A Longitudinal Study to Identify IBS Phenotypes Using Fecal Microbiota and Hydrogen Breath Testing

Inclusion Criteria: Adult subjects greater than or equal to 18 years of age who meet Rome IV criteria for diarrhea-predominant irritable bowel syndrome (IBS-D). Prior colonoscopy or sigmoidoscopy within the past 2 years with random colon biopsies to exclude the presence of microscopic colitis. IBS medications, including anti-depressants, will be allowed if the dose has been stable for at least 1 month before inclusion. Medications will be carefully tracked to follow any potential confounding issues. Exclusion Criteria: Underlying celiac disease, inflammatory bowel disease, or other organic disease that could explain their symptoms. Subjects with a history of GI tract surgery, except for cholecystectomy or appendectomy, will also be excluded from the study. Women who are pregnant or breastfeeding Antibiotics taken within 3 months prior to enrollment will not be permitted. Subjects on probiotics must discontinue their use at least 1 month prior to enrollment. Subjects who have previously received formal dietary education for IBS, including a low FODMAP diet, or previously received antibiotics, including rifaximin, for treatment of IBS-D will be excluded from the study.