Human protein requirements: nitrogen balance response to graded levels of egg protein in elderly men and women

Abstract

Seven elderly men, ages 68 to 74 years, and seven elderly women, ages 70 to 84 years, participated in short-term studies to determine nitrogen balance response to graded intakes of whole egg protein within the sub-maintenance to near-maintenance range of nitrogen intake. After 1 week of consuming an adequate, free-choice diet, the subjects received a “protein-free” diet for 1 day to facilitate adaptation to a decreased level of dietary protein and three randomly assigned levels of egg protein for 10 days. A 4-day break with a normal diet followed each 10-day diet period. The levels of egg protein intake tested (gram protein (N × 6.25) per kilogram of body weight per day) were: for women, 0.52, 0.65, and 0.80 g and, for men, 0.57, 0.70, and 0.85 g. All the women were in negative nitrogen balance at the 0.52 g level of protein intake, and only two subjects achieved positive nitrogen balance at the higher intakes. Of the elderly men, four subjects were in positive balance at the 0.57 and 0.70 g levels, and five were in positive balance at the 0.85 g level. The calculated mean protein requirement for elderly women was 0.83 g of protein per kilogram per day, or twice the level arrived at by the factorial method (Scrimshaw, N.S., W.D.A. Perera and V.R. Young. J. Nutr. 106: 665, 1976). The factorial method thus fails to predict a suitable protein allowance for the elderly. It is concluded that a typical U. S. diet providing about 12 to 14% protein calories should be adequate for the elderly.