SECTION III 

 THE EFFECT OF FOOD ON METABOLISM 



DURING the starvation the energy requirements of the animal are supplied 

 by the actual consumption of the tissues of the body. When food is taken 

 it has to supply the losses effected in this way. It is convenient however 

 to consider food as having a twofold destiny, viz. (1) to supply the energy 

 necessary to maintain the body alive and for the performance of work; 

 (2) to replace the wear and tear of the body. So far as the latter function 

 is concerned the proteins of the food take a position apart from the other 

 two classes fats and carbohydrates. Every working cell of the body 

 and every muscle fibre consist for the most part of proteins with only small 

 amounts of fats and carbohydrates. To repair the wear and tear of the 

 machine of the body therefore proteins are absolutely necessary. To 

 supply the energy requirements of the body any or all of the three classes 

 of foodstuffs can be utilised. 



A starving man is diminishing in weight and is putting out energy as a 

 result. In the example cited on p. 672 the man was losing about 13 grm. 

 nitrogen a day and was putting out about 2000 Calories. These Calories 

 came partly from the combustion of protein and partly from the oxidation 

 of the fat. It would manifestly be useless to try to stay the loss from the 

 body by giving the man 13 grm. of nitrogen in the food in the form of 

 protein, since this would give him only 320 Calories towards his basal 

 requirements of 2000. We should find, in fact, that the effect of such an 

 administration would be practically to double the output of nitrogen from 

 the body and to increase slightly the total output of energy. In the dog it 

 would be possible to stop the diminution of the body weight and the waste 

 of tissues by giving an amount of protein equal to five times the loss during 

 starvation. In man such an amount would be too great for his assimilating 

 powers, and it would be necessary to give in addition to the protein fats 

 and carbohydrates. Since the body reacts somewhat differently to these 

 three different classes of foodstuffs, it will be convenient to deal with them 

 separately. 



THE INFLUENCE OF PROTEINS 



The protein taken in with the food on a pure protein diet has a twofold 

 function to perform. In the first place, every functional activity of the 

 living tissues is probably associated with a certain amount of wear and tear, 

 and results in the production of disintegration products which arc not in a 

 condition to be resynthetised into living working protoplasm. We know 



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