Efficacy of L-leucine Supplementation Coupled With Resistance Training in Untrained Midlife Women.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 31577520 · doi:10.1080/07315724.2019.1650675
What was done
Thirty-six untrained peri- and postmenopausal women were randomized to receive either 5 g of L-leucine or a placebo daily while undergoing a 10-week resistance training program performed three times per week. Before and after the intervention, researchers evaluated body composition (fat-free mass), muscle strength, and circulating hormone levels (estradiol, testosterone, insulin-like growth factor-1, growth hormone, and cortisol).
What was found
The abstract reports no exact numerical data or effect sizes. Both the leucine and placebo groups demonstrated significant increases in muscle strength following resistance training. However, there were no significant differences between the groups for strength gains, fat-free mass, or any of the measured serum hormone concentrations.
Why it matters
Leucine is widely promoted to stimulate muscle protein synthesis, but these findings suggest that supplemental leucine provides no additional benefit for muscle mass, strength, or anabolic hormonal milieu over resistance training alone in untrained midlife women.
Limits
The sample size was small (n = 36) and the abstract lacks numerical data, baseline dietary protein intake information, and specific compliance rates. The study evaluated only a single dosage (5 g/day) over a relatively short duration (10 weeks), and findings may not generalize to athletic populations, older adults with clinical sarcopenia, or men.
Cited by
- contradicts Postmenopausal women require at least double the premenopausal amount of dietary leucine to trigger muscle protein synthesis.