Efficacy of Mediterranean Diet vs. Low-FODMAP Diet in Patients With Nonconstipated Irritable Bowel Syndrome: A Pilot Randomized Controlled Trial

Introduction: Mediterranean diet (MD) has been proposed as a dietary therapy for irritable bowel syndrome (IBS) but its efficacy remains unclear. We compared the efficacy of MD to a diet low in fermentable oligo-, di-, monosaccharides, and polyols (LFD). Methods: In this pilot-feasibility, randomized controlled trial (RCT), adult patients with diarrhea-predominant IBS (IBS-D) or mixed bowel pattern (IBS-M) were randomized to MD versus LFD for 4 weeks. Meals were provided for both groups (ModifyHealth, GA). Daily variables included abdominal pain intensity (API) and bloating, while IBS symptom severity score (IBS-SSS) and IBS adequate relief (IBS-AR) were scored weekly. The primary endpoint was the proportion of patients with ≥ 30% decrease in API for ≥ 2/4 weeks. Results: Of 26 randomized patients, 20 finished the study (10 per group). Seventy-three percent of the MD group met the primary endpoint compared to 81.8% of the LFD group (p = 1.0). Although not statistically significant, a numerically higher proportion of the LFD group reported adequate relief and met the responder endpoint for IBS-SSS (50-point reduction) compared to the MD group (54.6% vs. 27.3% for IBS-AR and 81.8% vs. 45.5% for IBS-SSS, p = 0.39 and 0.18, respectively). The LFD group also had a significantly greater reduction in IBS-SSS score over the 4-week treatment period compared to the MD group (−105.5 vs. −60, p = 0.02). Conclusion: MD provides symptom relief in IBS-D and IBS-M; however, the magnitude of relief was higher with the LFD. Larger diet comparison studies in real-world settings are needed before MD can be routinely recommended to IBS patients. Trial Registration: Clinicaltrials.gov: NCT05807919.