Post-Prandial Protein Handling: You Are What You Just Ate.
Level 4 - case-series / case-control
Uncontrolled before-and-after physiological isotope tracer study in a single group of healthy volunteers
PubMed 26556791 · doi:10.1371/journal.pone.0141582
What was done
Twelve healthy young men ingested 20 g of intrinsically [1-13C]-phenylalanine-labeled protein during primed continuous infusions of L-[ring-2H5]-phenylalanine, L-[ring-2H2]-tyrosine, and L-[1-13C]-leucine. Arterial and venous blood samples and skeletal muscle biopsies were gathered over a 5-hour postprandial period to measure dietary protein digestion, amino acid absorption, splanchnic extraction, leg amino acid uptake, and muscle protein synthesis within a single in vivo protocol.
What was found
During the 5-hour period, 55.3±2.7% of dietary protein-derived phenylalanine was released into the circulation. Postprandial essential amino acid availability shifted 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 rose from 0.029±0.002 to 0.044±0.004%·h⁻¹ (P<0.01), with dietary L-[1-13C]-phenylalanine directly incorporating into de novo muscle protein from 0 to 0.0201±0.0025 mole percent excess.
Why it matters
This study provides an end-to-end quantitative demonstration in humans that roughly 55% of dietary amino acids from a single meal-like protein bolus reach systemic circulation and directly serve as building blocks for de novo skeletal muscle synthesis.
Limits
The sample size was small (n = 12) and limited to young healthy men. The protocol examined a single resting 20 g dose over a 5-hour period, leaving open how kinetics differ with other doses, exercise, or in females and older adults.
Cited by
- supports Following ingestion of 20 grams of protein, approximately 10 grams of amino acids are released into the systemic circulation over the subsequent 4 hours.