Plasma Tryptophan Response Curve and Tryptophan Requirements of Elderly People

Abstract

Fourteen elderly subjects, four male and 10 female, 73 ± 5 years old, were studied for the relationships between plasma tryptophan concentration, tryptophan intake, and tryptophan requirement. The diet was based on an L-amino acid mixture, patterned as in egg protein, and provided N equivalent to 0.5 g protein/kg body weight. After an initial 5- to 10-day period at a tryptophan intake of 10 mg/kg/day (four subjects) or 5 mg/kg/day (10 subjects), there followed consecutive, isonitrogenous 4-day periods at graded reductions in tryptophan intake to 0.5 mg/kg/day. Fasting and 3½-hour postprandial plasma tryptophan levels were determined at the end of each diet period. Plasma tryptophan concentration decreased as tryptophan intake was reduced to the 2 mg/kg/day level. Thereafter, it remained relatively constant with further reductions in the intake level. These data indicate that the mean minimum tryptophan requirement of healthy, elderly subjects approximates 2 mg/kg body weight/day, lower than the value of about 3 mg/kg (J. Nutr. 101: 45, 1971) for young men found by the same procedure.