A low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) diet is often recommended to reduce IBS symptoms.
"Our research has shed light on how the makeup of the gut microbiome impacts on symptoms of IBS, and how diet can be used as a useful tool in some cases to help treat this common and often debilitating condition," Dr. Kevin Vervier of the Wellcome Sanger Institute in Hixton told Reuters Health by email.
"It is exciting to see that in about half of IBS patients there is a microbiome profile that can be changed dramatically by following the low FODMAP diet," he said. "In addition, it's encouraging that 75% of all the people studied reported improvements in their symptoms following the diet, even if they had a more 'healthy' microbiome profile to start with."
As reported in Gut, Dr. Vervier and colleagues used metagenomics to analyze stool samples from 56 people with IBS and 56 household controls, all of whom followed their usual diet.
The team also studied microbiota changes in 41 of the pairs after four weeks on a low FODMAP diet.
Analyses of stool samples before the low FODMAP diet revealed two distinct microbiota profiles: IBSP (pathogenic-like) and IBSH (health-like).
The pathogenic microbial signature was abundant in a broad range of Firmicutes species, including known human pathogens such as C. difficile, C. sordelli and C. perfringens, as well as in pathobionts such as Faecalicatena gnavus; however, IBSP low in Bacteroidetes species associated with the guts of healthy adults.
By contrast, the healthy IBS microbiomes were similar to those of controls.
On the low FODMAP diet, IBSH and control microbiota were unaffected, but the IBSP signature shifted towards a health-associated microbiome, with an increase in Bacteroidetes, a decrease in pathogenic Firmicutes species, and the normalization of previously overexpressed genes for amino acid and carbohydrate metabolism.
As Dr. Vervier noted, three out of four patients experienced improvement in symptoms on the low FODMAP diet, but the response was greater in those with IBSP.
The authors conclude, "The effectiveness of FODMAP reduction in IBSP may result from the alterations in gut microbiota and metabolites produced. Microbiota signatures could be useful as biomarkers to guide IBS treatment; and investigating IBSP species and metabolic pathways might yield insights regarding IBS pathogenic mechanisms."
Dr. Vervier added, "Further research can delve deeper into the exact bacteria involved, which could be targeted for treatments, and help uncover what causes the development of IBS. For now, it is encouraging to see the impact that the low FODMAP diet can have on the improvement of symptoms in the majority of those living with IBS."
Dr. Peter Gibson of Monash University, coauthor of a related editorial, commented in an email to Reuters Health, "This study has provided potential explanations (at least in part) for the individual variation in responses to the initial strict reduction in FODMAP intake - depends upon whether the individual has an aberrant pattern and metabolic activity of the gut microbiota (dysbiosis) - and why those with good responses can have continuing symptomatic benefit with only relatively minor dietary restriction - i.e., the strict phase leads to correction of the dysbiosis."
SOURCE: https://bit.ly/3I4gfqc and https://bit.ly/314BZSd Gut, online November 22, 2021.
By Marilynn Larkin
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