11 



Foods ana Nutrition 



Nature of Nutrition 



Nutrition is a remarkable process by which the protoplasm of a cabbage 

 becomes rabbit, that of a fish becomes cat, and the proteins of lamb are trans- 

 formed into proteins of man. The processes of nutrition include: the physical 

 and chemical breakup of foods called digestion; the absorption by cells of the 

 foods simplified by digestion; and assimilation, by which the basic units of pro- 

 tein are interwoven into the particular pattern of proteins of the animal nour- 

 ished, and the simplified carbohydrates and fats stored to be available for 

 energy. All cells of the body and the chromosomes within them are nourished 

 in this way. Human chromosomes doubtless contain substances that originated 

 in beans and cattle, but they have lost their original characteristics and by 

 assimilation have become the protein peculiar to the chromosomes of man. 



Nature of Foods 



Foods are the substances that are taken into the body and used in its metab- 

 olism, in building protoplasm for growth and repair, and in liberating energy 

 to do work. Work includes all activity such as movement, responses of the 

 sense organs, and secretion of glands. Animal food consists of plants and ani- 

 mals and their products, such as sugar and milk. The essential substances are 

 proteins, carbohydrates, fats, vitamins, and very small amounts of certain 

 minerals (Fig. 11.1). Water, necessary for all organisms, is essential in the 

 process of nutrition. 



Proteins. Since protein is constantly being broken down in the body, more 

 of it must be furnished for repair as well as for growth. When there is no pro- 

 tein in the food, the body burns its own protein. This happens in starvation. 

 Sixteen per cent of protein is nitrogen. The body must be kept in a nitrogen 

 balance, that is, as much nitrogen should be taken in as is excreted, and some- 

 times more, as during pregnancy, during growth, and after injury or illness. 

 Proteins are abundant in meat (muscle), cheese, eggs, peas, and beans. Their 



168 



