Nutrition Notes

The Latest on Leucine and Muscle Health

Approximately 40% of total body mass consists of skeletal muscle. Leucine is an essential branched-chain amino acid (BCAA) that has been shown in studies to support muscle structure and support muscle protein synthesis. Unlike other amino acids, leucine and other BCAAs are metabolized mainly in the skeletal muscle. Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of leucine that has also been shown to support muscle structure in the human body.

A recent animal study indicated that HMB supplementation decreased intramuscular fat (IMF) and increased omega-3 polyunsaturated fatty acids and their related metabolites through its ability to modulate lipid metabolism in adipose tissue. Other proposed mechanisms of action involve attenuation of protein degradation and its influence on the mechanistic target of rapamycin/p70S6K pathway, which is involved in the initiation and translation of muscle protein synthesis. HMB may also reduce apoptosis by modulating the mitogen-activated protein kinase/extracellular signal-related kinase and the phosphatidylinositol 3-kinase/protein kinase B (or AKT) pathways. HMB is metabolized to beta-hydroxy-beta-methylglutaryl coenzyme A (HMG-CoA) and may support cellular health and muscle cell stability.

Sarcopenia is most often a result of age-related changes in muscle metabolism and may be associated with decreased protein intake and other changes in nutritional status. A recent systematic review and meta-analysis explored the effect of dietary interventions on age-related muscle atrophy. In this review, it was reported that dietary interventions may be a safe and effective method of supporting muscle health in individuals with limited mobility or a high risk of fall-related injuries, as compared to resistance training. The meta-analysis results indicate that supplementation with HMB can increase muscle mass in older adults.

In one study, supplementation with HMB improved muscle mass in individuals on extended bed rest. In a Norwegian study, which consisted of 417 elderly patients, it was found that self-reported dietary protein intake and postprandial serum plasma concentrations of leucine were lower in individuals with sarcopenia.

Leucine may also support healthy glucose metabolism. Leucine has been shown to have a secretagogue effect on pancreatic beta cells. It may also stimulate the synthesis and secretion of glucagon-like peptide 1, which helps to increase the response to insulin in muscle cells.

Up to 46% of the elderly population does not meet the daily protein intake requirements. Leucine is an essential amino acid, which means that the body does not synthesize it. Studies indicate that dietary sources of leucine or supplementation may support muscle mass, strength, and healthy metabolism. For more information, see this recent review article that contains a comprehensive list of dietary sources of leucine along with a sample meal plan.

By Colleen Ambrose, ND, MAT