S2154 Effects of a Low FODMAP Diet on Gut Microbiota in Inflammatory Bowel Disease: A Systematic Review

Introduction: The low FODMAP diet (LFD) is commonly used to alleviate gastrointestinal symptoms in patients with quiescent inflammatory bowel disease (IBD), especially those experiencing irritable bowel syndrome–like symptoms. While its short-term efficacy is well-supported, the diet’s effects on gut microbiota composition remain unclear. Methods: We conducted a systematic review of randomized controlled trials (RCTs) following PRISMA guidelines. A comprehensive search of PubMed, Embase, Scopus, and Web of Science through March 2025 identified studies involving adults with IBD who underwent a LFD intervention with pre- and post-diet microbiota assessment. Two reviewers independently screened records, extracted data, and assessed risk of bias using the Cochrane RoB-2 tool. Outcomes included microbial composition, short-chain fatty acid (SCFA) levels, gastrointestinal symptoms, inflammatory markers, and quality of life. Results: Out of 3,421 records screened, 2 RCTs (n = 61) met inclusion criteria. In Cox et al. (n = 52), 52% of patients on the LFD reported adequate symptom relief compared to 16% in the control group (P = 0.007). Halmos et al. (n = 9) also observed reductions in bloating, flatulence, and abdominal pain. However, both studies showed consistent alterations in gut microbiota. Notably, the LFD was associated with significant reductions in Faecalibacterium prausnitzii (P < 0.038), Bifidobacterium adolescentis (P < 0.003), B. longum (P < 0.005), and Clostridium cluster XIVa (P < 0.008)—key butyrate-producing and immunoregulatory taxa. Akkermansia muciniphila (P < 0.016), critical for mucosal barrier integrity, also declined. Although Ruminococcus torques (P < 0.039), a potentially pathogenic mucus-degrading species, decreased as well, the overall microbial shifts resembled dysbiosis typically seen in active IBD. Fecal SCFA levels were lower in the LFD group, though not significantly. No significant changes were observed in CRP or fecal calprotectin levels. Conclusion: The low FODMAP diet provides effective short-term relief of gastrointestinal symptoms in patients with quiescent IBD. However, it also leads to reductions in beneficial gut microbial taxa and SCFA production, raising concerns regarding its long-term impact. Further long-term RCTs are warranted to evaluate the diet’s influence on disease progression and relapse risk.