Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men.
Level 2 - randomized trial
Controlled clinical trial evaluating acute metabolic interventions in humans
PubMed 22451437 · doi:10.1113/jphysiol.2012.228833
What was done
Twenty-four males completed an acute bout of unilateral resistance exercise and consumed one of three post-exercise protein formulations: 25 g whey protein (WHEY), 6.25 g whey protein supplemented with leucine to match the total leucine in WHEY (LEU), or 6.25 g whey protein supplemented with essential amino acids (EAAs) to match WHEY for all EAAs except leucine (EAA-LEU). Myofibrillar protein synthesis (MPS), mTOR signalling, and amino acid transporter (AAT) mRNA abundance were measured in the fasted state (FAST) and after feeding under rested (FED) and post-exercise (EX-FED) conditions.
What was found
Leucinaemia was equivalent between WHEY and LEU and significantly higher than EAA-LEU (P = 0.001). At 1–3 h post-exercise, MPS increased significantly above FAST in both FED (P < 0.001) and EX-FED (P < 0.001) conditions with no treatment effect. At 3–5 h, only WHEY remained significantly elevated above FAST in EX-FED (WHEY 184% vs. LEU 55% and EAA-LEU 35%; P = 0.036). Feeding and exercise increased AAT mRNA abundance above FAST with no effect of leucinaemia.
Why it matters
Supplementing a suboptimal 6.25 g protein dose with leucine or EAAs stimulates early (1–3 h) muscle protein synthesis as effectively as 25 g intact whey, but 25 g whey protein is required to sustain elevated synthesis rates through 3–5 h post-exercise.
Limits
The study sample was small (n = 24) and included only males. It measured acute, single-bout fractional synthetic rates up to 5 h rather than chronic resistance training adaptations or whole-body protein balance.
Cited by
- supports Adding supplemental leucine to a suboptimal or low-protein dose stimulates muscle protein synthesis to a level comparable to a higher-protein dose.