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

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 x 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. Am. I. Clin. Nutr. 31: 779-785, 1978. Current dietary protein allowances for the elderly are based on extrapolations of data obtained from healthy young adults (1, 2). However, age-related changes in body protein metabolism suggest that dietary protein needs may change with advancing age in humans. It is particularly important to examine this possibility because of the growing number of elderly people in North America and other industrialized regions (e.g., Reference 3). A review of the studies concerned with assessing the dietary protein needs for older people does not allow definitive conclusions concerning their requirements relative to those of healthy young adults (e.g., References 4 and 5). Some investigators have concluded that the elderly need more dietary protein than younger people (6), whereas others have concluded that they require similar amounts (7, 8) or less (9). The discrepancies among the various studies presumably relate to differences in the types of subjects studied, the methods chosen to estimate needs, or the interpretation of the experimental findings. We have begun a systematic investigation of protein metabolism and nutrition in healthy elderly subjects. We first determined the obligatory urinary and fecal nitrogen losses for healthy females (10) and males (11) and, by applying the Food and Agriculture Organization/World Health Organization (FAO/WHO) factorial method (2) with correction factors for efficiency of utilization of dietary protein and normal ‘From the Department of Nutrition and Food Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. 2 Supported in part by Grant AG00475 from the National Institutes of Health. The Clinical Research Center is supported by a grant (RR-88) from the General Research Centers Program of the Division of Resources, National Institutes of Health. ‘ Address reprint requests to: Dr. Vernon R. Young, 56-331, M.I. T. , Cambridge, Mass. 02139. by on A ril 4, 2008 w w w . an.org D ow nladed fom