THE ABSORPTION AND USE OF FOODS 453 



actually used for fuel loses its nitrogen and becomes indistinguish- 

 able from carbohydrate long before it is used. It has been sug- 

 gested that the animal world has always had more protein in its 

 diet than was necessary for tissue repair, and so has developed 

 the rather complex machinery for making use of the surplus as 

 fuel; till now the mechanism works so well that if the food does 

 not contain protein upon which it can expend itself it performs its 

 function at the expense of the body tissues themselves. This 

 idea, while interesting, cannot be proven, and must not, therefore, 

 be viewed as having much weight. 



Although physiologists are virtually agreed that the minimum 

 protein requirement of the Body is in excess of the tissue-repair 

 requirement, they are not agreed as to its actual amount. The 

 earlier physiologists and many modern ones place it between 

 100 and 120 grams per day. Others consider those figures exces- 

 sive, and place the requirement lower, the extreme low limit 

 being placed at 30 to 40 grams per day. In view of these di- 

 verging opinions we may well inquire what is the amount of pro- 

 tein ordinarily taken per day by civilized man. A large series of 

 estimations made some years ago in Europe gave the average 

 daily protein consumption as 118 grams. Some recent estima- 

 tions by American college students indicate that in this country 

 the average is somewhat lower, probably about 90 grams. That 

 all the actual protein needs of the Body can be satisfied with 30 or 

 40 grams daily intake has been demonstrated by several observ- 

 ers. Whether it is therefore desirable to reduce the protein to 

 that amount is quite another question, and one which is at present 

 under active discussion. In the absence of more information on 

 the subject the safe practical course is probably to continue our 

 present habits so far as amounts of the various foods to be eaten 

 are concerned, but bearing in mind that moderation in the use 

 of proteins is certainly not harmful and may be distinctly ad- 

 vantageous. 



It must be noted that in estimating the amount of food to be 

 taken to satisfy the energy requirements of the Body it is per- 

 missible to compute all the protein as though it served as fuel, 

 disregarding the fact that part of it is used for tissue repair. This 

 can be done because although the work of restoring the worn-out 

 tissues is part of the total work of the Body, and the energy re- 



