502 THE HUMAN BODY 



(|-j? oz.). Theoretically it should be possible to sustain life 

 indefinitely on a diet containing this amount of protein, provided 

 adequate fats and carbohydrates for the fuel requirements of the 

 Body are also furnished. This theoretical minimum of protein 

 does not agree at all well with the amounts of protein actually 

 consumed. In fact dietary studies show that most people take 

 four to five times this amount. The great discrepancy between 

 the amount of protein theoretically required and that actually 

 ingested has occasioned a great deal of discussion among dietitians 

 as to whether the human race is habitually consuming proteins 

 to excess. Since the proteins are the most expensive food stuffs 

 the question is one of great economic importance. 



Numerous experiments have been performed to see what is 

 the effect of cutting the protein intake approximately to the 

 theoretical minimum. In all the early experiments along this 

 line when the protein content of the diet was reduced to about 

 35-40 grams daily, a figure well above the theoretical minimum, 

 the tissue wear and tear was no longer made good completely. 

 This was evidenced by the daily elimination from the Body of 

 more nitrogen than was taken in. The only possible source of 

 the excess was from break-down of the Body's own tissues. There 

 was also a steady loss of body weight. When an explanation of 

 this was sought it was found that the chief difficulty lay in the 

 manner of administering the protein. This substance when taken 

 with the diet in the usual rather large amounts functions in part 

 to replace worn-out tissues and in part, as we have seen, as fuel 

 for supplying energy, the latter use being made of all surplus after 

 the tissue repair has been provided for. The wear and tear of 

 tissues goes on throughout the twenty-four hours of the day. The 

 ordinary method of taking the protein, on the other hand, is in 

 three meals during the daytime portion of the day. When the 

 consumption is cut down to a low level evidently if there is any 

 use of protein as fuel a shortage for tissue repair is likely to occur. 

 When the protein is ingested in connection with the usual meals 

 there is absorbed into the Body after each an amount which is in 

 excess of the immediate needs for tissue repair, and accordingly 

 some is used as fuel. The result is that before the time for the 

 next meal arrives all the absorbed protein is used up and there is 

 none to carry on the work of tissue repair. To avoid this the 



