DIGESTION AND NUTRITION 



331 



and for other factors that are known and under 

 control. 



The approximate amount of energy which a food will 

 yield can be determined by the use of the following fac- 

 tors : Ether extract 4225, and fiber, nitrogen-free ex- 

 tract, and crude protein 1860. These are the numbers of 

 calories which a pound of each of the nutrients yields. 



452. Available Energy of Foods. Since only a por- 

 tion of the nutrients of foods is digesti- 

 ble, not all of the total caloric value 

 is rendered available to the body. 

 The digestion process is more com- 

 plete with non-nitrogenous compounds 

 than with the proteids. The final 

 products of oxidation in the case of 

 starch, sugar and digestible carbohy- 

 drates are carbon dioxid and water. 

 These compounds undergo complete 

 combustion. The final products of di- 

 gestion of the proteids are amides, the 

 larger portion of which is excreted as 

 urea in the liquid waste. This com- 

 pound, urea, CH 4 N 2 O, does not un- 

 dergo complete oxidation in the body. 

 If burned in the calorimeter, it would 

 yield an additional amount of heat. 

 The term available energy of a food 

 means simply the total energy avail- Fi e- 9?. 



able to the body and measured in calories. The 

 available energy is obtained by deducting from the 



