Evidence Level
Moderate
HMB is best understood as an anti-catabolic supplement rather than an anabolic one. It works primarily by reducing muscle protein breakdown, which makes it most valuable in situations of high catabolic stress: untrained individuals experiencing novel training stimulus, caloric restriction, aging, and prolonged bed rest. The Nissen & Sharp (2003) meta-analysis established its efficacy, though subsequent studies in trained athletes have shown more modest benefits. A controversial 2014 study (Wilson et al.) showed dramatic results that have not been replicated and are widely questioned. For trained athletes already consuming adequate protein, the incremental benefit of HMB is small.