HMB

Preliminary· human data

Also known as: β-Hydroxy β-methylbutyrate

A leucine metabolite with a plausible anti-catabolic role but oversold muscle claims.

What it is

HMB (beta-hydroxy beta-methylbutyrate) is a metabolite of the amino acid leucine, which you already get from protein. It is marketed for muscle growth and reduced muscle breakdown.

What the evidence shows

Muscle growth in trained lifters. Marketing claim· human data In well-fed, trained people, better-controlled studies have struggled to reproduce the dramatic early results, and the overall picture is underwhelming.

Anti-catabolic role in specific situations. Preliminary· human data Its more plausible use is reducing muscle breakdown during heavy dieting, injury, or in older or untrained people — not adding slabs of muscle to a healthy trainee.

Who it suits

There may be a niche during aggressive fat-loss phases or for those returning from a lay-off, but for most trained lifters eating enough protein it adds little.

Practical notes

If your protein intake is adequate, you already produce some HMB, which is one reason supplementing often does nothing noticeable. Prioritise total protein and training first — see the macro calculator — and treat HMB as a low-priority extra rather than a core supplement.

Sources

Frequently asked questions

Does HMB build muscle?
The evidence is mixed and mostly underwhelming in trained lifters who already eat enough protein. Its more plausible role is anti-catabolic — reducing muscle breakdown — which may matter most during heavy dieting, injury or in older or untrained people, not for adding slabs of muscle.
Isn't it just from protein anyway?
HMB is a metabolite of the amino acid leucine, which you already get from protein. If your protein intake is adequate, you're producing some HMB already, which is one reason supplementing often adds little.
Why the gap between studies and marketing?
A handful of early studies showed dramatic results that later, better-controlled research struggled to reproduce. The marketing tends to lean on the optimistic early data rather than the more sober overall picture.

Related supplements

Written and reviewed by Mathew Beale — MSc Biotechnology, University of Reading.

Last reviewed: