BACKGROUND: A diet low in fermentable oligo-, di-, monosaccharides and polyols (LFD) improves symptoms in patients with irritable bowel syndrome (IBS). Previous studies have focused on patients with IBS and diarrhea (IBS-D). It is unclear whether LFD is effective for IBS with constipation (IBS-C) or IBS with mixed bowel habits (IBS-M). This open-label, real-world study evaluates the relative effectiveness of the LFD among IBS subtypes.
METHODS: This study analyzes data from a service that provides low-FODMAP meals to individuals with IBS. Participants met with a registered dietitian and completed the IBS symptom severity survey (IBS-SSS) before and after undergoing a 2-4-week period of FODMAP restriction. The primary endpoint was the proportion of participants with ≥50-point decrease in IBS-SSS between the three IBS subtypes.
RESULTS: After FODMAP restriction, 90% of participants with IBS-D, 75% with IBS-C, and 84% with IBS-M met the primary endpoint (p = 0.045). Similar improvement was seen for a 100-point decrease, but the difference between IBS subtypes was not significant (p = 0.46). After FODMAP restriction, all groups had statistically significant improvement in total IBS-SSS as well as individual symptom categories. Improvement in IBS-SSS subcategories was similar among the groups except for the categories of bloating severity (IBS-M had greatest improvement) and bowel movement satisfaction (IBS-C had less improvement).
CONCLUSIONS: Though the proportion of responders was highest for IBS-D and lowest for IBS-C, the LFD led to robust improvement in overall symptoms in all IBS subtypes. Key individual symptoms also showed significant improvements in all IBS subtypes.

Diet is an environmental exposure implicated in the development of inflammatory bowel disease (IBD), including Crohn\'s disease (CD) and ulcerative colitis (UC). Dietary therapy is also a tool for management of these conditions. Nutrition therapy for IBD has been shown to reduce intestinal inflammation, promote healing, and alleviate symptoms, as well as improve patients\' nutrition status. Although the mechanisms of action of most nutrition therapies for IBD are not well understood, the diets are theorized to eliminate triggers for gut dysbiosis and mucosal immune dysfunction associated with the typical Western diet. Exclusive enteral nutrition and the Crohn\'s disease exclusion diet are increasingly being used as the primary treatment modality for the induction of remission and/or maintenance therapy in children, and in some adults, with CD. Several other diets, such as the Mediterranean diet, anti-inflammatory diet for IBD, and diets excluding gluten, FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols), lactose, or other compounds, may be helpful in symptom management in both CD and UC, though evidence for biochemical efficacy is limited. In this review, we discuss the role of diet components in IBD pathogenesis and examine diets currently used in the management of children and adults with IBD. We also address practical, psychosocial, and cultural considerations for dietary therapy across diverse populations.