In recent years, researchers have demonstrated that the microbiome of the gut is influential over the pace of aging. Dietary changes, immune system changes, tissue changes, and microbiome population changes all take place and interact with one another with advancing age. There is evidence for changes in the microbiome to aggravate the immune system into chronic inflammation, and evidence for declining immune function to lead to unhelpful changes in the balance of microbes. Some people have better microbiomes, such as athletes tending to have microbes that secrete compounds such as proprionate that can incrementally improve health. In animal models, transplanting gut microbes from young to old animals improves the health and longevity of the older animals.
In this broader context, we should probably expect fitter adults to have a measurably different gut microbiome in comparison to their less fit and overweight peers. Are those different bacteria helping to maintain fitness? The evidence here suggests that they are, but questions of causation remain: is it diet, weight, and inflammation that determines whether or not helpful bacteria are present, or do natural variations in bacterial populations between individuals make it easier or harder to maintain fitness?
The gut-muscle axis, or the relationship between gut microbiota and muscle mass and physical function, has gained momentum as a research topic in the last few years as studies have established that gut microbiota influences many aspects of health. While researchers have begun exploring the connection between the gut microbiome, muscle, and physical function in mice and younger adults, few studies have been conducted with older adults. To gain insight into this population, the researchers compared bacteria from the gut microbiomes of 18 older adults with high-physical function and a favorable body composition (higher percentage of lean mass, lower percentage of fat mass) with 11 older adults with low-physical function and a less favorable body composition. The small study identified differences in the bacterial profiles between the two groups.
Similar bacterial differences were present when mice were colonized with fecal samples from the two human groups, and grip strength was increased in mice colonized with samples from the high-functioning older adults, suggesting a role for the gut microbiome in mechanisms related to muscle strength in older adults. Specifically, when compared to the low-functioning older adult group, the researchers found higher levels of Prevotellaceae, Prevotella, Barnesiella, and Barnesiella intestinihominis - all potentially good bacteria - in the high-functioning older adults and in the mice that were colonized with fecal samples from the high-functioning older adults.
"While we were surprised that we didn't identify a role for the gut microbiome on the maintenance of body composition, with these results we now start to understand the role of gut bacteria in the maintenance of muscle strength in older adults. For example, if we were to conduct an intervention to increase Prevotella levels in the gut microbiome, we would expect to see an increase in muscle strength if these bacteria are involved. Prevotella's role in the maintenance of muscle strength in older adults is one area we expect to continue to explore."