Men following plant-rich diets cultivate more beneficial gut bacteria, resulting in increased flatulence and larger stools, according to a rigorous clinical study.
Anyone switching to a plant-based diet has likely noticed more intestinal gas from fruits, vegetables, and legumes. But how much more? Researchers led by Claudia Barber at Spain's Liver and Digestive Diseases Networking Biomedical Research Center (CIBERehd) in Barcelona quantified this in a study published in the journal Nutrients.
The team compared a typical Western diet to a fiber-enriched Mediterranean diet in 20 healthy men aged 18 to 38. Each diet lasted two weeks, following a two-week run-in period. The fiber-rich version emphasized fruits, vegetables, and legumes.
Over the eight-week trial, flatulence doubled in volume and increased sevenfold in frequency on the fiber-enriched diet. Stools were larger (about 200 grams versus 100 grams on the Western diet) with a softer consistency, though daily bowel movement frequency stayed consistent.
These changes align with expectations: more fiber from plants feeds gut microbes.
Species like Anaerostipes hadrus and Agathobaculum butyriciproducens flourished on the plant-rich diet. These bacteria break down fiber into short-chain fatty acids, fueling gas production and retaining more water in stools, as explained by University of New South Wales nutritionist Rosemary Stanton in New Scientist.
Though these effects may feel inconvenient, they're beneficial. Short-chain fatty acids help lower colorectal cancer risk, curb harmful bacteria, and support cardiovascular health. "Our Western notion that farting signals something wrong is misguided. In most cases, it's a marker of a healthy diet and colon," Stanton concludes.
