456 THE HUMAN BODY 



more fat is present. For this reason it is desirable to limit some- 

 what the amount of fat used. 



Another question which may affect the choice of foods is the 

 degree to which they tax the excretory organs of the Body. We 

 have seen that fuel proteins yield an ammonia residue in absorp- 

 tion, which must be gotten rid of by the excretory organs. There 

 seems to be a rather general belief that this task constitutes a 

 somewhat serious strain upon these organs, and if it does tend to 

 throw upon them excessive labor it is clear that the consumption 

 of proteins ought on this account to be kept as low as possible. 

 The idea that the excretory organs are endangered by ordinary 

 amounts of protein in the diet is not sustained by any very con- 

 vincing evidence, although that excessive protein consumption 

 may be harmful is quite well established. 



In the matter of cost, which must also be taken into considera- 

 tion, carbohydrates have a marked advantage over the other food- 

 stuffs. For example, bread, which is chiefly carbohydrate, yields, 

 dollar for dollar, about ten times as many Calories as lean beef, a 

 protein. The cheapest proteins are the vegetable ones; a given 

 weight of protein costing about five times as much when bought 

 as beef as when purchased in the form of beans. 



The final factor to be taken into account is the appetizing 

 quality of the different foods. The dependence of the whole di- 

 gestive process upon a proper initial psychic secretion of gastric 

 juice emphasizes the importance of the use of appetizing foods. 

 Boiled meat contains as much nourishment as the same weight 

 of roasted meat, but the former is less desirable as a food because 

 the process of boiling extracts from it the substances which impart 

 to meat its flavor. Eggs are exceedingly nutritious, but to some 

 people they are practically valueless as food, because they inspire 

 aversion rather than appetite. 



From these various considerations we may summarize the gen- 

 eral rule that the choice of food should be such as to yield sufficient 

 protein for the Body's protein requirement, without containing an 

 amount so excessive as to throw an undue burden on the excretory 

 organs; that the amount of fat should be somewhat limited; and 

 that enough carbohydrate should be added to bring the sum total 

 up to the Body's energy requirement; finally, that the most ap- 

 petizing foods obtainable within a reasonable limit of cost should 



