Comparison Between Low FODMAP and SSRD in IBS

Comparison in the Effects and Mechanisms Between Low Fermentable-, Oligo-, di-, and Monosaccharides and Polyols (FODMAP) and Starch- and Sucrose-reduced Diet (SSRD) in Irritable Bowel Syndrome (IBS)

The aim of the present study is to compare the efficiency of low FODMAP and SSRD to reduce symptoms in IBS, and to study the mechanisms and consequences of the two diets.

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.

The participants are given oral and written instructions on which diet that contains low contents of FODMAP.

The participants are given oral and written information about each diet. No food is delivered from the investigator to the participant

To assess bowel symptoms and extra-intestinal symptoms after the dietary interventions by evaluation of irritable bowel syndrome-symptom severity score (IBS-SSS). This questionnaire contains VAS scales ranging from 0-100 where a higher score means worse symptoms.

To assess bowel symptoms and extra-intestinal symptoms after the dietary interventions by evaluation of IBS-SSS. This questionnaire contains VAS scales ranging from 0-100 where a higher score means worse symptoms.

To assess bowel symptoms after the dietary interventions by evaluation of visual analog scale for irritable bowel syndrome (VAS-IBS). This questionnaire contains VAS scales ranging from 0-100 where a higher score means worse symptoms.

To assess bowel symptoms after the dietary interventions by evaluation of visual analog scale for irritable bowel syndrome (VAS-IBS). This questionnaire contains VAS scales ranging from 0-100 where a higher score means worse symptoms.

The investigator will analyze plasminogen activator inhibitor-1 (PAI-1) by enzyme-linked immunosorbent assay (ELISA) to see and compare the effects of the two different diets.

The investigator will analyze C-peptide by enzyme-linked immunosorbent assay (ELISA) to see and compare the effects of the two different diets.

The investigator will analyze insulin by enzyme-linked immunosorbent assay (ELISA) to see and compare the effects of the two different diets.

The investigator will analyze leptin by enzyme-linked immunosorbent assay (ELISA) to see and compare the effects of the two different diets.

The investigator will analyze GIP by enzyme-linked immunosorbent assay (ELISA) to see and compare the effects of the two different diets.

The investigator will analyze visfatin by mesoscale to see and compare the effects of the two different diets.

The investigator will analyze ghrelin by mesoscale to see and compare the effects of the two different diets.

The investigator will analyze fecal microbiota by whole genome sequencing to see and compare the effects of the two different diets

The investigator will analyze DNA methylation to see and compare the effects of the two different diets

The investigator will analyze sucrase-isomaltase (SI) genes to see if the genetic profile hais of importance for the clinical effect of the two diets

The investigator will analyze values of vitamin A in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of vitamin B in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of vitamin C in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of vitamin D in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of phosphorous in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of zinc in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of magnesium in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze values of albumin in blood before and after the study to compare the effects on the nutritional status by the two diets.

The investigator will analyze metabolomics and proteomics in blood to see and compare the effects of the two different diets

Effects on quality of life by RAND-36 (comprehensive short-form generic profile for health-related quality of life (HRQoL))

The investigator will analyze how the two different diets influence quality of life, measured by RAND-36, to compare the effects of the two different diets. RAND-36 is comprised of 36 items on 5-point Likert scale, the higher score the better quality of life, that assess eight health concepts: physical functioning, role limitations caused by physical health problems, role limitations caused by emotional problems, social functioning, emotional well-being, energy/fatigue, pain, and general health perceptions.

The investigator will analyze how the two different diets influence eating disturbances measured by SCOFF, to compare the effects of the two different diets. SCOFF contains 5 questions answered by "yes" or "no": 1) Do you make yourself Sick because you feel uncomfortably full?, 2) Do you worry that you have lost Control over how much you eat?, 3)Have you recently lost more than One stone (14 lb) in a 3-month period?, 4)Do you believe yourself to be Fat when others say you are too thin?, and 5) Would you say that Food dominates your life?

The investigator will analyze how the two different diets influence healthcare consumption by asking the participants about how many times they have visited a Healthcare giver before, during and after the study, to compare the effects of the two different diets

Inclusion Criteria: Verified IBS according to Rom IV criteria. Exclusion Criteria: Serious mental disease Serious somatic disease Abuse Inability to understand the Swedish language Already on a diet