CHAPTER XI 



NUTRITION 



The choice of a diet is primarily a question of instinct. 

 But instinct, while it can be trusted to provide a sufficiency 

 in amount, may err in providing too much or in not pro- 

 viding a sufficiency in kind. In order that the diet may 

 be adequate for the proper performance of the bodily 

 functions, it must be sufficient in amount as a source of 

 energy, and in kind as containing in proper amount all 

 those substances which are necessary for the maintenance 

 of the body structure and which cannot be synthesised in 

 the body. The best diet is that which fulfils these functions 

 with the most economical working of the digestive apparatus. 



THE CARBON BALANCE 



Assuming that the food is of such a nature as to provide 

 adequately for the maintenance of the machine, we can 

 inquire as to the amount and form in which it is best suited 

 as a source of energy. As to the amount, this can be 

 determined by comparing the carbon taken in as food and 

 the carbon excreted. If these are equal the individual is 

 in a condition of carbon balance, and the food is sufficient 

 as a source of energy. If intake is in excess of output the 

 energy supply is more than sufficient and storage is taking 

 place. If output is in excess of intake the food is insufficient 

 and the body is hving upon the stores previously accumu- 

 lated or upon the tissues themselves. 



The following figures may be taken as showing the 

 amounts of the three main classes of foods habitually eaten, 



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