Composition of the Intestinal Microbiota of Patients with IBS May Predetermine the Success of a Diet with Low Fermentable Carbohydrates

Patient Nutrition and IBS Symptoms

For some patients with irritable bowel syndrome (IBS), excluding foods containing fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) from their diet is clinically beneficial. However, not all patients respond to this diet, and adhering to it can be quite demanding, often requiring more time for meal preparation. The long-term health effects of following this diet are also unknown. Therefore, it is necessary to better understand the mechanism of its functionality and ideally identify prognostic biomarkers to determine which patients may benefit from this intervention.

The intestinal microbiome is believed to be a key etiological factor in the development of IBS. Recent clinical studies suggest that IBS patients have a reduced content of the Bacteroidetes strain compared to healthy controls. To identify the influence of diet on the composition of the intestinal microbiota, detailed taxonomic profiling and quantification of the represented species are needed. This is precisely what the authors of the presented study focused on.

Study Methodology

This prospective single-center study included 56 adult patients with IBS dominated by diarrhea (IBS-D) or alternating diarrhea and constipation (IBS-M), accompanied by a control individual living in the same household for each patient. Participants underwent metagenomic analysis of the intestinal microbiota from stool samples. Clinical response and changes in the intestinal microbiota were assessed in 41 pairs of participants after 4 weeks of adhering to a low-FODMAP diet.

Results

Baseline metagenomic profile analysis of IBS patients revealed two distinct microbial profiles - pathogenic (IBS^P) and resembling healthy controls (IBS^H). The IBS^P profile contained a larger amount of Firmicutes bacteria and genes for amino acid and carbohydrate metabolism, and a smaller amount of Bacteroidetes bacteria.

After the period of following a low-FODMAP diet, there was no change in the microbiota of patients with the IBS^H profile or healthy controls. In contrast, patients with the IBS^P profile showed a shift towards a profile associated with a healthy microbiota - a decrease in the Firmicutes strain (p = 0.004), an increase in the Bacteroidetes strain (p = 0.009), and normalization of primary metabolic gene levels. Clinical response to the low-FODMAP diet was higher in the IBS^P group compared to the IBS^H group.

Conclusion

Approximately half of the enrolled IBS patients had a 'pathogenic' intestinal microbiota profile that shifted towards a 'healthy' profile when following a low-FODMAP diet. The effectiveness of this diet may, therefore, be the result of changes in the intestinal microbiota and the representation of the metabolites it produces.

The intestinal microbiota can also be supported with products containing natural substances with beneficial effects on the intestinal mucosa. According to a recent study, an increase in the Bacteroidetes strain was observed in IBS patients who clinically responded to the administration of Aloe vera extract (n = 10).

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Sources:
1. Vervier K., Moss S., Kumar N. et al. Two microbiota subtypes identified in irritable bowel syndrome with distinct responses to the low FODMAP diet. Gut 2021 Nov 22: gutjnl-2021-325177, doi: 10.1136/gutjnl-2021-325177 [Epub ahead of print].
2. Ahluwalia B., Magnusson M. K., Böhn L., et al. Randomized clinical trial: effects of Aloe barbadensis Mill. extract on symptoms, fecal microbiota and fecal metabolite profiles in patients with irritable bowel syndrome. Neurogastroenterol Motil 2020; 32 (8): e13860, doi: 10.1111/nmo.13860.