Dose-dependent FODMAP Reintroduction in IBS (DORI)

Inclusion Criteria: Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures Use of highly effective methods of birth control; defined as those that, alone or in combination, result in low failure rate (i.e., less than 1% per year) when used consistently and correctly; such as implants, injectables, combined oral contraceptives, some IUDs, true sexual abstinence (i.e. refraining from heterosexual intercourse during the entire period of risk associated with the Trial treatment(s)) or commitment to a vasectomised partner. Patients with irritable bowel syndrome according to Rome IV diagnostic criteria Patients ages between 18 and 70 years old Exclusion Criteria: 1. Participant has a history of any major psychiatric disorders (including those with a major psychosomatic element to their gastrointestinal disease), depression, alcohol or substance abuse in the last 2 years Any disorder, which in the Investigator's opinion might jeopardise the participant's safety or compliance with the protocol Any prior or concomitant treatment(s) that might jeopardise the participant's safety or that would compromise the integrity of the Trial Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using an adequate, highly effective contraceptive Participation in an interventional Trial with an investigational medicinal product (IMP) or device Patients presenting with predominant symptoms of functional dyspepsia (FD) and of gastro-oesophageal reflux disease (GERD) Patients following a diet interfering with the study diet in opinion of the investigator Patients who already followed the low FODMAP diet under guidance of a trained dietitian without success.