Co-ingestion of leucine with protein does not further augment post-exercise muscle protein synthesis rates in elderly men.
Level 2 - randomized trial
Randomized crossover trial in humans
PubMed 17697406 · doi:10.1017/S0007114507812013
What was done
Eight elderly men (mean age 73 +/- 1 years) were randomly assigned to two crossover treatments consuming either carbohydrate and protein hydrolysate (CHO+PRO) or carbohydrate, protein hydrolysate, and additional leucine (CHO+PRO+leu) after completing 30 minutes of standardized physical activity. Primed, continuous infusions of L-[ring-(13)C(6)]phenylalanine and L-[ring-(2)H(2)]tyrosine were administered, and blood and vastus lateralis muscle samples were obtained to evaluate whole-body protein turnover and mixed muscle protein fractional synthetic rate over a 6-hour post-exercise period.
What was found
Mixed muscle fractional synthetic rate averaged 0.081 (SEM 0.003) %/h in CHO+PRO+leu and 0.082 (SEM 0.006) %/h in CHO+PRO, showing no statistically significant difference. Whole-body protein breakdown and synthesis rates did not differ between treatments. Phenylalanine oxidation rates were significantly lower in CHO+PRO+leu versus CHO+PRO. Consequently, whole-body protein balance was significantly higher in CHO+PRO+leu than in CHO+PRO (23.8 (SEM 0.3) versus 23.2 (SEM 0.3) micromol/kg per h; P < 0.05).
Why it matters
Co-ingesting free leucine with post-exercise carbohydrate and protein hydrolysate does not provide an additive stimulus for muscle protein synthesis in older men when ample protein is already provided.
Limits
The trial had a very small sample size of eight participants and was limited to elderly men, excluding women and other age groups. The abstract does not report the exact doses of protein, carbohydrate, or leucine administered, and acute 6-hour tracer measurements cannot determine chronic muscle mass or strength outcomes.
Cited by
- contradicts Combining leucine-rich essential amino acids with whey protein powder makes the whey protein powder more effective at stimulating protein synthesis.