The study is a randomized, double-blind, cross-over trial.~The aim is to assess the effects of low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet compared to moderate/high FODMAP diet in IBS patients on gastrointestinal symptoms and psychological factors. The primary hypothesis is that the low FODMAP diet decreases gastrointestinal symptoms compared to moderate/high FODMAP diet, and that this change is accompanied with reduced psychological distress.~IBS patients (Rome IV) are challenged with FODMAPs in this randomized, double-blinded, cross-over study. The subjects will start with the low FODMAP diet or moderate/high FODMAP diet and cross over to the other intervention (both for 7 days). In between the interventions, there is a wash-out period of at least 14 days. The subjects will receive ready-made meals from the hospital kitchen (lunch and dinner) and in between snacks. The subjects are instructed to buy breakfast themselves and the subjects will receive information on which other foods to avoid, without mentioning 'FODMAPs'. The subjects will follow their usual diet (as before initiation of the study) during the wash-out period.~Primary outcomes are change in gastrointestinal symptoms, assessed by questionnaires, including IBS Severity Scoring System (IBS-SSS) (7-10 day recall and modified daily) and Gastrointestinal Symptom Rating Scale -IBS (GSRS-IBS). A 50-point reduction in IBS-SSS indicates clinical response. Bacterial fermentation (exhaled hydrogen and methane) and visceral sensitivity will be measured using the Lactulose Nutrient Challenge Test. Secondary outcomes are change in psychological factors and assessed by questionnaires, including Central Sensitization Index (CSI), Hospital Anxiety and Depression Scale (HADS), Patient Health Questionnaire (PHQ)-15 and Visceral Sensitivity Index (VSI).
Patients with Irritable Bowel Syndrome (IBS) often link their symptoms to foods. Interest in dietary management recently increased, including the use of a low FODMAP diet.~To investigate relation of FODMAPs and IBS, a randomized, double-blind, cross-over trial will be carried out in adult (>18) patients with IBS according to Rome IV criteria. The aim is to assess low FODMAP diet versus moderate/high FODMAP diet in IBS patients.