Effects of Low FODMAP Diet on Colonic Epithelial Physiology in Diarrhea-predominant Irritable Bowel Syndrome

Inclusion Criteria: * Normal serum studies including serum tissue-transglutaminase antibodies, thyroid stimulating hormone levels, C-reactive protein or fecal calprotectin, complete blood count since the onset of symptoms. * Normal stool studies including, ova and parasites since the onset of symptoms * IBS-SSS score of ≥175 at the end of the 7-day screening period In case of presence of any alarm features and/or elevated inflammatory markers (C-reactive protein or fecal calprotectin), patients will be eligible if they have been excluded for inflammatory bowel disease with colonoscopy in the last one year. Exclusion criteria * individuals already on a LFD or other dietary restriction such as gluten free diet within the past 6 months * individuals with any known food allergy or insulin-dependent diabetes * known history of celiac disease, inflammatory bowel disease or microscopic colitis * prior small bowel or colonic surgery or cholecystectomy * pregnant patients * Antibiotics in the past 3 months * Those who regularly use mast cell stabilizers or anti-histaminic or non-steroidal anti-inflammatory agents (NSAIDs) excluding daily baby aspirin or steroids or bile-acid binder.