354 FOOD AND NUTRITION 



Chemists have analyzed nearly every food, and have deter- 

 mined its heat-producing ability by burning in a calorimeter 

 (Art. 122). The results of these investigations on some of the 

 common foods are given (page 353). By reference to Table 

 XIV, it is an easy matter to see just what food principles 

 each food furnishes the body, what proportion of the food 

 principles is furnished, and just how much energy, measured 

 in greater calories, is furnished. 



392. Some Observations on the Table. It is evident to 

 anyone who will study the table that some of our foods contain 

 much water. Their calorific value is, therefore, rather low. 



Watermelon, for instance, contains over 

 92 per cent, water and its heat value is 

 but 136 Cal. per Ib. while butter con- 

 tains about 13 per cent, water and its 

 calorific value is 3600 Cal. per Ib. This 

 must mean that butter is a much better 



FIG. 249. Composition . .. ,, , . ., , . 



of butter. fuel for the body than watermelon. A 



man could scarcely eat enough water- 

 melon to supply the energy needs of his body, while a rather 

 small amount of butter would meet the energy demands easily 

 (Fig. 249), 



It is also evident that some foods are much richer in certain 

 of the food principles than others. Thus butter contains about 

 85 per cent, fat and no carbohydrate, while sugar contains 100 

 per cent, carbohydrate and no fat. The cereals are all rich 

 in carbohydrate while their fat and protein percentages are 

 rather low. The meats, on the other hand, contain, as a rule, 

 no carbohydrate while their percentages of fat and protein are 

 rather high. In general, fruits contain much water, little 

 protein and fat, and relatively much carbohydrate. In 

 selecting foods, then, a knowledge of their composition is 

 necessary. 



393. The Heat Value of the Food Principles. When the 

 pure food principles are burned in the calorimeter it is found 

 that they produce the following amounts of heat: 



