Bamidele, Joy O (JO);Brownlow, Grace M (GM);Flack, Rosie M (RM);Buckle, Rachel L (RL);Shaw, Christian C (CC);Shiha, Mohamed G (MG);Aziz, Imran (I);

Author information

Ann Intern Med.2025 Oct 28;178(12):1709-1717.doi:10.7326/ANNALS-25-01519

Abstract

BACKGROUND: Patients with irritable bowel syndrome (IBS) frequently seek dietary advice, but few evidence-based options exist. Major societal guidelines recommend traditional dietary advice (TDA) as first-line therapy, with the cumbersome and resource-intensive low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet reserved as second-line therapy. Recent pilot data suggest that the Mediterranean diet (MD), renowned for its general health benefits, improves IBS symptoms, but whether it can be considered another first-line dietary option is unknown.

OBJECTIVE: To determine if the MD is noninferior to TDA in managing IBS symptoms.

DESIGN: Randomized noninferiority clinical trial. (ClinicalTrials.gov: NCT05985018).

SETTING: Online virtual platform.

PARTICIPANTS: 139 persons with IBS from across the United Kingdom.

INTERVENTION: 6 weeks of the MD (= 68) or TDA (= 71).

MEASUREMENTS: Primary end point was the proportion achieving clinical response, defined as 50-point or greater reduction in IBS Symptom Severity Scale (IBS-SSS). Secondary outcomes included changes in IBS-SSS scores, psychological health, somatic symptom reporting, quality of life, diet satisfaction, and Mediterranean Diet Adherence Screener (MEDAS).

RESULTS: Baseline characteristics (mean age, 40.4 years [range, 19 to 65 years]; 80% women) and IBS-SSS (mean, 309 [SD, 90]) were similar between groups. On modified intention-to-treat analysis, the primary end point was met by 62% (95% CI, 50% to 73%) following a MD versus 42% (CI, 31% to 55%) following TDA. The difference in clinical response favored the MD (difference, 20 percentage points [CI, 4 to 36 percentage points];  = 0.017), demonstrating noninferiority and superiority. There was a greater reduction in the mean IBS-SSS after a MD than TDA (-101.2 vs. -64.5; Δ-36.7 [CI,-70.5 to -2.8];  = 0.034). No statistically significant differences were seen between the groups with regard to changes in mood, somatic symptoms, quality of life, or diet satisfaction. The MEDAS significantly increased after a MD compared with TDA ( < 0.001).

LIMITATION: No long-term data.

CONCLUSION: The MD showed noninferiority and superiority to TDA in managing IBS symptoms. It represents a viable first-line dietary intervention for IBS.

PRIMARY FUNDING SOURCE: None.