American Journal of Clinical Nutrition, Vol 55, 959-962, Copyright © 1992 by The American Society for Clinical Nutrition, Inc

ORIGINAL RESEARCH COMMUNICATIONS

High-protein intake alters the response of fasting in normal human subjects

F Carraro and RR Wolfe
Metabolism Unit, Shriners Burns Institute, Galveston, TX 77550.

Two groups of normal volunteers were studied for 5 d of dietary control followed by 3 d of fasting. One group (n = 5) was given a control diet of 0.9 g protein.kg-1.d-1 and the other group (n = 7) was given a high- protein (HP) diet (2.5 g protein.kg-1.d-1). Both groups received 175.56 kJ.kg-1.d-1 (42 kcal.kg-1.d-1). The HP diet but not the control diet caused a significant retention of nitrogen. Postabsorptive leucine kinetics as assessed with [1,2-13C]leucine were similar in the two groups. In the control subjects, the rate of nitrogen excretion did not change in response to fasting, but leucine oxidation increased. In contrast, nitrogen excretion progressively decreased with fasting after the HP diet. Leucine rate of appearance was increased after fasting after the HP diet but oxidation was not increased, meaning that the calculated rate of whole-body protein synthesis was higher than in the control group. The response to a short period of food deprivation is dependent on prior protein intake.