Comparative Nutritive Value of Casein and Lactalbumin for Man

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Abstract
Four normal adults were placed on a low protein diet for 12 days until a constant N excretion was reached. Four-day periods of supplementation with either casein or lactalbumin were then alternated with 4-day depletion pe-riods, the supplementation periods being repeated to mini-mize the effect of the antecedent conditions on the N balance. The N intake during the depletion periods was 0.008 g./kg./ day, and for the last 4 of the initial 12 days, the avg. N loss was 3.22 g. daily. The caloric intake during the 4-day study was maintained at 40 cals./kg. To attain positive N balance it was necessary to feed 0.033 g. N/kg. as the test protein (equal to 2% of the total cals). The expts. showed no sig-nificant difference between the capacities of the 2 proteins to maintain N balance in man. The avg. N loss for the 4 depletion periods was 3.07 g. Addition of casein spared 2.33 g. of body N, of lactalbumin, 2.31 g. The failure of methionine to improve the N retention of casein in man as in exptl. animals was attributed to the fact that man is not covered with hair.