Irritable bowel syndrome (IBS) affects an estimated 11–14% of Americans and may involve small intestinal bacterial overgrowth (SIBO) in a substantial subset of patients.
Research published in the Journal of the American Medical Association (August 18, 2004;292(7):852–858) found that the lactulose breath test, a marker of bacterial overgrowth in the small intestine, was abnormal in 84% of patients with IBS. When bacterial overgrowth was treated, approximately 75% of patients experienced symptom improvement.
Supporting this, a study in the American Journal of Gastroenterology (December 2000;95(12):3503–3506) evaluated 202 patients with IBS. Based on lactulose hydrogen breath testing, 157 patients had evidence of bacterial overgrowth, while 45 did not. Patients with bacterial overgrowth were treated with antibiotics. At follow-up, 48% of those whose bacterial overgrowth resolved no longer met diagnostic criteria for IBS, while patients whose breath tests remained abnormal did not experience symptom improvement.
Together, these findings support a meaningful link between SIBO and IBS, while also underscoring that IBS is heterogeneous—not all patients have bacterial overgrowth, and not all respond to the same intervention.
