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