Introduction: A diet low in FODMAPs (LFD) is only effective in 50-60% of patients with irritable bowel syndrome (IBS) and is restrictive, time-consuming, and carries the risk of nutritional deficiencies. Therefore, there is a need for novel dietary therapies for IBS. A recent pilot randomized controlled trial (RCT) found the Mediterranean diet (MD) to be superior to habitual diet in IBS. However, MD has not been compared to LFD in a head-to-head trial. In this pilot feasibility, blinded, RCT we compared the efficacy of MD and LFD in patients with IBS.
Methods: Adult patients (18-70 years) meeting the ROME IV definition of diarrhea-predominant IBS (IBS-D) or IBS with mixed bowel pattern (IBS-M) with an average pain intensity (API) score ≥3.0 during the 7-day baseline period were randomized to MD vs. LFD for 4 weeks. Meals for both groups were provided by a food delivery company (ModifyHealth, GA), and daily food logs were recorded. For the meals provided, the average FODMAP content per meal was 0.36 in the LFD group vs. 1.51 grams in the MD group (P<0.0001). Daily variables included API, abdominal discomfort, bloating, and bowel habits. IBS symptom severity score (IBS-SSS) and IBS adequate relief (IBS-AR) were scored weekly. The primary endpoint was the proportion of patients meeting the FDA endpoint for API (≥30% decrease in the weekly average of daily API during ≥2 of the 4-week treatment period).
Results: Of 26 randomized patients, 20 finished the study and were included in the analysis (10 in each group). Ninety percent of the patients in the LFD group met the primary endpoint compared to 80% in the MD group (P=1.0). All patients in the LFD group (10/10) had a ≥30% decrease in the average bloating scores for ≥2/4 weeks compared to 7/10 patients in the MD group (P=0.21). A higher proportion of patients in the LFD group reported adequate relief and met the responder endpoint for IBS-SSS (50-point reduction) for at least 2/4 weeks compared to the MD group (60 vs. 30% for IBS-AR and 90% vs. 50% for IBS-SSS, P=0.37 and 0.14 respectively). Similarly, the LFD group had a significantly higher decrease in IBS-SSS over a 4-week treatment period compared to the MD group (-105.5 vs. -60, P=0.02). The percent decrease in average weekly scores for API, abdominal discomfort, and bloating between week 4 and the baseline period was also higher in the LFD group compared to the MD group, however, this did not reach statistical significance (Table 1).
Conclusion: In the first randomized-controlled feeding study directly comparing the efficacy of MD with LFD, we found MD is feasible in IBS-D and IBS-M. While MD provides symptom relief in a subset of patients, the magnitude of relief was lower compared to the LFD. Larger studies in real-world settings comparing the efficacy of the LFD or NICE diet are needed before MD can be routinely recommended to IBS patients.

Christine Lothen-Kline

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