Association of postprandial postexercise muscle protein synthesis rates with dietary leucine: A systematic review.
Level 1 - systematic review of randomized trials
Systematic review of human interventional trials measuring postexercise muscle protein synthesis
PubMed 37537134 · doi:10.14814/phy2.15775
What was done
A quantitative systematic review evaluated data from studies where healthy adults performed a bout of resistance exercise, ingested a protein bolus within one hour post-exercise, and had plasma leucine variables (peak magnitude, rate of rise, and total availability) and muscle protein synthesis (MPS) rates (delta change from basal) measured.
What was found
Ingested leucine dose was significantly associated with postprandial postexercise MPS response in older adults in the acute phase (0–2 h, r² = 0.64, p = 0.02) and over the entire postprandial period (>2 h, r² = 0.18, p = 0.01), but not in younger adults. No single plasma leucine variable possessed substantial predictive capacity over the magnitude of MPS rates in younger or older adults, and no distinct leucine threshold was identified in older adults.
Why it matters
These findings challenge the "leucine trigger" hypothesis that plasma leucine kinetics determine postexercise anabolism, indicating that total ingested leucine dose drives muscle protein synthesis primarily in older adults.
Limits
The abstract does not disclose the total number of included studies or participants, sex distribution, protein sources, or resistance exercise parameters. Results reflect aggregate study-level associations rather than an individual participant data analysis.
Cited by
- context Approximately 2.5 to 3 grams of the amino acid leucine is required per meal to trigger muscle protein synthesis.