70 FOOD 



engine, the energy of the coal is used to run the engine, but if 

 the engine were like the human body, one third of the ton 

 would be used in keeping walls, shafts, wheels, and belts of the 

 engine in order, and only two thirds would go toward running 

 the engine. 



When an engine is not working, fuel is not consumed, but the 

 body requires food for mere existence, regardless of whether it 

 does active work or not. When we work, the cells break down 

 more quickly, and the need for repair is greater than when we 

 are at rest, and hence there is need of a larger amount of food. 

 But whether we work or not, food is necessary ! 



The different foods. The body is very exacting in its 

 demands, requiring certain definite foods for the formation 

 and maintenance of its cells, and other foods, equally definite, 

 but of different character, for heat and energy. Our diet there- 

 fore must contain foods of high fuel value, and foods of cell- 

 forming power. 



Although the foods which we eat are of widely different 

 character, such as fruits, vegetables, cereals, oils, meats, eggs, 

 milk, cheese, etc., they can be put into three great classes: 

 carbohydrates, fats, and proteins. 



The carbohydrates. Corn, wheat, rye, in fact all cereals 

 and grains, potatoes, and most vegetables are rich in carbo- 

 hydrates, as are also sugar, molasses, honey, and maple sirup. 

 The foods of the first group are valuable because of the starch 

 they contain; for example, corn starch, wheat starch, potato 

 starch. The substances of the second group are valuable be- 

 ^ause of the sugar they contain. In the sirups there is a con- 

 siderable quantity of sugar, while in some fruits it is present in 

 more or less dilute form. Sweet peaches, apples, grapes con- 

 tain a moderate amount of sugar; watermelons, pears, etc., 

 contain less. Most of our carbohydrates are of plant origin, 

 being either cereals, sirups, vegetables, or fruits. 



