No. 6. 



DEPARTMENT OF A<".iaCUT.TURE 



996 



THE FUNCTIONS AND USES OF FOODS.* 



BY C. v. LANGWOKTHY, PH. D.. O./icc of ExptiiiiifiU SlaUons. 



Circular Xo. 46, United Slates J)epai'tinent of Agriculture. 



Ordinar-y food materials, sueli as meat, fish, eggs, potatoes, wheat, 

 etc., consist of — 



Refuse. — As the bones of meat and fish, shells of shellfish, skins 

 of potatoes, bran of wheat, etc. 



Edible I'ortion.— As the flesh of meat and fish, the white and joWi 

 of eggs, wheat flour, etc. The edible portion consists of water and 

 nutritive ingredients, or nutrients. The- nutritive ingredients are 

 protein, fats, carbohydrates and mineral matters. 



The water, refuse and salt of salted meat and fish are called non- 

 nuti-ients. In comparing the values of dill'erent food materials for 

 nourishment they are left out of account. 



Use of Nutrients. 



Food is used in the body to build and repair tissue and to furnish 

 energy. The manner in whicli the valuable constituents are utilized 

 ill the body may be expressed in tabular form as follows: 



Protein Forms tISFuc (muscles, tendon, 



AVhite (albumen) of eggs, curd and pro!. ably fat), 

 (casein) of milk, lean meat, 

 gluten of wheat, etc. 



Fats Form fatty tissue. 



Fat of meat, butter, olive oil, 

 oils of corn and wheat, etc. 



Carbohydrates Transformed into fat. 



Sugar, starch, etc. 



Mineral matters (ash) .Aid in forming bone, assist in 



Phosphates of lime, potash, digestion, etc. 

 soda, etc. 



All serve as fuel and 

 -yield energy in form of heat 

 and muscular strength. 



*This article, which was originally published under the title "Foods for Man," in the U. S. 

 Bept. Agr. Yearbook, 1897, pp. 676-6S2, has been revised and contains some additional matter. 



The Fuel Value of Food. — Heat and muscular power are forms of 

 force or energy. The energy is developed as the food is consumed 

 in the body. The unit commonly used in this measurement is the 

 calorie, the amount of heat which would raise the teinjterature of 

 a pound of wat(n- 4 degrees F. 



Instead of this unit, some unit of mecdianical energy might be 

 used— for instan<-e, the foot -Ion, whi(di represents ihf force re- 



