Irritable Bowel Syndrome: Little Evidence for FODMAP Diet

Yael Waknine

August 14, 2015

There is "very limited evidence" to support a diet low in short-chain carbohydrates, also known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols), for patients with irritable bowel syndrome (IBS), according to a review published online August 6 in the Drug and Therapeutics Bulletin.

"Evidence for the efficacy of the low FODMAP diet to improve symptoms of [IBS] is based on a few relatively small, short-term unblinded or single-blinded controlled trials of varying duration," write James Cave, OBE, FRCGP, editor-in-chief of the Drug and Therapeutics Bulletin, and colleagues, noting that improper use could lead to dietary insufficiencies.

Developed in Australia, the FODMAP diet is based on the premise that patients with IBS have a limited ability to process the small-chain carbohydrates found in wheat, onions, legumes, milk, high-fructose corn syrup, and artificial sweeteners. FODMAP fermentation in the large intestine results in luminal distension, causing pain, bloating, and changes in motility.

Two recent review articles had conflicting conclusions: one concluded there is high-quality evidence supporting the efficacy of low FODMAP diet for IBS, whereas the other "was more cautious in its conclusion," report Dr Cave and colleagues.

In an effort to achieve consensus, researchers evaluated some of the same data but also included a 6-week study of 123 patients randomly assigned to a low FODMAP diet, Lactobacillus supplementation, or a regular Danish diet. Results revealed that both interventions yielded clinically significant symptom improvement, as evaluated using the 101-point IBS severity scoring system. Notably, 15 participants dropped out of the study, citing difficulties in dietary adherence.

The other studies also reported some level of symptom improvement, albeit with considerable variations in what was tested and how. One found that the median time to symptom resolution was 3.5 weeks; another concluded that breath-test evidence of fructose malabsorption "had no bearing on the benefit."

Because none of the randomized controlled studies exceeded 6 weeks' duration, the long-term effect of the FODMAP diet remains unknown. Restrictive or exclusion diets do carry a risk for nutritional inadequacy or harmful changes to the gut microbiota, the authors write. One study found a reduction in beneficial bifidobacteria, but further evaluation is needed to determine whether the effect is temporary or permanent.

"Some guidelines suggest that a low FODMAP diet may be appropriate for motivated patients for whom other therapies have not offered sufficient symptomatic relief; and that advice on a low FODMAP diet should be provided by a dietician with specialist knowledge of this type of intervention," the researchers state. "However, we believe that patients should be advised that there is very limited evidence for its use, the ideal duration of treatment has not been assessed in a clinical trial and its place in the management of IBS has not been fully established."

A Treatment Option

In an interview with Medscape Medical News, David Johnson, MD, MACG, FASGE, professor of medicine and chief of gastroenterology at Eastern Virginia Medical School in Norfolk, expressed his support of the FODMAP diet as an option in IBS.

"[The FODMAP diet] is worth a shot. It may help patients feel better, and they don't have to take an expensive medication or get approval from insurance. I tell patients to try it for 2 to 4 weeks; they can tell pretty quickly if something is affecting them," Dr Johnson said.

"There are a number of reports where the FODMAP diet has been used successfully in patients with IBS. Most gastroenterologists would accept that it has good scientific rationale with a relatively weak base of evidence," he added, noting the difficulties of controlling for other variables in this type of study.

"It's important not to throw the concept out just because of a lack of strong evidence. In some of my patients, [the FODMAP diet] has been very beneficial," he concluded.

The authors and Dr Johnson have disclosed no relevant financial relationships. Dr Johnson is an advisory board member for Medscape.

Drug Therapeutics Bull. Published online August 6, 2015. Abstract

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