A new study published in the journal Gut has identified a specific type of gut bacteria that may be linked to greater muscle strength. Researchers found that older adults with detectable levels of the bacterium Roseburia inulinivorans had 29% higher handgrip strength compared to those without it.
The study analyzed stool samples from two groups: 90 healthy young adults aged 18 to 25, and 33 older adults aged 65 and up. Researchers then measured physical fitness through handgrip strength tests, leg press and bench press assessments, and VO2 max testing, which measures how efficiently the body uses oxygen during exercise.
Among all the microbes detected, the genus Roseburia, known for producing beneficial short-chain fatty acids, stood out. Specifically, the species Roseburia inulinivorans was consistently linked to stronger muscles. In younger adults, higher levels of this microbe were associated with both stronger grip strength and higher VO2 max. Other species within the same family did not show the same pattern.
To explore whether the bacteria could cause changes in muscle performance, researchers conducted a follow-up experiment in mice. After reducing the animals’ gut microbes with antibiotics, they introduced different Roseburia species into the mice’s microbiomes once a week for eight weeks.
Mice given R. inulinivorans developed about 30% greater grip strength compared to the control group. Their muscles also showed structural changes, including a greater proportion of type II (fast-twitch) muscle fibers, which are responsible for explosive movements like sprinting and lifting. The muscle fibers were also larger overall. Researchers observed shifts in metabolic pathways involved in muscle energy production, suggesting the bacteria may influence how muscle tissue uses fuel.
The findings support the idea of a “gut-muscle axis,” where digestive tract microbes help regulate muscle metabolism and strength. However, researchers caution that the study shows strong associations but does not prove that increasing this bacteria directly boosts strength in humans. Long-term studies are still needed to determine whether higher levels of R. inulinivorans actively improve muscle function or simply reflect other healthy behaviors.
The research reinforces that gut health and physical performance are deeply interconnected. There are already evidence-backed ways to support beneficial gut bacteria that may indirectly benefit muscle health. Roseburia species thrive on fermentable fibers found in foods like oats, beans, lentils, onions, garlic, and asparagus. Resistance training remains the most reliable way to maintain muscle mass and power. A varied diet rich in plants, fermented foods, and whole ingredients helps cultivate a diverse gut microbiome, which is strongly associated with better health outcomes.
Muscle strength has traditionally been viewed through workouts and nutrition. This new research suggests the microbes living in the gut may be another key player. While the findings do not replace the fundamentals of lifting, eating protein, and getting adequate recovery, they add a layer to the conversation. What you feed your gut may be shaping your muscle health at the cellular level long before you notice it in the weight room.
