Spotlight on FODMAPs

Two studies published this month, a review and a randomized, placebo-controlled trial, looked at the impact of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) in patients with irritable bowel syndrome.

Two studies this month focused on the impact of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) in patients with irritable bowel syndrome (IBS).

First, a review of the efficacy and potential harms of the low-FODMAP diet, which was published online on June 7 by Gut, found that “convincing evidence exists” for the diet's clinical efficacy in patients with IBS.

Most clinical trials of the diet to date have assessed short-term clinical endpoints, and the available evidence suggests that 50% to 80% of patients with IBS report improved symptoms on a low-FODMAP diet in the short term (12 or fewer weeks). Further, data from comparative trials suggest the diet is as effective as general dietary and lifestyle interventions.

Although limited data are available from long-term clinical trials, a retrospective study found that a FODMAP-modified diet produced clinical benefit in 57% to 74% of patients at 14 to 16 months, although the results are likely subject to substantial recall bias, according to the review.

Some trials have reported potential hazards of the diet, such as its effect on gut microbiota. In particular, it leads to lower intake of prebiotic fructans and galacto-oligosaccharides (and therefore a reduction in substrate available for colonic fermentation), the review stated. Studies have also found marked reductions in the abundance of stool Bifidobacterium in individuals who reduced FODMAP intake by 50% compared with controls who maintained their usual diets. The review authors noted that reintroducing FODMAPs into the diet as tolerated may attenuate some of these potentially unfavorable changes. Another potential approach is supplementing with probiotics or prebiotics, they added.

The second study, a placebo-controlled trial that had two authors in common with the review, addressed both the diet's efficacy and its effects on the microbiome. Researchers randomized 104 patients with IBS (ages 18 to 65 years) to receive one of the following interventions for four weeks: low-FODMAP diet and placebo (n=24), low-FODMAP diet and probiotic (n=27), sham diet and placebo (n=27), or sham diet and probiotic (n=26). Primary endpoints were adequate relief of IBS symptoms and abundance of stool Bifidobacterium species. Results were published online on June 15 by Gastroenterology.

There was no significant interaction between the interventions in adequate relief of symptoms or difference in Bifidobacterium species. In an intention-to-treat analysis, a higher proportion of patients on the low-FODMAP diet versus the sham diet had adequate symptom relief (57% vs. 38%), although the difference was not statistically significant (P=0.051). Similar results reached significance in a per-protocol analysis of 87 participants (61% vs. 39%; P=0.043).

At follow-up, abundance of stool Bifidobacterium species was lower in patients on the low-FODMAP diet (8.8 rRNA genes/g) than in those on the sham diet (9.2 rRNA genes/g; P=0.008). However, abundance of the species was higher in patients given a probiotic (9.1 rRNA genes/g) than those given placebo (8.8 rRNA genes/g; P=0.019).

“Given the lack of interaction between diet and probiotic interventions in this study, the effects of each can be considered additive,” the study authors wrote. “We have therefore shown that the low FODMAP diet-induced reduction in Bifidobacterium can be modified with the addition of a specific bifidobacteria-containing probiotic.”

Limitations of the trial include the difficulty of maintaining blinding and the exclusion of patients with constipation-predominant IBS. It is also unclear whether symptom response was due to collective restriction of FODMAPs or due to remove of individual FODMAPs.