Outcome
    Limited

    HMB for Protein Metabolism

    HMB reduces protein breakdown mainly in catabolic states, not in well-fed trained people.

    Overview

    HMB reduces protein breakdown mainly in catabolic states, not in well-fed trained people.

    Verdict

    Insufficient evidence

    How It Works

    A leucine metabolite that downregulates ubiquitin-proteasome mediated proteolysis.

    Dosing & Protocol

    Typical dose

    Recommended dose
    3g/day split
    Expected timeframe
    4-8 weeks

    Protocol

    form
    Not applicable
    duration
    Not applicable
    co factor
    Evidence is insufficient for protein metabolism as a meaningful endpoint. The underlying mechanism is real and reasonably well characterised: HMB, a metabolite of leucine, attenuates muscle protein breakdown by downregulating the ubiquitin-proteasome pathway, and stable isotope studies at 3 g/day show reduced proteolysis. It has a weaker effect on protein synthesis than leucine itself. The problem is translation - reduced breakdown produces measurable functional benefit mainly where breakdown is elevated, in older adults, bed rest and catabolic illness, and not in trained, well-fed people. Adequate dietary protein of 1.6-2.2 g/kg/day spread across meals influences net protein balance far more than HMB does.
    titration
    Not applicable
    starting dose
    Not applicable - protein metabolism is a mechanism, not an outcome you can act on

    Evidence

    What the studies say

    Effects are meaningful in bed rest, illness and severe caloric restriction. Well-controlled trials in trained athletes with adequate protein show little to no benefit.

    Leucine supplementation and muscle protein synthesis in older adults: a systematic review and meta-analysis

    Score: 7/10
    2015
    meta_analysis
    n=999

    Xu ZR, Tan ZJ, Zhang Q +2 more

    Leucine significantly increased muscle protein synthesis rate but did not consistently increase lean body mass

    View source

    Safety

    Caveats

    Redundant when protein intake is adequate.

    Less likely to help if

    Well-fed individuals with adequate protein intake, in whom protein breakdown is not the limiting factor.

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    Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.