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HMB (β-Hydroxy β-Methylbutyrate)

Evidence: ★★★☆☆ · Status: OTC Supplement

💡 Did you know? HMB is what your body makes when it breaks down the amino acid leucine — and it's that byproduct, not leucine itself, that carries much of the muscle-sparing signal.

In plain English

It signals "don't break down muscle." Most useful when you're dieting hard, ill, or older — much less impressive in already-trained lifters who eat enough protein.

How it works

Leucine metabolite that stimulates muscle protein synthesis via mTOR and suppresses breakdown via the ubiquitin-proteasome pathway; strongest in catabolic states (caloric deficit, illness, elderly).

Molecular target & official sources

MTOR (NCBI Gene) · HMB (PubChem CID 69362)

Protocol

3 g/day split.

Bottom line

Useful in a deficit or for the elderly; marginal for fed, trained athletes.

Helps with: Build Muscle & Strength

The human evidence

A leucine metabolite that meaningfully helps the untrained, elderly, or catabolic (bed-rest, illness) preserve muscle, but shows little benefit in already-trained lifters who eat enough protein. Match your expectations to your situation.

Stacks with

Adequate protein, creatine and vitamin D; most useful when protein intake is hard to hit.

Shares a pathway — often paired with: Whey / Casein Protein, Rapamycin (Sirolimus), Insulin (anabolic misuse), Ketamine / Esketamine (Spravato).

Availability & where to buy

Available over the counter. Widely available OTC — e.g. iHerb (ships worldwide); in Singapore also Guardian, Watsons, GNC, Shopee / Lazada. Look for a third-party-tested / GMP mark and check the dose per serving. Moderate — ~S$25–40/month; for most trained people, spending on protein and creatine first makes more sense.

How it works: the mTOR pathway →

Used in these protocols

Common questions

Does HMB (β-Hydroxy β-Methylbutyrate) actually work?

Human-evidence rating: 3 of 5. Useful in a deficit or for the elderly; marginal for fed, trained athletes.

How do you take HMB (β-Hydroxy β-Methylbutyrate)?

3 g/day split.

Is HMB (β-Hydroxy β-Methylbutyrate) legal or approved?

Regulatory status: OTC Supplement.