Study under review: β-Hydroxy-β-methylbutyrate and its impact on skeletal muscle mass and physical function in clinical practice: a systematic review and meta-analysis.
Muscle loss is one of the comorbidities associated with aging and wasting diseases, such as cancer cachexia (wasting syndrome characterized by weight loss, anorexia, weakness, low energy, and anemia), HIV, and critical illness. Loss of muscle mass and, as a byproduct, lower strength, is associated with reduced physical activity, increased risk of metabolic diseases, and increased frailty. Exercise, specifically resistance training, is a robust intervention for attenuating muscle loss. However, as exercise is not always a viable option for some people, pharmaceutical and/or nutraceutical approaches aimed at attenuating muscle mass loss warrant investigation.
Muscle tissue is constantly in turnover, with muscle tissue being built (anabolism) and broken down (catabolism). Muscle loss occurs when catabolism exceeds anabolism. There are specific molecules that can trigger anabolism and/or decrease catabolism in muscle. These molecules would make ideal interventions for addressing muscle loss among populations of people for whom exercise may not be an option or who may need additional therapeutic approaches.
β-Hydroxy-β-methylbutyrate (HMB) may be one such molecule. It’s a metabolite of the amino acid leucine and displays both anabolic and anti-catabolic properties. As you can see in Figure 1, HMB activates classic protein synthesis (muscle growth) pathways, such as mTOR. Furthermore, it has been shown to attenuate proteolysis processes in muscle tissue, such as proteolysis-inducing factor.
There have been several randomized controlled trials examining the effect of HMB on muscle mass and strength in a variety of populations at risk for muscle loss. However, the results vary across conditions and method of assessment. For example, one study showed that HMB led to an increase in fat free mass and strength in individuals with bronchiectasis, a condition characterized by thickened bronchi from inflammation and infection. Conversely, another study found that HMB did not affect muscle mass, strength, or physical function. Currently, no meta-analyses have been conducted to harmonize disparate findings like these in order to examine the effect of HMB on muscle mass, strength, or physical function among people with various medical conditions that can promote or trigger muscle wasting.
The study under review was a systematic review and meta-analysis investigating the effects of HMB, either alone or in conjunction with other supplements, on skeletal muscle mass and physical function and strength during critical illness and clinical patient populations.
Muscle wasting is one of the key comorbidities associated with aging and diseases of wasting. In pertinent populations, HMB has shown promise for mitigating the loss of muscle mass and strength in some randomized controlled trials. The present study was a meta-analysis aimed at harmonizing the results across randomized controlled trials and assessing the effect of HMB on muscle mass and strength in a variety of ill populations at risk for muscle loss.
Other Articles in Issue #57 (July 2019)
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Mini: The American Diabetes Association’s consensus report on nutrition therapy for adults with diabetes and prediabetes
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Citrulline is a non-essential amino acid that could boost performance in theory. But does it do so in fact? Here, we review a recent meta-analysis examining this question.
Beyond connective tissue: investigating collagen supplementation for strength and muscle mass
Getting enough protein is an essential part of gaining muscle mass. However, not all protein's created equal. This RCT aimed to explore whether collagen supplementation can help bulk up.
Foods engineered to be cheap and tasty might make you eat more
There is a strong association between eating processed foods and gaining weight. This RCT took great pains to determine whether or not the link is actually causal.