The aim of the present study is to research whether subjects with irritable bowel syndrome (IBS) display epigenetic/genetic changes or altered microbiota compared to a non-IBS control group. Further, we will investigate if these parameters as well as subjective IBS symptoms are affected by a 4-week long dietary intervention within the IBS patient group.

The study will be performed on 140 subjects with verified IBS. Patients will be recruited from the clinic of Gastroenterology or Internal medicine as well as primary health care centers. At the start of the study patients will fill out protocols concerning Rom IV criteria (to validate that IBS criteria are filled) as well as IBS symptom rating scales. They will be examined by a physician/researcher who will complete protocols of clinical data. Blood and fecal samples will be collected. A control group of healthy, non-IBS individuals will go through the same procedure as described above.

Study participants with IBS will thereafter be randomized to receive an alternative diet resembling the FODMAP (Fermentable, Oligo-, Di-, Mono-saccharides And Polyols) diet (n=130), or to continue with their regular diet (control group; n=20). 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.

Samples from baseline and 4 weeks will be used for genetic/epigenetic (including genomic-wide association studies), gut microbiota and inflammatory parameter analyses.

Statistics

To study differences in the above-mentioned parameters between patients and controls as well as before and after dietary intervention, Mann-Whitney U-test and Wilcoxon test will be used, respectively.

Inclusion Criteria:

• Verified IBS according to Rom IV criteria.

Exclusion Criteria:

• Serious mental or somatic disease
• Abuse
• Inability to understand he Swedish language
• Already on a diet (e.g. vegan, FODMAP, gluten-free).