Scientists Found a Gut Bacterium That Seems to Build Muscle Strength

A study published in the journal Gut, led by researchers including teams at Leiden University and the University of Granada, found that a specific gut bacterium, Roseburia inulinivorans, shows up more often in people with stronger muscles. Older adults who had detectable levels of it in their stool samples had, on average, 29% higher handgrip strength than those who didn't, without a matching jump in peak oxygen uptake, meaning the effect looked like real strength, not just better overall fitness.

Handgrip strength isn't just a fun party trick. Doctors use it as a proxy for how well someone is aging, since it correlates strongly with mobility, independence, and even mortality risk in older adults. A bacterium tied that closely to it is a genuinely interesting lead, not just a curiosity.

To test whether the bacterium was actually causing the effect, rather than just showing up alongside it, researchers introduced it directly into mice. The mice given Roseburia inulinivorans saw close to a 30% increase in forelimb grip strength. The researchers believe it works by changing muscle metabolism and converting more muscle fibers into "fast-twitch" type, the kind built for short bursts of power like sprinting or lifting.

This is early-stage research, not a supplement you can buy yet, but it points toward gut bacteria as a real target for treating age-related muscle wasting, a condition that currently has few effective treatments. If a probiotic version of this bacterium eventually proves out in human trials, it could end up mattering a lot more than the study's current small scope suggests.