COMPOSITION OF FOODS 305 



carbohydrate column is mostly starch, except in milk, 

 where it is all sugar. 



The amount of energy yielded when a pound of food 

 is oxidized is expressed in calories. For example, 

 one pound of butter will yield 3405 calories of heat 

 and one pound of strawberries only 175 calories. The ash 

 content represents the mineral salts present. 



According to this table, which foods will yield the 

 most protein ? Carbohydrate ? Fat ? Energy ? 



Use of foodstuffs. As we have stated before, food is 

 used for the repair and growth of the body and to 

 supply energy in the form of heat or action. Energy 

 is the ability to do work. Both action and heat are 

 thus forms of energy. Foods must supply the body 

 with building material and with fuel. 



Building material. Some foods, the nitrogenous 

 ones, supply all that is essential for the growth and 

 repair of the body. We would expect this when we 

 recall that the body is composed of cells, that cells 

 contain protoplasm, and that protoplasm and protein 

 are nearly identical in composition. Mineral salts are 

 known, too, to share in this repair. Proteins may be 

 oxidized, but this is not their principal use. 



Fuel. It may be that carbohydrates and fats are 

 used as building materials, but their principal use is to 

 serve as fuel. When they are oxidized they supply heat 

 and power. Fat is especially suited to this purpose; 

 that is the reason why inhabitants of cold coun- 

 tries eat such large quantities of fatty foods. Some 



