THE PROTEINS 



Carbohydrates, whether of the starch group or of the sugar 



>up, are composed chiefly of three elements : carbon, hydro- 

 gen, and oxygen ; they are therefore combustible, and are great 

 energy producers. On the other hand, they are worthless for 

 cell growth and repair, and if we limited our diet to carbo- 

 hydrates, we should be like a man who had fuel but no engine 

 capable of using it. 



The fats. The best-known fats are butter, lard, olive oil 

 and the fats of meats, cheese, and chocolate. When we test 

 fats for fuel values by means of a calorimeter, we find that 

 they yield twice as much heat 

 as the carbohydrates (Fig. 36), 

 but that they burn out more 

 quickly. Dwellers in cold 

 climates must constantly eat 

 large quantities of fatty foods 

 if they are to keep their bodies 

 warm and survive the extreme 

 cold. Cod liver oil is an excellent food medicine, and if taken 

 in winter serves to warm the body and to protect it against the 

 rigors of cold weather. The average person avoids fatty foods 

 in summer, knowing from experience that rich foods make him 

 warm and uncomfortable. The harder we work and the colder 

 the weather, the more fatty food do we require; it is said 

 that a lumberman doing heavy out-of-door work in cold clim- 

 ates needs three times as much food as a city clerk. 



Most of our fats, like lard, butter, and cheese, are of animal 

 origin ; some of them, however, like olive oil, peanut butter, and 

 coconut oil, are of plant origin. 



The proteins. The proteins are the building foods, furnish- 

 ing muscle, bone, skin cells, etc., and supplying blood and other 

 bodily fluids. The best-known proteins are white of egg, curd 

 of milk, and lean of fish and meat. Most of our proteins are 



FIG. 36. a is the amount of fat neces- 

 sary to make one Calorie ; b is the 

 amount of sugar or protein necessary 

 to make one Calorie. 



