A groundbreaking study has shed new light on the potential role of gut bacteria in maintaining muscle strength and overall physical function, particularly as we age.

Researchers from the Netherlands and Spain have made a significant discovery involving a species of gut bacteria called Roseburia inulinivorans. This bacterium has been found to be associated with greater muscle strength in humans and improved muscle performance in mice.

The study, published in the journal Gut, involved analyzing stool samples from 90 healthy young adults and 33 older adults. The researchers found that Roseburia inulinivorans was the only genus of bacteria that showed a positive association with both muscle mass and strength.

Among the older participants, those with detectable levels of R. inulinivorans had 29% greater handgrip strength than those in whom the bacterium could not be detected. This difference occurred without a corresponding increase in peak oxygen uptake, indicating better fitness.

Interestingly, individual Roseburia species did not all show the same relationships. While R. faecis and R. intestinalis were not significantly associated with handgrip strength or VO2 max in either age group, R. inulinivorans was found to have a positive association with muscle strength in both young and old adults.

To investigate whether Roseburia might directly influence muscle strength rather than simply being associated with it, the researchers conducted an experiment involving 32 mice. Before the experiment, the mice received a cocktail of antibiotics for two weeks to deplete their gut microbiome. They were then given Roseburia species once a week for 8 weeks.

The results of the mouse experiment were striking. Compared with the control animals, mice receiving R. inulinivorans showed an increase of around 30% in forelimb grip strength, which the researchers used as a measure of muscle function. The improvement was observed after 4, 6, and 8 weeks of treatment.

Mice treated with R. inulinivorans also developed larger muscle fibers and had a significantly greater proportion of type II (‘fast twitch’) fibers in the soleus muscle of the calf compared with the other groups. However, this difference was not significant when the R. inulinivorans mice were compared specifically with those treated with R. intestinalis.

The researchers caution that the study has several limitations. In the mouse experiment, none of the human Roseburia species permanently colonized the animals’ guts. The researchers also did not directly examine certain pathways involving inflammation or neuromuscular signaling, either of which could have contributed to the observed effects.

Despite these uncertainties, the researchers suggest that their findings provide robust evidence supporting a gut-muscle axis in which R. inulinivorans positively modulates muscle metabolism and muscle strength. They conclude that the relative abundance of R. inulinivorans is lower in older adults than in young adults, and its abundance appears to decline with advancing age, a period during which the prevalence of sarcopenia [muscle loss] increases.

The potential implications of this research are significant. If Roseburia inulinivorans can be developed into a probiotic, it could offer a new way to fight age-related muscle loss and preserve muscle strength in older adults.

Key Findings

• Roseburia inulinivorans is associated with greater muscle strength in humans and improved muscle performance in mice.

• The bacterium positively modulates muscle metabolism and muscle strength.

• The relative abundance of R. inulinivorans is lower in older adults than in young adults.