 Outpatients with irritable bowel syndrome according to Roma III classification: recurrent abdominal pain or discomfort, at least 3 days per month, in the last 3 months and symptoms begin at least 6 months before diagnosis, associated with 2 or more of: 1 Improvement with defecation, 2 Start associated with changes in the bowel frequency, 3 Start associated with changes in stool consistency. In the absence of alarm symptoms. It will be measured in all patients serology for celiac disease, serum thyroid-stimulating hormone TSH and parasitological test. It will be done, in high suspicion patients, stool culture, breath test for lactose intolerance and breath test for bacterial overgrowth. 