Is Combining Low-FODMAP/Gluten-Free the Answer?

For adults with irritable bowel syndrome (IBS), combining a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) and a gluten-free diet (GFD) appears to improve clinical symptoms and reduce anxiety and depression, according to a new systematic review and meta-analysis.

Across several studies, the combined diet improved quality of life and reduced bloating, stomach pain, and the severity of IBS symptoms, lead author Jing Zhang of the Yangzhou University School of Nursing in Jiangsu, China, and colleagues found.

“Dietary therapies have attracted a lot of interest lately as a possible method to control IBS symptoms. Among these, the low-FODMAP diet has shown especially great promise,” the researchers wrote.

The GFD also has become a potential dietary intervention for certain IBS subtypes. Some studies have looked at the combination of both for IBS management.

However, the “small and inconclusive” nature of existing research prompted their review of the efficacy of a low-FODMAP combined with a gluten-free diet (LF-GFD) in adult patients with IBS, the authors wrote.

The study was published online in Digestive Diseases and Sciences.

Analyzing RCTs and Cohort Studies

Zhang and colleagues analyzed data for 437 patients with IBS (221 on a LF-GFD and 216 on a GFD) across four randomized controlled trials (RCTs) and four cohort studies.

The research team evaluated the efficacy of an LF-GFD in reducing symptoms using measures such as the visual analog scale for bloating and pain, IBS symptom severity scale, and IBS quality of life questionnaire, as well as self-reported depression and anxiety scales.

Overall, combined results across the eight studies indicated that a LF-GFD reduced bloating (rate ratio [RR], -0.58), pain (RR, -0.42), and symptom severity (mean difference [MD], -1.42), and improved quality of life (MD, 3.75).

Patients in the LF-GFD group also had reductions in self-reported depression scores (MD, -2.56) and self-reported anxiety scores (MD, -4.3) compared to the GFD group.

The findings imply that a combination of the two diets is an effective intervention for improving clinical IBS symptoms, but more research is needed, the authors wrote. 

They also noted that the analysis has several limitations, including the small number of RCTs and different intervention lengths across the studies. 

Dietary Considerations 

Dietary interventions are a logical place to focus when developing IBS treatment strategies because more than three-quarters of patients with the condition relate their GI symptoms to eating a meal, William Chey, MD, professor of nutrition sciences and chief of gastroenterology and hepatology at Michigan Medicine in Ann Arbor, Michigan, told Medscape Medical News.

Chey, who wasn’t involved with this study, has researched low-FODMAP diets among patients with IBS.

“In patients with IBS, food is very emotionally charged, both in ways good and bad,” he said. “These biases make it really important to conduct methodologically rigorous clinical trials to determine fact versus fiction regarding diet therapies for IBS. That said, these biases and the difficulties of blinding diet interventions in clinical trials make it hard to do high-quality randomized controlled trials.”

In this study, Chey noted, the randomized controlled trials all carried at least a moderate risk of bias, and the cohort studies would be considered of low methodologic quality. In addition, an LF-GFD was compared to a GFD rather than a low-FODMAP diet, which could have been a more compelling comparison for IBS treatment, he said.

“The low-FODMAP diet is complex enough on its own. I worry that a combined LF-GFD would be so restrictive that it would be impractical,” he said. “There are also issues related to micronutrient deficiencies, cost, and exacerbating disordered eating behaviors or eating disorders such as avoidant/restrictive food intake disorder.”

Instead, a step-up approach that restricts only certain FODMAPs initially — such as fructans and galacto-oligosaccharides — could be more helpful, especially for patients with IBS with diarrhea, Chey and colleagues found in a recent study published in Clinical Gastroenterology and Hepatology.

“Bottom line, unless there is evidence that a LF-GFD is better than low-FODMAP alone, I would not add this diet to our list of evidence-based diets for IBS,” Chey said. “Indeed, I would argue that we should be thinking of ways to make the low-FODMAP diet simpler, not more complex.”

The study was supported by a China Postdoctoral Science Foundation grant. The authors declared no competing interests, and Chey reported no relevant disclosures. 

Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape, MDedge, and WebMD.