The goal of this interventional study is to examine whether those patients with irritable bowel syndrome (IBS) and a reduced abitility do degrade starch and sugar (lowe levels of enzymes) have lower raise in blood glucose after a meal than those with normal expression of enzymes. We also want to examine whether those IBS patients with reduced enzyme levels have increased bowel symptom in relation to this meal.

The main questions it aims to answer are:

Does reduced ability to degrade starch and sugar due to less enzyme activity lead to lower increase in blood glucose after a meal? Does reduced ability to degrade starch and sugar due to less enzyme activity lead to increased bowel symptoms after a meal?

All IBS patients who have been included in the previous studies (Dnr 2017/171, Dnr 2021-05407-01 and Dnr 2023-01377-01) and have been genetically tested for the sucrase-isomaltse enzyme (SI gene) and other genes encoding enzymes important for carbohydrate absorption will be called and asked if they want to participate in the present study.

The patient receives a basic questionnaire about lifestyle, health and symptoms over the past 2 weeks, including Rome IV questionnaire, irritable bowel syndrome-severity scoring system (IBS-SSS), and visual analog scale for irritable bowel syndrome (VAS-IBS) to be completed at home and brought to the test. The patient comes to the clinic fasting (only allowed to drink water at home in the morning). A plastic tube is placed in the arm, and the patient has to eat a sugar-rich meal during 15 minutes. Blood samples are drawn 10 minutes before start, at the start of the meal, and 10, 20, 30, 45, 60, 90, och 120 minutes aftrewards. Blood samples are analyzed for glucose levels in blood at the Department of Clinical Chemistry, at the hospital. At the same time points as blood sampling, the patient has to complete a questionnaire about bowel symptoms.

Raise in blood glucose and bowel symptoms will be compared between those with reduced enzyme activity and those with normal enzyme activity. The correlation between blood glucose levels and symptoms will be calculated.

Inclusion Criteria:

• Diagnosis of irritable bowel syndrome (IBS)
• Gene testing has been conducted regarding genes regulating the production of sucrase-isomaltase ensymes in previous dietary interventions using the starch- and sucrose reduced diet (SSRD) or multi-center study.

Exclusion Criteria:

• Diagnosis of inflammatory bowel disease, celiac disease, bile salt malabsorption, gastroenteritis or enteric dysmotility
• Severe food allergy
• Serious heart-, lung-, cardiovascular-, malignant- or mental illness
• Ongoing eating disorder
• Pregnancy
• Recent major gastrointestinal surgery
• Alcohol and/or drug addiction

Due to ethical rules in Sweden, we can not share individual data. The participants have written an informed concent that data will be presented group wise.