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Traditional dietary advice is the best first approach for patients with non-constipated irritable bowel syndrome (IBS), with the low FODMAP diet (LFD) and gluten-free diet (GFD) reserved for specific patients, researchers said.

In a randomized trial of 99 patients, a ≥50-point reduction in IBS symptom severity score (IBS-SSS) after 4 weeks was seen for 58% of those who followed the GFD, 55% of those who followed the LFD, and 42% of those who followed traditional dietary advice (P=0.43), reported Imran Aziz, MD, of the Sheffield Teaching Hospitals NHS Foundation Trust in England.

"On balancing the efficacy and acceptability of dietary therapies, plus the demands they place upon healthcare services, we suggest traditional dietary advice be considered first," the authors wrote in . "We suggest a GFD or LFD be reserved according to specific patient preferences and with specialist dietetic input."

Compared with the GFD and LFD, IBS patients found that traditional dietary advice was cheaper (P<0.01), quicker to shop for (P<0.01), and easier to follow when dining out (P=0.03), Aziz and team noted.

Reached for comment, Eamonn Quigley, MD, of Houston Methodist and past president of the American College of Gastroenterology, called the study findings "very important and long-overdue."

"Dietary studies are tough to do, but much needed in order to deal with all the hype and hoopla about all sorts of diets in IBS," said Quigley, who was not involved in the research. "They have wisely chosen to study the three most relevant to IBS."

Dietary therapies are often recommended for patients with IBS, since more than 80% experience food-related symptoms, and 63% remain eager to understand what foods to avoid, the authors said. Traditional dietary advice includes the adoption of sensible and healthy eating patterns, including having regular meals with proper portion sizes, maintaining hydration, and reducing processed, fatty, gas-producing foods, in addition to carbonated and alcoholic beverages.

The LFD initially prohibits fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) foods, commonly found in wheat and dairy, for 4 to 6 weeks, since they can increase intestinal fluids and gas causing gastrointestinal symptoms, followed by a personalized gradual re-introduction.

The GFD has also proven effective in IBS patients, since about 10% of people report that gluten-based foods stimulate IBS-compatible intestinal symptoms. Minimal evidence exists on which diet is superior for IBS and some remain concerned that restrictive diets could lead to detrimental nutritional and stool microbial alterations.

While overall reductions in micro- and macro-nutrient intake were similar across the diets in this study, the patients in the LFD group had the highest reduction in total FODMAP content from pre-intervention to week 4 (27.7 to 7.6 g/day) compared with the GFD (27.4 to 22.4 g/day) and traditional dietary advice (24.9 to 15.2 g/day; P<0.01).

Stool dysbiosis index alterations were also similar across the diets, with 35% to 40% of patients showing an increase in dysbiosis, 35% to 39% showing no change, and 22% to 29% showing reduced dysbiosis.

For this study, Aziz and colleagues examined data on 99 patients with Rome IV-defined non-constipated IBS and randomized them 1:1:1 to the LFD, GFD, or traditional dietary advice. Participants were recruited from two U.K. centers and were eligible if they had IBS-diarrhea or mixed-type IBS, with an IBS-SSS of >75.

Most patients were white (88%), 71% were women, mean age was 37, and baseline IBS-SSS was 301. Three-fourths had IBS-diarrhea, while the rest had mixed-type IBS. Moderate IBS was more common than severe or mild IBS cases (47%, 45%, and 9% of patients, respectively).

Patients participated in a face-to-face or virtual educational presentation on their allocated diet with a dietitian lasting nearly an hour and received dietary informational sheets.

Stool samples were collected pre- and post-dietary intervention, and several questionnaires were completed. Outcomes were assessed at 4 weeks and compared to baseline.

Slightly more patients who followed traditional dietary advice considered continuing their diet (70%) compared with those who followed the LFD (67%) or GFD (61%).

Aziz and colleagues acknowledged some limitations to their data, including the fact that they excluded patients with IBS-constipation, since reducing FODMAP intake might worsen constipation and overall symptoms; however, evidence suggests that the LFD might benefit these patients and further study is warranted.

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