Ruminococcus Bromii

Ruminococcus bromii (R. bromii) is an anaerobic bacterium that lives in the human colon and is considered a keystone organism for its unique ability to break down resistant starch, which is the fraction of dietary starch that escapes digestion in the small intestine. Resistant starch passes into the large intestine intact. Most gut bacteria cannot initiate its breakdown because it remains packaged inside dense granules. R. bromii possesses specialized enzymes and adherence structures that allow it to open up these granules and release simpler carbohydrates that it and other microbes can then metabolize.

Once resistant starch is unlocked, other beneficial species, particularly butyrate-producing bacteria such as Faecalibacterium and Roseburia, can thrive. Butyrate is a short-chain fatty acid that serves as the primary fuel for colon cells, reinforces the gut barrier, lowers inflammation, and contributes to metabolic resilience. Because R. bromii controls access to resistant starch, people with low levels often show poor fermentation of these fibers despite adequate dietary intake. Those with higher levels typically generate more butyrate when eating resistant starch-rich foods.

R. bromii has been linked to several aspects of health. Individuals with greater abundance tend to have better glycemic responses to resistant starch and may show improved post-meal glucose control. Its presence is also associated with healthier body weight and more favorable metabolic markers. Lower R. bromii levels appear in people with obesity, cardiovascular risk, and chronic kidney disease, though these are associations rather than proof of causation. Its abundance also differs between individuals with and without certain immune and mood-related conditions, suggesting possible roles in immune regulation and gut–brain communication, although mechanisms remain under investigation.

Diet is the primary way to influence R. bromii. Resistant starch-rich foods such as cooked-and-cooled potatoes, legumes, certain whole grains, unripe bananas, and targeted prebiotic blends can increase its abundance. Fibers like galacto-oligosaccharides may also support its growth. Conversely, some plant compounds such as berberine can modify its activity, including its interaction with bile acids, which may contribute to berberine’s metabolic effects.