Food-related symptoms, dietary interventions, and importance of the gut microenvironment in IBS

Abstract

Irritable bowel syndrome (IBS) is characterized by chronic gastrointestinal (GI) symptoms, including abdominal pain and altered bowel habits i.e., constipation and diarrhea. The pathophysiology is complex and multifactorial and many IBS patients report their symptoms to be associated with certain food items, including gluten and carbohydrates. Two of the most common dietary interventions in IBS are the gluten-free diet and a diet low in specific carbohydrates i.e., fermentable oligo-, di-, monosaccharides, and polyols (FODMAP). In this thesis, the overall aim was to assess if dietary interventions can improve GI symptoms through specific dietary and physiologic mechanisms in IBS. Study I assessed the daily intake of gluten and associations with GI symptoms in IBS. IBS patients ingested 11g of gluten per day, and patients with lower intake of gluten had more severe symptoms. It may be the case that IBS patients with severe symptoms attempt to alleviate their symptoms by reducing gluten intake. Study II compared the effects of gluten-free and gluten-containing diets in IBS and healthy individuals. The gluten-free diet did not improve GI symptoms compared with the gluten-containing diet and should not be recommended to all IBS patients. However, a subset of IBS patients improved on the gluten-free diet and metabolites produced by the gut microbiota may potentially predict the response to a gluten-free diet. Study III compared the effects of diets with low and moderate FODMAP content in IBS. The low FODMAP diet reduced GI symptoms compared with the moderate FODMAP diet, and a low FODMAP diet can be recommended to IBS patients. Both gluten-free and low FODMAP diet reduced the reports of loose stools, suggesting that dietary interventions could be more effective in non-constipated IBS. Study IV assessed associations between postprandial symptoms and several physiologic mechanisms in IBS, including transit time, rectal sensitivity, and hydrogen/methane production. Transit time, hydrogen/methane production, and (postprandial) GI symptoms are reciprocally associated, highlighting the importance of GI motility and the gut microenvironment in the pathophysiology of IBS. Measures of transit time could provide guidance on relevant treatments. In summary, this thesis provides insights on mechanisms and associations involved in food-related symptoms, on efficacy of dietary interventions, and the importance of the gut microenvironment in IBS.