The Mediterranean diet was both noninferior and superior to traditional dietary advice in reducing symptom severity among patients with irritable bowel syndrome (IBS) in a randomized clinical trial conducted in the UK. 

These results suggest that the Mediterranean diet represents a “viable first-line dietary intervention for IBS,” wrote the study authors, led by Joy O. Bamidele, BMedSci, from the School of Medicine and Population Health, University of Sheffield, England.

However, the mechanisms by which the Mediterranean diet improves the symptoms of IBS are unclear, they noted. “Aspects of this diet include consuming FODMAP-rich foods (for example, grains, fruit and vegetable, and pulses), as reflected in our study with the increase in the levels of oligosaccharides,” they wrote. 

The study was published online in the Annals of Internal Medicine. 

Practice-Changing? 

IBS affects 5%-10% of people worldwide, often leading to chronic abdominal pain, bloating, and altered bowel habits. Because symptoms are frequently food-related, many patients turn to diet for relief.

Current guidelines recommend starting with traditional dietary advice — which promotes balanced, moderate eating and limits irritants like caffeine, alcohol, and fatty foods — before moving to the low FODMAP diet, a restrictive approach that removes certain fermentable carbohydrates.

While the low FODMAP diet can be effective, it’s complex, costly, and socially restrictive and often requires specialist supervision. The Mediterranean diet, in contrast, is easier to follow, more nutritionally balanced, and has proven cardiovascular and mental health benefits, making it a promising alternative.

Bamidele and colleagues designed their trial to see if the Mediterranean diet is at least as effective as traditional dietary advice for improving IBS symptoms. They enrolled 139 adults (mean age 40 years; 80% women) who met Rome IV diagnostic criteria for IBS. 

The mean IBS Symptom Severity Scale (IBS-SSS) at baseline was 309 (range, 0-500 points), with 9% having mild IBS, 37% having moderate IBS, and 54% having severe IBS. Nearly half (48%) had IBS-mixed pattern, 31% with IBS-diarrhea predominant, and 21% with IBS-constipation predominant. 

The researchers randomly allocated 68 study participants to the Mediterranean diet (rich in fruits, vegetables, legumes, whole grains, fish, and olive oil) and 71 to traditional healthy eating advice. Each group had an online session with a dietitian to learn about their diet. 

The two groups were well balanced and adherence to both diets was “excellent,” the authors reported. 

By the end of the 6-week study period, 62% of participants following the Mediterranean diet achieved a clinically meaningful 50-point or greater reduction in IBS-SSS compared with 42% following traditional dietary advice. 

This 20-percentage-point difference was statistically significant (P = .017) and demonstrated not only noninferiority but also superiority of the Mediterranean diet over traditional healthy eating advice in reducing IBS symptoms.

At week 6, 44% of the Mediterranean diet group had achieved a 100-point reduction in IBS-SSS compared with 32% of the traditional diet advice group — a difference of 13 percentage points favoring the Mediterranean diet. 

The mean reduction in IBS-SSS was also greater in the Mediterranean diet group (-101 vs -65 points; P = .034).

In subgroup analyses, participants with moderate or severe IBS benefited most from the Mediterranean diet, while effects were less clear in those with mild symptoms, although the number of patients in this subgroup was small. 

There were no statistically significant between-group differences in mood, somatic symptoms, quality-of-life, or diet satisfaction, but the Mediterranean diet led to a greater reduction in the frequency of abdominal pain. 

Important Study, With Caveats

“In my opinion, based on this data, it is definitely reasonable to recommend a Mediterranean diet for patients with IBS,” said Ashwin Ananthakrishnan, MD, MPH, gastroenterologist at Massachusetts General Hospital and Harvard Medical School, Boston, who was not involved in the research. 

“This is an important study and is much needed in the field, as there are few dietary studies that adopt a high-quality randomized controlled design,” he told Medscape Medical News.

However, he said “an important caveat” is that the study did not compare the Mediterranean diet to the low FODMAP diet, which also has strong evidence of benefit. “Thus, a follow-up study comparing the Mediterranean Diet to other active dietary interventions that have also demonstrated benefit is necessary to understand which diet is the best for patients with IBS,” he explained. 

Ananthakrishnan acknowledged the practical challenges in carrying out dietary intervention studies and the need for longer-term studies. 

“Understandably, this study only looked at outcome at 6 weeks. For life-long fluctuating diseases like IBS, it is important to examine the impact of dietary interventions over a longer time frame to understand sustained benefit. For example, do patients go on a Mediterranean Diet only during their IBS flare ups or do they need to stay on it long-term?” he wondered.

The study had no commercial funding. The authors and Ananthakrishnan had no relevant disclosures.