HMB (Beta-Hydroxy Beta-Methylbutyrate)
HMB is a metabolite of leucine that research suggests may act on both the inhibition of muscle protein breakdown and the promotion of muscle protein synthesis. Evidence supporting its role in preserving lean mass is comparatively stronger in beginners, older adults, and those in a caloric deficit, while results in trained individuals seeking hypertrophy remain mixed across meta-analyses.
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Effects reported in research
Preservation of lean mass during caloric restriction (research reports effects particularly under energy deficit conditions)
Attenuation of muscle protein breakdown (relatively consistent findings reported in beginners and older adults)
Support for muscle protein synthesis (effects suggested especially in populations with insufficient leucine intake)
Reduction in exercise-induced muscle damage and soreness (reported in select RCTs)
Dosage & timing
- The commonly studied dose is 3 g per day, typically divided into three 1 g servings taken throughout the day.
- HMB-FA (free acid form) is reported to be absorbed more rapidly than HMB-Ca (calcium salt form), and timing around training sessions has been explored in research protocols.
Cautions
- •Serious adverse effects at the commonly studied dose of 3 g per day are rarely reported; however, long-term safety data remain limited.
- •Individuals with kidney or liver conditions, as well as those who are pregnant or breastfeeding, should consult a physician before use.
- •Supplements are not a substitute for medical treatment, and consulting a healthcare professional before use is strongly recommended.
Supporting research
Last checked: 2026-06-26