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.