Amino Acids
Evidence: strong_human
HMB is a metabolite of leucine (produced endogenously at ~0.3g/day from typical leucine intake). It reduces proteolysis by inhibiting the ubiquitin-proteasome proteolytic pathway and attenuating caspase-mediated apoptosis in muscle cells. HMB also stimulates muscle protein synthesis via mTOR/p70S6K pathway activation (though less potently than leucine itself) and enhances sarcolemmal membrane integrity by serving as a precursor for de novo cholesterol synthesis in muscle cells (via HMG-CoA). The net effect is anti-catabolic rather than primarily anabolic — it prevents muscle breakdown more than it builds new muscle.
Standard: 3g daily (1g 3x/day)
Maintenance: 3g/day
Administration: oral
Timing: Split into 1g doses with meals (HMB-Ca) or 1-2g 30-60 min pre-exercise (HMB-FA for rapid absorption). Timing matters more for HMB-FA (free acid) than HMB-Ca (calcium salt).
Duration: ongoing during training periods
Most valuable populations: elderly/sarcopenic (preventing muscle loss), injury recovery, caloric deficit (preserving lean mass during cutting), and beginners (accelerating early adaptation). Experienced, well-fed athletes derive less additional benefit. The anti-catabolic mechanism is the key differentiator from other muscle supplements — HMB prevents breakdown rather than primarily stimulating growth. Combination with creatine and vitamin D shows synergistic effects in elderly populations. Cost-effectiveness improves when targeting the populations who benefit most.
HMB-Ca (calcium beta-hydroxy beta-methylbutyrate) is the standard, most-studied form. HMB-FA (free acid form, myHMB Clear) has faster absorption and higher peak levels — better for acute pre-exercise use. Brands: NOW HMB, Optimum Nutrition HMB, TSI Group (myHMB — patent holder).
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