Does HMB improve protein balance in muscles?
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The Impact of HMB on Muscle Protein Balance
Introduction to HMB and Muscle Protein Balance
Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the essential amino acid leucine, known for its potential to enhance muscle protein synthesis and reduce muscle protein breakdown. This article synthesizes findings from multiple studies to determine whether HMB improves protein balance in muscles.
HMB and Muscle Protein Synthesis
Effects in Fasting Conditions
Research indicates that HMB can significantly improve muscle protein balance during catabolic conditions such as fasting. A study comparing leucine-rich whey protein, soy protein, and soy protein with HMB supplementation found that HMB notably improved net protein balance in muscles during a 36-hour fasting period. This improvement was associated with increased phosphorylation of key proteins in the mTOR pathway, which is crucial for muscle protein synthesis.
Impact on Older Adults
In older adults, HMB supplementation combined with resistance exercise training (RET) has shown promising results. A study involving older men demonstrated that HMB-FA supplementation increased muscle protein synthesis (MPS) in the trained legs during the initial weeks of RET. Although there were no significant differences in muscle strength or mass between the HMB and placebo groups, the HMB group exhibited a significant increase in thigh lean mass.
Animal Studies
Animal studies further support the anabolic effects of HMB. In growing pigs fed low-protein diets, HMB supplementation stimulated positive protein balance in muscles, particularly those with oxidative fiber types. This effect was linked to the activation of the Akt signaling pathway, which plays a role in muscle growth and protein synthesis.
HMB and Muscle Protein Breakdown
Critically Ill Patients
In critically ill patients, HMB supplementation has been shown to reduce net protein breakdown. A randomized controlled trial found that while HMB did not significantly reduce muscle wasting over a 10-day period, it did improve amino acid metabolism and reduce net protein breakdown, leading to better overall health outcomes.
Diabetes-Induced Muscle Wasting
In a study on rats with streptozotocin-induced diabetes, HMB administration adjusted branched-chain amino acid concentrations in plasma and muscles, which can be considered beneficial. However, the effects on muscle weight and protein content were not significant, indicating that HMB's impact on muscle protein balance may vary depending on the underlying health condition.
HMB and Physical Performance
Pre-Frail Older Adults
A 12-week study on pre-frail older adults found that high-protein oral nutrition shakes supplemented with HMB significantly increased muscle mass and improved physical performance. The study also noted a reduction in intramuscular adiposity, suggesting that HMB can enhance muscle quality in addition to quantity.
Meta-Analysis Findings
A systematic review and meta-analysis of randomized controlled trials concluded that HMB supplementation, either alone or in combination with other nutrients, increased muscle mass and strength across various clinical conditions. However, the effect sizes were small, and the studies varied in quality, indicating a need for further high-quality research.
Conclusion
Overall, the evidence suggests that HMB can improve muscle protein balance by enhancing muscle protein synthesis and reducing protein breakdown, particularly in catabolic conditions and older adults. While the effects on muscle mass and strength are generally positive, they are modest and may vary depending on the population and health status. Further research is needed to fully understand the long-term benefits and optimal conditions for HMB supplementation.
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