Even among healthy adults, skeletal muscle mass decreases by as much as two percent each year after the age of 50. This age-related muscle loss is correlated with a decline in the physical function and activity of daily living.
To date, researchers have not yet identified an effective means to reverse or even prevent muscle loss. While resistance training offers the most promise, this is not feasible for all older adults. In particular, exercise cannot be recommended for those with limited mobility or those who are at high risk for a fall-related injury. As such, effective dietary interventions are needed.
With this in mind, the UA researchers looked at oral amino acid supplementation as one such dietary intervention to address muscle mass loss among older adults.
HMB is an active metabolite of the amino acid, leucine. Studies show that it may improve muscle protein turnover by activating the mammalian target of rapamycin in cell signaling pathways. Some reports also suggest that HMB may decrease muscle protein breakdown by reducing inflammation.
Meanwhile, the amino acid arginine has been shown to work synergistically with HMB to reduce oxidative stress and inflammation, helping attenuate muscle loss.
Finally, glutamine is the most abundant free amino acid in the body. Studies on glutamine show that it can upregulate muscle protein synthesis. In addition, its antioxidant and immunomodulatory properties may also complement HMB and arginine.
For their study, the researchers sampled 31 community-dwelling men and women between the ages of 65 and 89.
These participants were randomly assigned to one of two groups. One group received oral doses of the amino acid supplements twice a day every day for six months. This amounted to 3 g HMB, 14 g arginine and 14 g glutamine every day for each participant in this group.
The second group received a placebo.
The lean body mass of all the participants was measured at the start and at the end of the study. To do this, the researchers used a combination of air displacement plethysmography, dual-energy x-ray absorptiometry (DXA) and the four-compartment model. Muscle volume, on the other hand, was measured using magnetic resonance imaging (MRI).
In addition, the participants also performed a battery of tests to assess physical function. The tests were selected to represent typical activities of daily living. They included an eight-foot up-and-go test, a 25-foot walk test and a timed stair climb.
Following the study, the researcher noted that the group that took the supplements demonstrated an improvement in total lean body mass. Regional analysis using DXA found an improvement in arm lean mass within the treatment group. MRI analysis, however, did not find any significant improvements in quadriceps volume for either group.
The treatment group also exhibited improved physical performance in the test. In particular, the researchers noted that they exhibited a marked improvement in the timed stair climb compared to the control group. (Related: Boost your athletic performance with this proven amino acid.)
Based on these findings, the researchers concluded that dietary supplementation with HMB, arginine and glutamine can improve total body lean mass among a small sample of healthy adults. That said, they also stated that further study is needed to better understand why this is the case as well as to determine whether this kind of supplementation can also benefit frail elders.
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