The anabolic response to a meal containing different amounts of protein is not limited by the maximal stimulation of protein synthesis in healthy young adults
Il-Young Kim American Journal of Physiology - Endocrinology and Metabolism Published 3 November 2015
We have determined whole body protein kinetics i.e., protein synthesis (PS), breakdown (PB), and net balance (NB) in human subjects in the fasted state and following ingestion of ~40g (moderate protein, or MP) that has been reported to maximized the protein synthetic response or ~70g (higher protein, HP) protein, more representative of the amount of protein in the dinner of an average American diet.
Twenty three healthy young men who had performed prior resistance exercise (X-MP or X-HP) or time-matched resting (R-MP or R-HP) were studied during a primed continuous infusion of L-[2H5]phenylalanine and L-[2H2]tyrosine. Subjects were randomly assigned into an exercise (X, n=12) or resting (R, n=11) group, and each group was studied at the two levels of dietary protein intake in random order. PS, PB, and NB were expressed as increases above the basal, fasting values (mg/kg LBM/min).
Exercise did not significantly affect protein kinetics and blood chemistry. Feeding resulted in positive NB at both levels of protein intake: NB was greater in response to the meal containing HP (p<0.00001). The greater NB with HP was achieved primarily through a greater reduction in PB and to a lesser extent stimulation of protein synthesis (for all, p<0.0001). HP resulted in greater plasma EAA responses (p<0.01) vs. MP, with no differences in insulin and glucose responses.
In conclusion, whole body net protein balance improves with greater protein intake above that previously suggested to maximally stimulating muscle protein synthesis because of a simultaneous reduction in protein breakdown.
