Inclusion Criteria:  Patients with diarrhea-predominant post-infectious IBSand patients with diarrhea predominant classical IBS (non PI-IBS) who will be used as controls  Diagnosis of IBS will be made according to the ROME iV criteria as following:  Recurrent abdominal pain, on average, at least 1 day/week in the last 3 months, associated with two or more of the following criteria:  Related to defecation Associated with a change in frequency of stool Associated with a change in form (appearance) of stool. The above-mentioned criteria have to be fulfilled for the last 3 months with symptom onset at least 6 months before diagnosis.  Diagnosis of post infectious IBS will be made according to the Rome Foundation Working Team criteria as following:  Recurrent abdominal pain, on average, at least 1 day per week in the last 3 months, with symptom onset at least 6 months before diagnosis, associated with two of the following:  defecation a change in frequency of stool a change in form (appearance) of stool Symptom development immediately after resolution of acute infectious gastroenteritis  Infectious gastroenteritis should be defined by positive stool culture in a symptomatic individual or presence of two of the following acute symptoms (when stool culture not available):  fever vomiting diarrhea  Exclusion Criteria:  Patients should not meet criteria for IBS before onset of acute illness. We will exclude patients who are pregnant, who have an oncology history (since these patients might exhibit diarrhea due to their underlying illness) and patients with alcohol dependence (due to the non-compliance shown by these patients) and patients with known hypersensitivity or allergy to any of the ingredients included in Gelsectan.