Gut Bacteria Linked to Muscle Strength in Older Adults

Grip strength is often an overlooked indicator of overall health, but its decline can signal broader physical deterioration in older adults, increasing the risk of falls, loss of independence, and sarcopenia – the age-related loss of muscle mass, and strength. Recent research suggests a surprising connection between the intestinal microbiome and muscle strength, offering a potential recent avenue for maintaining physical function as we age.

The Role of Roseburia inulinivorans

Researchers at the University of Almería, the University of Granada, and the Leiden University Medical Centre in the Netherlands have identified Roseburia inulinivorans, a species of intestinal bacteria, as being associated with increased muscle strength in both young and older adults. Studies show that older adults tend to have lower populations of this bacterium compared to their younger counterparts. [1]

Experiments using mice demonstrated that R. Inulinivorans directly increases grip strength and alters the physical structure of muscle cells. These findings, published in the journal Gut, support the concept of a gut–muscle axis, where gut bacteria communicate with skeletal muscle and influence its function and deterioration. [1]

Study Details: Comparing Young and Older Adults

The research team analyzed stool samples from 90 healthy young adults (18–25 years) and 33 older adults (65 years or older). Participants underwent physical fitness tests to measure grip strength, leg press strength, bench press strength, and cardiorespiratory fitness. [1]

While several Roseburia species were present in both groups, R. Inulinivorans consistently correlated positively with muscle strength. Older adults positive for this bacterium exhibited approximately 29 percent greater hand grip strength than those who tested negative. In younger adults, higher levels of R. Inulinivorans were associated with both greater grip strength and improved cardiorespiratory fitness. [1]

Mouse Model Experiments Confirm Findings

To establish a causal link, researchers conducted experiments with mice. After eliminating their gut bacteria with antibiotics, 32 male mice received weekly doses of selected Roseburia species for eight weeks, while a control group received sterile saline. Only R. Inulinivorans significantly increased grip strength in the treated mice – by approximately 30 percent – compared to the control group. [2]

mice treated with R. Inulinivorans developed larger muscle fibers in their calf muscles and a higher concentration of fast-twitch type II fibers, which are associated with strength and power. [2]

Transient Effects and Metabolic Pathways

Interestingly, Roseburia species did not permanently colonize the mice’s intestines. This suggests that the muscle-strengthening effect is likely due to transient microbial signaling or metabolites rather than long-term gut colonization. Researchers observed increased activity in the purine and pentose phosphate pathways – essential for energy production and cell repair – in mice treated with R. Inulinivorans. Similar pathway patterns were also observed in young adults with higher concentrations of the bacterium in their gut microbiomes. [2]

Age-Related Decline and the Gut-Muscle Connection

The study also revealed an age-related decrease in R. Inulinivorans. While significantly lower in older adults (65+) compared to younger adults (18–25) within the study cohorts, a broader meta-analysis of over 3,500 individuals showed only a slight, non-significant difference. Researchers also noted decreased levels of the bacterium in individuals with sarcopenia and muscle-wasting conditions like cachexia. [1]

The gut–microbiome–muscle axis appears to be bidirectional. Research suggests that strength training can increase the abundance of Roseburia by an average of two percent, potentially creating a feedback loop where exercise promotes beneficial gut bacteria, which in turn support muscle function. [1]

Future Directions and Potential Applications

Researchers are exploring probiotic supplementation as a potential strategy to prevent or mitigate age-related muscle loss. Human intervention trials are planned to determine the optimal dosage and duration of R. Inulinivorans supplementation needed to achieve measurable results. Understanding the mechanisms by which R. Inulinivorans influences amino acid metabolism and muscle-related pathways will be crucial for future research. [1]