Abstract
β-hydroxy-β-methylbutyrate (HMB) is a leucine metabolite used as a nutritional supplement purported to increase lean body mass and performance in response to resistance exercise training (RET). However, literature definitive evidence-based answer to the question of the efficacy of HMB is lacking. PURPOSE: The aim of this systematic-review and meta-analysis was to determine the efficacy of HMB supplementation, in the calcium (HMB-Ca) or free acid (HMB-FA) form, to augment lean body mass and strength gains during RET. METHODS: A systematic search on Medline, Embase, CINAHL and SportDiscus, from 1996-Oct 2019 was conducted. Inclusion criteria for studies were: randomized controlled trial (RCT), RET ≥ 3 weeks (training sessions at least 2 x/week), male subjects <50 y, and ingesting 3g/d of HMB-Ca or HMB-FA with or without protein or amino acids. Random-effects meta-analysis was performed in Review Manager V.5.3. Cochrane risk-of-bias tool for randomized trials (RoB 2) was applied. Studies with 3 domains judged as unknown risk or at least 1 domain judged as high risk of bias were excluded from the analysis. Industry-related sponsorship or authorship were considered high risk of bias. The following outcomes were investigated: total body mass (TBM), lean body mass (LBM), fat mass (FM), total 1 repetition maximum (RM), bench press (BP) 1RM, and lower body (LwB) 1RM. RESULTS: Fourteen studies fit the inclusion criteria. However, after removing studies according to RoB2 scoring, the number of analysed studies dropped to seven. A total of 291 male participants (18-45y) were included, and the mean study duration was 8 ± 3 weeks with a training frequency of 2-5 d/week. No significant effects were found on TBM (0.34kg [-0.09, 0.77], p=0.12), body composition (LBM: -0.06kg [-0.55, 0.42], p=0.80; FM: 0.11kg [-0.12, 0.34], p=0.34) or strength (total 1RM: 1.30kg [-3.12, 5.72], p=0.56; BP 1RM: 1.49kg [-1.33, 4.30], p=0.30 and LwB 1RM: 3.96kg [-1.09, 9.02], p=0.12). CONCLUSION: This meta-analysis showed that HMB does not improve changes in body mass and composition caused by RET. In addition, effects on strength were not significant. Therefore, the claims for HMB consumption to optimize RET effects seem to be based on studies with considerable risk of bias. When such studies are not considered, there is no support for HMB ingestion.
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