136 DAIRY CHEMISTRY 



ized by containing a larger amount of carbon than 

 either starch or sugar, and hence, when burned or 

 digested in the body, they produce a larger amount 

 of heat and energy. A pound of fat will produce 

 2.25 times as much heat as a pound of starch. 



131. Digestible Nutrients. — Only a portion of the 

 compounds of which foods are composed is digested, 

 absorbed by the body, and used for some functional 

 purpose. In average food stuffs from 15 to 45 per 

 cent of the nutrients are indigestible and unavailable 

 to the body. That portion of a compound which 

 is digested and utilized is called a digestible 

 nutrient. Foods contain digestible protein, digest- 

 ible fats, and digestible carbohydrates. The total 

 nutrients are only in part digestible. The digestible 

 nutrients of a food stuff are determined by means of 

 digestion experiments, in which the income and outgo 

 of the nutrients of the food, including the amount 

 which fails to digest, are accurately determined. As 

 a result of numerous digestion experiments, the 

 digestion coefficients or the percentage of the nu- 

 trients that are digested are determined. The diges- 

 tion coefficients are used for the construction of 

 tables of digestible nutrients in foods. In using 

 these tables in rational feeding, it is only the digest- 

 ible nutrients that are to be considered, as the in- 

 digestible portion of the food furnishes no material 

 for functional purposes. 



132. Caloric Value or Heat Units of a Ration. — 

 When food is digested, heat is produced and the 



