HMB

Supplements · Sports Performance · Supplement, Typed Supps

A by-product of an amino acid, studied for slowing muscle breakdown.

Stage by stage

Intake (Capsule or powder): Absorbed efficiently in the small intestine.
Small intestine (Efficient absorption): Absorbed alongside standard digestion.
Bloodstream (Carried to muscle): Carried in the blood to muscle tissue.
Muscle protein breakdown (Reduces breakdown): Studied for a possible role in reducing muscle protein breakdown during intense training or limited food intake.

What the evidence supports

Preserving muscle during illness, bed rest, or severe calorie restriction — moderate evidence. The most defensible use — reducing muscle loss in catabolic states, including in older hospitalised adults.
Increasing muscle or strength in trained lifters — insufficient evidence. Early results claiming large effects came from a small number of linked research groups and have not replicated. Independent trials in trained people find little or nothing.
Helping untrained people starting a programme — limited evidence. Some effect in beginners, which is also the population where almost anything looks effective.

Typical dose

3 g daily, usually as 1 g with each of three meals

Upper limit: No formal UL. Across nine studies at 3 g daily for three to eight weeks there were no adverse changes in blood chemistry, haematology, or markers of kidney and liver function; up to 6 g daily for eight weeks has been examined similarly

Timing

With food, standard dosing.

Time to effect

Weeks: Consistent use for any reported effect on muscle recovery in studies.

Medication interactions

No established drug interactions: HMB is a metabolite of leucine and nothing clinically important has been documented. Read that as a thin literature rather than a clean bill of health — the safety studies were short, in mostly healthy people, and were not designed to find interactions. (moderate)
Statins and blood-pressure medication: In the pooled safety data HMB slightly lowered total and LDL cholesterol and systolic blood pressure. The changes are small and the overlap is theoretical rather than reported, but if you are being titrated on either drug it is worth mentioning. (moderate)

Common myth

“HMB works as well as anabolic steroids.” In reality: Its studied effects are modest and mostly relevant in specific contexts, like reducing muscle loss — not comparable to anabolic substances.