Post-Prandial Protein Handling: You Are What You Just Ate

BACKGROUND: Protein turnover in skeletal muscle tissue is highly responsive to nutrient intake in healthy adults. OBJECTIVE: To provide a comprehensive overview of post-prandial protein handling, ranging from dietary protein digestion and amino acid absorption, the uptake of dietary protein derived amino acids over the leg, the post-prandial stimulation of muscle protein synthesis rates, to the incorporation of dietary protein derived amino acids in de novo muscle protein. DESIGN: 12 healthy young males ingested 20 g intrinsically [1-(13)C]-phenylalanine labeled protein. In addition, primed continuous L-[ring-(2)H(5)]-phenylalanine, L-[ring-(2)H(2)]-tyrosine, and L-[1-(13)C]-leucine infusions were applied, with frequent collection of arterial and venous blood samples, and muscle biopsies throughout a 5 h post-prandial period. Dietary protein digestion, amino acid absorption, splanchnic amino acid extraction, amino acid uptake over the leg, and subsequent muscle protein synthesis were measured within a single in vivo human experiment. RESULTS: 55.3±2.7% of the protein-derived phenylalanine was released in the circulation during the 5 h post-prandial period. The post-prandial rise in plasma essential amino acid availability improved leg muscle protein balance (from -291±72 to 103±66 μM·min(-1)·100 mL leg volume(-1); P<0.001). Muscle protein synthesis rates increased significantly following protein ingestion (0.029±0.002 vs 0.044±0.004%·h(-1) based upon the muscle protein bound L-[ring-(2)H(5)]-phenylalanine enrichments (P<0.01)), with substantial incorporation of dietary protein derived L-[1-(13)C]-phenylalanine into de novo muscle protein (from 0 to 0.0201±0.0025 MPE). CONCLUSION: Ingestion of a single meal-like amount of protein allows ~55% of the protein derived amino acids to become available in the circulation, thereby improving whole-body and leg protein balance. About 20% of the dietary protein derived amino acids released in the circulation are taken up in skeletal muscle tissue following protein ingestion, thereby stimulating muscle protein synthesis rates and providing precursors for de novo muscle protein synthesis. TRIAL REGISTRATION: trialregister.nl 3638