One possible contributor to irritable bowel syndrome (IBS) is bacterial overgrowth in the small intestine. Research appearing in the Journal of the American Medical Association (2004;292(7):852-858) suggests this may be the case. Bloating that occurs soon after eating is often considered a clinical clue pointing toward small intestinal bacterial overgrowth (SIBO).
Hydrogen excretion after ingesting lactulose (a non-absorbable sugar) is found in approximately 84% of individuals with IBS. This breath test is an indirect way to assess bacterial overgrowth in the small intestine, as no reliable direct testing method is currently available. When bacterial overgrowth is addressed, symptoms reportedly improve in about 75% of patients with IBS.
Additional research published in the American Journal of Gastroenterology (December 2000;95(12):3503-3506) evaluated patients with IBS and found that reducing bacterial overgrowth in the small intestine led to symptom improvement in roughly half of the participants.
The intestinal tract functions as a complex ecosystem and contains several pounds of bacteria. Under normal conditions, most bacteria are confined to the large intestine. Many bacterial species play beneficial roles, including protecting the intestinal lining, assisting with detoxification, producing certain vitamins, and helping to keep potentially harmful organisms in balance. Probiotics are commonly used to help support healthy intestinal flora. Research appearing in the American Journal of Gastroenterology (2000; 95(5):1231-8)demonstrated that probiotic supplementation may reduce symptoms in some individuals with IBS.
Taken together, these studies suggest that intestinal bacteria may play a role in IBS. Viewing the intestinal tract as an ecosystem may help frame supportive strategies aimed at improving gut balance and symptom patterns.
