Microbiota May Predict Success on Low FODMAP Diet

Heidi Splete

December 15, 2021

Two distinct gut microbiota subtypes showed an enhanced clinical response to a low FODMAP diet in an analysis of 41 adults with irritable bowel syndrome and household controls.

Irritable bowel syndrome (IBS) has a significant impact on quality of life, and some patients find relief on a low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) diet, wrote Kevin Vervier, PhD, of Wellcome Sanger Institute, Hinxton, England, and colleagues. However, the mechanism of action for the success of low FODMAP diets remains unclear, the diet is hard for many patients to follow, and the long-term impact on health is unknown. Therefore, research is needed to identify patients who would derive the most benefit, they said.

In a study published in Gut, the researchers used metagenomics and functional analysis to identify potential biomarkers of response to a low FODMAP diet. They analyzed stool samples from 41 pairs of IBS patients and household contacts. Stool samples were collected at baseline while on usual diets, and again after 4 weeks and 12 weeks on a low FODMAP diet. The patients were divided into two groups based on microbiota clusters; baseline demographics and clinical characteristics were similar between the clusters. In addition, symptom severity was measured using the IBS Severity Scoring System (IBS-SSS).

Cluster 1 was referred to as IBSP microbiome type because of its pathogenic properties, and cluster 2 as IBSH microbiome type because of its resemblance to the microbiome of healthy household controls, the researchers wrote.

"We found a significant enrichment of 109 functional pathways and significant depletion of 13 functional pathways in IBSP microbiomes compared with IBSH microbiomes," the researchers said.

More specifically, the IBSP microbiomes were enriched in Firmicutes and in genes for amino acid and carbohydrate metabolism, at baseline, while the IBSH microbiomes were similar to healthy controls.

After 4 weeks on the low FODMAP diet, the IBSP microbiomes normalized, with increased levels of Bacterioides and decreased levels of pathobionts (including Clostridium difficile, Streptococcus parasanguinis, and Paeniclostridium sordellii) to create a microbiome profile resembling the IBSH microbiomes and healthy controls. The taxonomic profile of microbiomes observed in IBSH and healthy controls did not demonstrate a significant shift.

Although both microbiome groups showed improvement in IBS-SSS scores from baseline on the low FODMAP diet, decreasing from a mean baseline score of 278 to a diet score of 128, the improvement was greater in the IBSP group than the IBSH group (delta, 194 vs. 114, respectively; P = .02), the researchers noted. "The shift in the IBSP microbiota to a healthy profile appeared stable for at least 3 months and correlated with continuing symptomatic well-being," they wrote.

The distinct responses of the IBSP and IBSH microbiomes to the low FODMAP diet suggest a potential mode of action, the researchers said in their discussion. Based on their findings, "it is possible that removal of the eliciting dietary component starves the pathobionts, leading to reduction in their growth and metabolism and a consequent decrease in symptoms, accompanied by an expansion of commensal or symbiotic species leading to a health-associated microbiome," but more research is needed to prove causality, they said.

The study findings were limited by several factors, including the relatively small sample size, strict inclusion criteria, restriction of medications, and need for participation by household controls, the researchers noted. Other limitations include the inability to control for other factors that could have impacted the gut microbiota, such as the placebo effect and psychological factors, they said.

However, the findings provide a foundation for more research and should be validated in other populations involving different geographical regions and dietary habits, they said. "The identification of a microbial signature 'biomarker' that correlates with improved response to a low FODMAP diet may, if validated, allow better stratification and selection of patients likely to benefit from the diet," they concluded.

Setting the Stage for Focused Studies

The low FODMAP diet has demonstrated effectiveness for symptom relief in IBS, although potential risks include exacerbation of disordered eating, nutrition deficiencies, and disrupting gut microbiota, wrote Peter R. Gibson, MD, and Emma P. Halmos, MD, of Monash University and Alfred Health, Melbourne, in an accompanying editorial. However, the current study takes a new step on the journey to identifying patients most likely to respond to a low FODMAP diet, they said.

The editorialists noted three key takeaway points. First, the fecal microbiome may predict response to a low FODMAP diet. Second, the correction of the microbiome through the low FODMAP diet appeared to continue even after the diet was discontinued. "The other intriguing finding was that trehalose metabolic pathways were 'activated' in those with dysbiosis," suggesting that trehalose might be an unrecognized FODMAP, the researchers noted. Trehalose has not been well studied but has been associated with pathogenicity, they said.

Although the study may overemphasize the impact of the low FODMAP diet given the relatively poor assessment of FODMAP intake, "the beauty of Vervier's work is not in its definitive nature but in that it enables the creation of feasible innovative hypotheses that can be examined by focused studies," they concluded.

The current study is important because IBS and related disorders of gut-brain interaction are common and greatly impact the quality of life of affected individuals, Jatin Roper, MD, of Duke University in Durham, N.C., said in an interview. Although the mechanisms for improvement are unknown, he said, "The low FODMAP diet is widely used to treat IBS, based on the hypothesis that this diet modifies the gut microbiome in a beneficial way."

The study authors made two important discoveries, said Roper. "First, they found that they were able to distinguish IBS versus household controls based on their gut microbial signatures as well expression of key metabolic genes," he said. "Second, they identified a unique microbiota subtype that was associated with a significant clinical response to the low FODMAP diet in IBS patients; IBS patients with a 'pathogenic' microbiome consisting of high Firmicutes and low Bacteroidetes responded to a greater degree to the low FODMAP diet compared to IBS patients with a 'healthy' microbiome that was similar to controls," he explained. "Furthermore, after time on the low FODMAP diet, the IBS patients with pathogenic microbiome signatures developed a microbiome with low Firmicutes and high Bacteroidetes, which is thought to be healthy," he added.

"These findings are exciting because they suggest that a patient's microbial signature might be used clinically to predict response to the low FODMAP diet," said Roper. "The surprising aspect of these results is that the microbial signature alone was able to predict response to a low FODMAP diet, despite the complex effects of the diet on host physiology and metabolism and the multifactorial etiology of IBS," he noted.

However, larger clinical studies are needed to confirm the study findings results in larger patient cohorts and to show that standardized clinical assays can be used to prospectively predict response to dietary interventions such as low FODMAP in IBS, Roper emphasized.

"This paper provides preliminary and provocative findings that suggest that gut microbiota metabolites may play a role in the pathogenesis of IBS," said Roper. "Future basic science and translational research is needed to study the mechanisms by which specific bacterial metabolites regulate intestinal function and disorders such as IBS. I hope that this research will eventually lead to metabolite-based therapies for IBS and other gastrointestinal disorders," he said.

The study received no outside funding. Lead author Vervier had no financial conflicts to disclose. Gibson disclosed authoring two educational/recipe books on the low FODMAP diet, and Monash University financially benefits from the sales of a digital application, booklets, and online courses on the low FODMAP diet. Halmos had no financial conflicts to disclose. Roper had no financial conflicts to disclose.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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