1.
Supplementation with the Leucine Metabolite β-hydroxy-β-methylbutyrate (HMB) does not Improve Resistance Exercise-Induced Changes in Body Composition or Strength in Young Subjects: A Systematic Review and Meta-Analysis.
Jakubowski, JS, Nunes, EA, Teixeira, FJ, Vescio, V, Morton, RW, Banfield, L, Phillips, SM
Nutrients. 2020;(5)
Abstract
β-hydroxy-β-methylbutyrate (HMB) is a leucine metabolite that is purported to increase fat-free mass (FFM) gain and performance in response to resistance exercise training (RET). The aim of this systematic review and meta-analysis was to determine the efficacy of HMB supplementation in augmenting FFM and strength gains during RET in young adults. Outcomes investigated were: total body mass (TBM), FFM, fat mass (FM), total single repetition maximum (1RM), bench press (BP) 1RM, and lower body (LwB) 1RM. Databases consulted were: Medical Literature Analysis and Retrieval System Online (Medline), Excerpta Medica database (Embase), The Cumulative Index to Nursing and Allied Health Literature (CINAHL), and SportDiscus. Fourteen studies fit the inclusion criteria; however, 11 were analyzed after data extraction and funnel plot analysis exclusion. A total of 302 participants (18-45 y) were included in body mass and composition analysis, and 248 were included in the strength analysis. A significant effect was found on TBM. However, there were no significant effects for FFM, FM, or strength outcomes. We conclude that HMB produces a small effect on TBM gain, but this effect does not translate into significantly greater increases in FFM, strength or decreases in FM during periods of RET. Our findings do not support the use of HMB aiming at improvement of body composition or strength with RET.
2.
The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: a systematic review and meta-analysis.
Xu, ZR, Tan, ZJ, Zhang, Q, Gui, QF, Yang, YM
The British journal of nutrition. 2015;(1):25-34
Abstract
In the present study, we performed a meta-analysis to assess the ability of leucine supplementation to increase the muscle protein fraction synthetic rate and to augment lean body mass or leg lean mass in elderly patients. A literature search was conducted on Medline, Cochrane, EMBASE and Google Scholar databases up to 31 December 2013 for clinical trials that investigated the administration of leucine as a nutrient that affects muscle protein metabolism and muscle mass in elderly subjects. The included studies were randomised controlled trials. The primary outcome for the meta-analysis was the protein fractional synthetic rate. Secondary outcomes included lean body mass and leg lean mass. A total of nine studies were included in the meta-analysis. The results showed that the muscle protein fractional synthetic rate after intervention significantly increased in the leucine group compared with the control group (pooled standardised difference in mean changes 1·08, 95% CI 0·50, 1·67; P< 0·001). No difference was found between the groups in relation to lean body mass (pooled standardised difference in mean changes 0·18, 95% CI - 0·18, 0·54; P= 0·318) or leg lean mass (pooled standardised difference in mean changes 0·006, 95% CI - 0·32, 0·44; P= 0·756). These findings suggest that leucine supplementation is useful to address the age-related decline in muscle mass in elderly individuals, as it increases the muscle protein fractional synthetic rate.