There is little research to support patients with irritable bowel syndrome (IBS) avoiding gluten or highly fermentable oligo-, di- and monosaccharides and polyols (FODMAPs), but evidence is stronger for a low-FODMAP diet than a gluten-free diet, a review found.
The systematic review and meta-analysis searched the MEDLINE, EMBASE, and Cochrane databases for randomized controlled trials of exclusion diets in IBS. A total of nine studies were determined to be eligible for the systematic review. They had to evaluate an exclusion diet versus an alternative or usual diet and assess improvement in either global IBS symptoms or abdominal pain. Results were published by the American Journal of Gastroenterology on July 26.
Two of the trials, involving 111 participants, studied gluten-free diets. Both selected patients who had responded to such a diet and then randomized them to continue the diet or have their diet spiked with gluten. Remaining on the gluten-free diet was associated with reduced global symptoms compared to spiking, but the difference was not statistically significant (relative risk [RR], 0.42; 95% CI, 0.11 to 1.55). Seven randomized trials, with 397 participants, compared a low-FODMAP diet with various control interventions. A low-FODMAP diet was associated with reduced global symptoms (RR, 0.69; 95% CI, 0.54 to 0.88). The three trials that compared low-FODMAP diets with rigorous control diets had the least heterogeneity between studies but also the least magnitude of effect.
The overall quality of the data was very low according to GRADE criteria, the study authors found. They noted that this was due to the small numbers of patients showing improvement on the intervention diets. “Specifically, there were only a total of 189 participants in the low FODMAP diet trials who experienced an improvement in their symptoms, whereas GRADE would ideally require 300 events for data to be classified as robust,” the study said. There has been an increase in the quantity and quality of trials in this area, but research is limited by lack of funding, the difficulty of blinding, and the need for long-term interventions to overcome effects of exposing the gastrointestinal tract to new foods.
“The findings of this review demonstrate that, at present, there is insufficient evidence to recommend a [gluten-free diet] to reduce global IBS symptoms” and, despite the low quality of evidence, “a low FODMAP diet currently has the greatest evidence for efficacy in IBS,” the authors said. They offered guidance on prescribing a low-FODMAP diet, which should begin with two to six weeks of excluding FODMAPs as a diagnostic test. After that, patients who did not improve should not continue the diet, while those who did should gradually reintroduce foods that contain FODMAPs to determine their sensitivities and “liberalize and personalize the low FODMAP diet with the intention of improving adherence and minimizing effects on the gut microbiome,” the authors said.