HUMAN STRUCTURE AND LIFE-ACTIVITIES 497 



Many experiments with different combinations of foods 

 have led to the conclusion that men of about 150 pounds 

 T ght engaged in sedentary work require food yielding from 

 to 2400 calories per day of 24 hours. Men doing hard 

 ysical work for eight hours per day require food furnishing 

 m 3000 to 4000 calories ; and very hard work may require 

 >re than 5000 calories. There are individual variations 

 long men of equal weight doing. the same work. Some idea 

 the meaning of these figures will be gained from the state- 

 ment that 100 grams of protein food giving 400 calories, 

 100 grams of fat giving 900 calories, and 250 grams of car- 

 bohydrates giving 1000 calories makes a total of 2300. This 

 would suffice for a professional man or a shoemaker, but a 

 ijrmer, mason or carpenter would require more fat and 

 . rbohydrate food daily. 



420. Foods for Muscular Work. It was formerly 

 upposed that protein foods are necessary for muscular 

 work, and we frequently hear that " laborers must eat much 

 meat in order to get strength to work." This is not true. 

 It has been shown that muscular exercise does not require 

 more protein food, for fats or carbohydrates can furnish the 

 necessary extra energy. Two physiologists who used a 

 mixed diet of proteins and the other foods have proved that 

 their bodies oxidized as much protein on a day of rest as 

 on a day when they climbed a mountain over 6000 feet 

 high; and also that the amount of energy in the protein 

 they oxidized was not sufficient to lift their bodies so high. 

 Hence the other foods (fats and carbohydrates) eaten must 

 have supplied the necessary extra energy. But if these men 

 had eaten more pure protein, they could have gotten from 

 it the necessary energy. 



The conclusion from many such experiments is that large 

 amounts of protein are not needed for ordinary work. The 

 necessary amount is approximately the same for every day, 

 whether keeping quiet or working, and is from 60 to 100 



2K 



