THE PROTEIN REQUIREMENTS OF MANKIND U3 



scales, etc., all that is required by the system ? If so, then a 

 few grammes of protein daily is all that is absolutely essential. 

 In other words, are we justified in believing that a diet should 

 contain only the minimum amount of protein on which nitrog- 

 enous equilibrium can be established ? If we are not justified 

 in this belief, and admit that an extra quantity above this 

 minimum is for the welfare of the body, then where is the line 

 to be drawn ? The question at once arises, if a small extra 

 amount of protein beyond actual requirements, Rubner's margin 

 of safety, is to the advantage of the protein- containing tissues, 

 will a larger quantity an increased margin of safety not be to 

 their still greater advantage ? 



The answer to these inquiries can only be sought in metabolism 

 experiments and dietary studies not undertaken with a view of 

 showing the possibility of man subsisting and doing a certain 

 amount of work on a protein intake of one-third to one-half that 

 of Voit's standard, but carried out on a large scale, under varying 

 conditions, and over long periods of time, with the object of 

 determining the effects of a low protein dietary on man's bodily 

 and mental efficiency, susceptibility to disease, and general 

 well-being. 



To a consideration of the evidence that has, and is being, 

 accumulated on this important problem we shall now turn. 

 Chittenden's views and the opinions of those who uphold the merits 

 of diets poor in protein are too well known to require detailed 

 exposition ; only a short synopsis, therefore, will now be given 

 of the work that has been done from this standpoint, reserving 

 for the following chapters its consideration and an account of 

 the results obtained by later observers. 



EXPERIMENTAL RESULTS OBTAINED WITH MAN AS REGARDS THE 

 EFFECTS OF DIETS POOR IN PROTEIN. 



There are a large number of scattered observations throughout 

 the literature of metabolism dealing with the lower limits of 

 protein intake. In the earlier experiments, when the protein 

 intake was small in amount, the fuel value of the diet was high, 

 and it was found that a large supply of non-nitrogenous food 

 materials allows the organism to accommodate itself easily to 

 a low protein dietary. Siven* was the first to reduce the energy 

 value of the diet to moderate proportions even when the protein 

 * V. Noorden, " Physiology of Metabolism," p. 300. 



