PROTEIN-REQUIREMENTS OF ELDERLY MEN

The egg protein requirements of men over age 60 were determined by the same techniques previously used to establish requirements of younger men, in the same laboratory. The six subjects were healthy but somewhat obese; their basal metabolic rates, lean body mass, and urinary creatinine excretion were 12 to 15% less than values for young men of about the same height. They were given a protein-free diet for 17 days to determine endogenous nitrogen (N) losses, with energy sufficient to maintain body weight (BW) nearly constant. Endogenous fecal and urinary N losses were 0.79 ± 0.18 and 2.27 ± 0.22 g/day, respectively. Endogenous urinary N was equivalent to 27 ± 2 mg/kg BW, 1.45 ± 0.20 mg/basal kcal, 1.64 ± 0.15 g/g creatinine, and 43 ± 1 mg/kg lean body mass (LBM). The value for elderly men was less than that for young men per day and per kg BW, but the same when expressed in relation to creatinine excretion, LBM, and basal energy. In two sequential periods, eggwhite protein was given in amounts equal to 1.34 to 1.88 times the measured endogenous nitrogen output. Urinary, fecal, integumental, and miscellaneous N losses were measured to determine true balance. The minimum dietary requirement to maintain N equilibrium was computed from regression analysis of balances at the three levels of intake. Average N requirement was predicted to be 6.16 ± 0.24 g/day; this is equal to 74 mg/kg actual BW or 88 mg/kg 'ideal' BW (standard for height at age 25). Minimum requirement was not correlated with BW, creatinine, basal metabolic rate, or height, but was associated with the magnitude of the endogenous loss and the efficiency of protein utilization. The 'safe level' of egg protein for healthy older men, as defined by the FAO/WHO, i.e., the average N requirement for balance plus 2 standard deviations, was calculated to be 95 mg N or 0.59 g protein/kg ideal BW, under the conditions of this study. This figure is negligibly higher than the present FAO/WHO 'safe level' of 0.57 g egg protein/kg reference weight.