A new study published in the journal Gut has identified a specific type of gut bacteria 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 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 Roseburia genus stood out. This group of bacteria is already known for producing beneficial short-chain fatty acids in the gut. However, only the species Roseburia inulinivorans showed a strong link to muscle strength. Other Roseburia species did not show the same pattern, suggesting different bacteria within the same family may influence muscle health in different ways.
In younger adults, higher levels of R. inulinivorans were linked to both stronger grip strength and higher VO2 max.
To explore whether the bacteria might directly cause changes in muscle performance, researchers ran a follow-up experiment in mice. After reducing the animals’ gut microbes with antibiotics, scientists introduced different Roseburia species into the mice’s microbiomes once per 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. The mice developed a greater proportion of type II, or fast-twitch, muscle fibers, which are responsible for explosive movements like sprinting and jumping. Their muscle fibers were also larger overall.
Researchers also observed shifts in metabolic pathways involved in muscle energy production, suggesting the bacteria may influence how muscle tissue processes fuel. The findings support the idea of a “gut-muscle axis,” where microbes in the digestive tract help regulate muscle metabolism and strength.
What the research means
The research is still early. The study shows strong associations but does not prove that increasing this bacteria directly boosts strength in humans. Long-term studies are needed to determine whether higher levels of R. inulinivorans actively improve muscle function or simply reflect other healthy behaviors that support strength.
Still, the findings reinforce 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. Eating more fiber-rich foods helps feed microbes like Roseburia, which thrive on fermentable fibers found in oats, beans, lentils, onions, garlic, and asparagus. Strength training remains the most reliable way to maintain muscle mass and power, especially with age. A varied diet rich in plants, fermented foods, and whole ingredients helps cultivate a more diverse gut microbiome, which is strongly associated with better health outcomes.
Muscle strength has traditionally been viewed through the lens of workouts and nutrition. This new research suggests another key player may be involved: the microbes living in the gut. The research does not replace the fundamentals of lifting, eating protein, and getting adequate recovery, but it adds a layer to the conversation about how diet and gut health may shape muscle health at the cellular level.
