Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men

Background: 

The anabolic effect of resistance exercise is enhanced by the provision of dietary protein.

Objectives: 

We aimed to determine the ingested protein dose response of muscle (MPS) and albumin protein synthesis (APS) after resistance exercise. In addition, we measured the phosphorylation of candidate signaling proteins thought to regulate acute changes in MPS.

Design: 

Six healthy young men reported to the laboratory on 5 separate occasions to perform an intense bout of leg-based resistance exercise. After exercise, participants consumed, in a randomized order, drinks containing 0, 5, 10, 20, or 40g whole egg protein. Protein synthesis and whole-body leucine oxidation were measured over 4h after exercise by a primed constant infusion of [1-¹³C] leucine.

Results: 

MPS displayed a dose response to dietary protein ingestion and was maximally stimulated at 20g. The phosphorylation of ribosomal protein S6 kinase (Thr³⁸⁹), ribosomal protein S6 (Ser^240/244), and the ɛ-subunit of eukaryotic initiation factor 2B (Ser⁵³⁹) were unaffected by protein ingestion. APS increased in a dose-dependent manner and also reached a plateau at 20g ingested protein. Leucine oxidation was significantly increased after 20 and 40g protein were ingested.

Conclusions: 

Ingestion of 20g intact protein is sufficient to maximally stimulate MPS and APS after resistance exercise. Phosphorylation of candidate signaling proteins was not enhanced with any dose of protein ingested, which suggested that the stimulation of MPS after resistance exercise may be related to amino acid availability. Finally, dietary protein consumed after exercise in excess of the rate at which it can be incorporated into tissue protein stimulates irreversible oxidation.