LIMIT OF PROTEIN REQUIREMENT. 915 



subject. In one of the periods 16.27 grams N, 44 grams fat, and 466 

 grams carbohydrate were given; in a second, 16.08 grams N, 140 grams 

 fat, and 250 grams carbohydrate, containing almost the same number 

 of calories, namely, 2867 and 2873. In both cases an almost complete 

 nitrogenous equilibrium was reached and the carbohydrate did not 

 spare more protein than the fat. It is therefore possible that the fat has 

 about the same protein-sparing action as an isodynamic amount of car- 

 bohydrate when the quantity of carbohydrates does not sink below a 

 certain minimum, which is not known for the present. 



This condition as well as the extent of protein-sparing action of the 

 carbohydrates stands, according to LANDERGREN, in close relation to 

 the formation of sugar in the body. The animal body always needs 

 sugar, and a lack of carbohydrates in the food leads to a part of the pro- 

 teins being used in the sugar formation. This part can be spared by 

 carbohydrates but not by fats, from which, according to LANDERGREN, 

 the carbohydrates cannot be formed. In this also lies the probable 

 reason why the fats, on being fed exclusively but not with a sufficient 

 supply of carbohydrates, have a much lower protein-sparing action than 

 the carbohydrates. The fats cannot prevent the protein catabolism 

 necessary for the formation of sugar on a diet lacking in carbohydrates. 



The law as to the increased protein catabolism with increased pro- 

 tein supply also applies to food consisting of protein with fat and car- 

 bohydrates. In these cases the body tries to adapt its protein catabolism 

 to the supply; and when the daily calorie-supply is completely covered 

 by the food, the organism can, within wide limits, be in nitrogenous 

 equilibrium with different quantities of protein. 



The upper limit to the possible protein catabolism per kilo and per 

 day has been determined only for herbivora. For human beings it is 

 not known, and its determination is from a practical standpoint of second- 

 ary importance. What is more important is to ascertain the lower limit, 

 and on this subject we have several older experiments upon man as well 

 as upon dogs by HIRSCHFELD, KUMAGAWA, KLEMPERER, MUNK, ROSEN- 

 HEiM, 1 and others. It follows from these experiments that the lower 

 limit of protein requirement for human beings, for a week or less, is about 

 30-40 grams or 0.4-0.6 gram per kilo with a body of average weight, 

 v. NooRDEN 2 considers 0.6 gram protein (absorbed protein) per kilo 

 and per day as the lower limit (threshold of protein requirement). The 

 above-mentioned figures are valid only for short series of experiments; 

 still there exists the observation of E. VOIT and CONSTANTINIDI 3 on 



1 See footnote 3, page 903; also Munk, Arch. f. (Anat. u.) Physiol., 1891 and 1896 

 Rosenheim, ibid., 1891; Pfluger's Arch., 54. 



2 Grundriss einer Methodik der Stoffwechseluntersuchungen. Berlin, 1892. 

 Zeitschr. f. Biologic, 25. 



