Though the cause of IBS-C is still unknown, research suggests that multiple factors — such as the gut-brain axis, abnormal muscular contractions, gut microbes, hormones, and genetics — could play a role in the disease. IBS is twice as common in women compared to men, which could be explained, in part, by hormonal changes during the menstrual cycle.[1][2]
Some studies have found a higher prevalence of methane-positive small-intestinal bacterial overgrowth (SIBO) in people with IBS-C and other forms of constipation, suggesting that this form of SIBO could be linked to symptoms via excess methane production (which could slow intestinal transit.) However, it’s unclear whether methane production is a cause or consequence of slow transit.[3]