HUMAN FOODS. 195 



All nutrients yield energy in form of heat and musculaf 

 strength. 



In being themselves burned to yield energy the nutrients 

 protect each other from being consumed. The protein and 

 fats of body tissue are used like those of food. An impor- 

 tant use of the carbohydrates and fats is to protect protein 

 (muscle, etc.) from consumption. 



Definition of Food and Food Economy. — The views thus 

 presented lead to the following definitions: (i) Food is 

 that which, taken into the body, builds tissues or yields 

 energy; (2) the most healthful food is that which is best 

 fitted to the wants of the user; (3) the cheapest food is that 

 which furnishes the largest amount of nutriment at the 

 least cost; (4) the best food is that which is both most 

 healthful and cheapest. 



We have, then, to consider the kinds and amounts of 

 nutrients in different food materials, their digestibility, and 

 the kinds and amounts needed for nourishment by people 

 doing different kinds of work. 



In general, the animal foods have the most of protein 

 and fats, while the vegetable foods are rich in the carbo- 

 hydrates, starch, and sugar. The lean meats and fish 

 abound in protein. Cheese has so large a quantity of 

 protein because it contains the casein of the milk. Among 

 the vegetable foods, beans and peas have a high proportion 

 of protein. The proportion in oatmeal is also large. In 

 wheat it is moderate, and in corn meal it is rather small. 

 The materials with the highest fuel value are those with 

 the most fat, because the fuel value of the fat is, weight 

 for weight, two and one-fourth times as great as that of 

 either sugar, starch, or protein. Hence fat pork and butter 

 lead the other materials in fuel value. The fat meats in 

 general stand high in this respect. So also do the grains, 

 flour, and meal, as they have large quantities of carbo- 

 hydrates. Potatoes are quite low in the list in respect to 

 fuel value as well as protein, principally because they are 

 three-fourths water. For the same reason, milk, which is 

 seven-eighths water, ranks low in respect to both protein 

 and fuel value. 



