The effects of HMB supplementation during 8 weeks of time-restricted feeding were studied in young, resistance-trained women. Time-restricted feeding is a type of intermittent fasting, where all daily calories are consumed during a smaller “feeding window” each day. Each study participant was assigned to either time-restricted feeding (TRF, 8 hours) or the control group (no feeding time restrictions). Half of the women in the TRF group took three 1g doses of HMB per day (upon waking, mid-morning, and at bedtime), while all other participants took placebo supplements on the same schedule. All of the women completed the same whole-body resistance training program. 24 women completed the entire study as designed. In these women, fat free mass and muscle thickness increased in all three groups. However, only the TRF+HMB group significantly reduced fat mass (-7%) and significantly improved their body composition (-2.3 % body fat, an 8% improvement). These data show that HMB can help reduce body fat while maintaining muscle mass during intermittent fasting in active women.
β-Hydroxy-β-methylbutyrate and its impact on skeletal muscle mass and physical function in clinical practice: a systematic review and meta-analysis.
A systematic review and meta-analysis of fifteen randomized controlled trials was conducted to investigate the efficacy of HMB alone, or supplements containing HMB on skeletal muscle mass and physical function. After reviewing the evidence the authors concluded that HMB and supplements containing HMB increased muscle mass and strength in a variety of clinical conditions.
Pre-exercise beta-hydroxy-beta-methylbutyrate free-acid supplementation improves work capacity recovery: a randomized, double-blinded, placebo-controlled study.
Twenty-three trained men took either a single (3 g) dose of HMB free acid or a placebo 60 minutes before undergoing a single bout of high-intensity exercise. The exercise bout resulted in muscle swelling, decreased jump performance, and decreased force production in both groups, but the participants’ highly trained status allowed for a quick return to normal (within 24 h). However, the single dose of HMB free acid significantly improved recovery of work capacity; the men who took HMB recovered work capacity in just 24 hours, while the placebo group had not yet recovered at 72 hours. Thus, even a single dose of HMB free acid allowed the participants to recover to their full training capacity much sooner after a strenuous, high intensity training session.
In a comprehensive review of HMB studies over the past two decades, the authors examine HMB efficacy. This review also examines why many newer studies, longer in length than some of the original studies and also conducted with HMB in the free acid form, are suggestive of stronger efficacy in both trained and untrained populations. The authors concluded that recent studies utilizing high-intensity training have demonstrated HMB efficacy in maintaining muscle mass and attenuating the inflammatory response. In particular these studies show improved efficacy of HMB free acid in trained athletes.