Comparison Between Low FODMAP and SSRD in IBS

The investigator will perform a study on 200 subjects with verified irritable bowel syndrome (IBS). Participants will be recruited from the clinic of Gastroenterology or Internal medicine as well as primary health care centers. At the start of the study, participants will complete protocols concerning Rom IV criteria (to validate that the IBS criteria are ful-filled) as well as IBS symptom rating scales irritable bowel syndrome-symptoms severity scores (IBS-SSS) and visual analog scale for irritable bowel syndrome (VAS-IBS). The Item Health Survey 1.0 (distributed by RAND), RAND-36, includes the same items as those in the Short-Form Health Survey (SF-36), and evaluates the quality of Life. SCOFF is a brief questionnaire that asks the five questions about eating disturbances (Do you make yourself Sick because you feel uncomfortably full? Do you worry you have lost Control over how much you eat? Have you recently lost more than One stone in a 3 month period? Do you believe yourself to be Fat when others say you are too thin? Would you say that Food dominates your life?). Participants will be examined by an investigator who will complete protocols of clinical data. Blood and fecal samples will be collected by the investigator.

Study participants will thereafter be randomized to receive either low FODMAP (Fermentable, Oligo-, Di-, Mono-saccharides And Polyols) diet (n=100), or a SSRD diet (starch ans sucrose-reduced diet) (n=100). After 4 weeks of dietary intervention, there will be a follow-up where blood and fecal samples are once again collected. At this point in time, participants will also fill in IBS symptom rating scales again.

The participants are then free to eat whatever they want to, and another 5 months later, they will be examined again, the same protocols will be completed, and blood and fecal samples are collected.

The investigator will use samples from baseline, 4 weeks and 6 months, for genetic/epigenetic (including genomic-wide association studies), metabolomics, proteomics, nutritional data, gut microbiota, and inflammatory parameter analyses.

Statistics

The investigator will use Mann-Whitney U-test and Wilcoxon test to study differences in the above-mentioned parameters between the two treatment groups, as well as before and after dietary intervention, respectively. For analyses of genetic/epigenetics, metabolomics, proteomics, and microbiota, the investigator will use bioinformatics and biostatistics.

• Effects on plasminogen activator inhibitor-1 (PAI-1) [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on C-peptide [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on insulin [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on leptin [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on gastric inhibitory peptide (GIP) [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on visfatin [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on ghrelin [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on gut microbiota by whole genome sequencing of feces [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on microRNA [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on DNA methylation [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects depending on genetics [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]
• Effects on vitamin A [Time frame: 4 weeks dietary intervention, with a follow-up after another 5 months]