THE NORMAL DIET OF MAN 733 



3 to 4 grin, of nitrogen per day, i.e. between 25 to 35 grm. of protein. 

 Other observations have been made on vegetarians, showing that 

 individuals can maintain perfect health on a diet containing only 

 about 34 grm. of protein a day, and with a total calorie value of 1400 

 to 2000. A series of experiments have lately been conducted by 

 Chittenden with a view to determining how far such a diet is suitable 

 to the average individual, and especially whether it can be continued 

 for long periods of time without interfering with the well-being of 

 the subject of the experiment. The general results of these experi- 

 ments show that the physiological needs of the body can be met 

 by greatly reduced protein intake with the establishment of continued 

 nitrogenous equilibrium on a far smaller amount of protein food than 

 is contained in the ordinary dietary tables, and that on this diet the 

 individual in some cases, far from suffering in health, has his physical 

 and mental efficiency increased. The experiments were made on 

 various classes of men : instructors and students in the university, 

 soldiers, and athletes. In the case of Chittenden himself the average 

 daily diet contained about 6 grm. of nitrogen and had a heat-value 

 of about 1600 calories. In the case of another individual the intake 

 of .nitrogen per day was 9*5 grm. and the heat-value of the food 

 2500 calories. It is thus possible to reduce the total energy of the 

 food from about 3300 calories to about 2500 calories. Of the protein 

 taken in by a normal individual therefore a certain amount which is 

 not needed by the organism is at once broken up and serves simply 

 to increase the total metabolism of the body without serving any 

 useful physiological purpose other than heat production.* J(Iany 

 ailments, especially of middle age, have been ascribed to an excess 

 of protein in the food. It has been thought that the kidneys and 

 other organs may suffer from the strain of eliminating excess of 

 nitrogenous waste products. But the energy metabolism of proteins 

 results almost entirely in the formation of urea an innocuous sub- 

 stance which can have little harmful effect on the kidneys, even if 

 we assume (an assumption hardly justifiable ) that these organs 

 (unlike other organs of the body) suffer as a result of their normal 

 functional activity. There is no doubt that many disorders of 

 middle life may be put down to over-feeding and lack of muscular 

 exercise, but there is just as much reason to ascribe these evils to 

 the carbohydrates as to the proteins of the diet. It is indeed possible 

 that an almost exclusive protein diet might be more suitable than 

 carbohydrates for a sedentary life, where the normal stimulus to 

 oxidation of the food-stuffs, viz. muscular exercise, is absent, and 



* But heat production is a very important function of the food, and on the 

 Chittenden diet tends to be deficient ; so that individuals on this regime * feel 

 the cold ' more than they did when on an ordinary diet. 



