✔ Evidence-Based. Scientifically Reviewed by Michael Sharpe, MSc.
The dynamic equilibrium (protein breakdown and synthesis) in protein turnover is required for the maintenance of skeletal muscle mass.
The single amino acid leucine has the most distinct anabolic properties of all nutrients when it comes to functioning as a trigger factor for the commencement of protein synthesis.
Leucine is a branched-chain amino acid (BCAA) that may be catabolized inside muscle, raising the potential that its metabolites are involved in mediating the anabolic effects.
It is theorised that one of the metabolites of leucine, known as HMB (β-Hydroxy β-methylbutyric acid), may also possess anabolic or anti-catabolic activity.
Let's explore one study on the effects of leucine and HMB on muscle protein synthesis and breakdown.
HMB & Leucine Study
The goal of one study was to see how leucine and its metabolite HMB affected muscle protein anabolism. They investigated the impact of HMB or leucine alone on muscle protein synthesis and muscle proteolysis.
Orally taken 3.42 g free-acid HMB (providing 2.42 g of pure HMB) had quick absorption in the plasma and muscle, and increased muscle protein synthesis by about 70%.
3.42g of leucine also increased muscle protein synthesis by about 110%.
While both HMB and leucine boosted anabolic signalling (via mTOR), leucines effect was stronger and lasted for longer (p70S6K1 signalling lasted 90 min vs 30 min for HMB).
In an insulin-independent way, HMB ingestion reduced muscle protein breakdown by about 57%.
Conclusion
The researchers conclude that exogenous HMB causes acute muscle anabolism (via increased muscle protein synthesis and decreased muscle protein breakdown), but it done this via a mechanism different from (and/or supplementary) to leucine.
Because HMB and leucine worked in a different way, there may be a synergy of taking a HMB and leucine supplement together.
Further Reading
References
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This evidence based analysis of the effect of HMB and leucine on muscle anabolism features 1 reference, listed below.
1. Wilkinson DJ, Hossain T, Hill DS, Phillips BE, Crossland H, Williams J, Loughna P, Churchward-Venne TA, Breen L, Phillips SM, Etheridge T, Rathmacher JA, Smith K, Szewczyk NJ, Atherton PJ. Effects of leucine and its metabolite β-hydroxy-β-methylbutyrate on human skeletal muscle protein metabolism. J Physiol. (2013, Jun 1) ✔
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