People who respond well to the recommended dietary therapy of restricting the intake of fermentable carbohydrates for irritable bowel syndrome, or IBS for short, have an abundance of particular types of bacteria in their gut, research published online in the newspaper Intestine.
The discovery paves the way for new treatments and better management of the disease, which affects up to 15% of people worldwide, researchers say.
The makeup of the trillions of microbes in the gut (microbiome) is thought to play a major role in the development of IBS.
It is generally recommended that you restrict fermentable carbohydrates, which are found in a wide range of foods, including wheat, onions, and milk, to relieve symptoms, an approach known as low FODMAP (oligo -, di-, mono-saccharides and fermentable polyols) diet.
But it’s not clear exactly how this diet works or if there are particular genes or molecules that will identify those in whom it will.
In an effort to fill this knowledge gap, the researchers analyzed stool samples from 56 people with IBS and 56 people who lived with them but without the disease in detail to identify the microbial profile and the genes involved. in converting food into active molecules while on their usual diet.
They then assessed the clinical response of 41 of these pairs after 4 weeks of a low-FODMAP diet by re-examining their stool samples.
Before switching to the low-FODMAP diet, analysis of stool samples from people with IBS revealed two distinct microbial “signatures”, which the researchers called “pathogenic-like” (IBSP) and “health-like” (IBSH).
The pathogenic microbial signature was abundant in Firmicutes sp, including known pathogenic bacteria, such as It’s hard, C. sordellii and C. perfringens, but very low in beneficial Bacteroidetes species.
Lactic acid bacteria Streptococcus parasanguinis and Streptococcus timonensis that are usually found in the mouth were also abundant. And bacterial genes for amino acid and carbohydrate metabolism have been overexpressed, which may explain the excess of certain metabolites linked to IBS symptoms, the researchers said.
The healthy microbial signature of the other IBS patients was similar to that found in the comparison group (household members).
After 4 weeks of the low FODMAP diet, the microbiome of the comparison group and those with a healthy microbial profile remained the same.
But the microbiome of those with the pathogenic profile has become healthier, with an increase in Bacteroidetes, and a fall Firmicutes species. And the bacterial genes involved in amino acid and carbohydrate metabolism were no longer overexpressed.
Symptoms improved in 3 of 4 patients with IBS. But the clinical response to the low-FODMAP diet was greater in people with IBS and a pathogenic microbial signature than in those with IBS and a healthy microbial signature in their gut.
“Evidence associating diet, microbiome and symptoms in [pathogenic IBS] is compelling, but studies after the introduction of candidate organisms into an animal model are needed to prove that the relationship is causal, âthe researchers cautioned.
Nonetheless, they suggest their findings could pave the way for the development of a microbial signature to identify those who would respond best to a low-FODMAP diet and better manage those who wouldn’t.
“If the bacteria represented in the [pathogenic] The subtype has been shown to play a pathogenic role in IBS, possibly through their metabolic activity, making it a target for new therapies and an intermediary [marker] to evaluate them, âthey suggest.
In a linked editorial, Professor Peter Gibson and Dr Emma Halmos of Monash University, Melbourne, describe the introduction and adoption of the FODMAP diet as “a major change in the management of patients with irritable bowel syndrome ( SCI) towards integrated care.
But if âeffective symptomatic therapy, [it’s] one that carries risks associated with the exacerbation of eating disorders, the questioning of nutritional adequacy and the presumed induction of a dysbiotic intestinal microbiota, âthey add.
They point out some limitations of the research, including the fact that FODMAP intake was improperly assessed, fiber intake, which can also influence the microbiome, was not reported, and patient discontinuation reduced power of study.
“Nevertheless, the beauty of [the study] is not in its definitive nature, but that it allows for the creation of innovative, feasible hypotheses that can be examined by targeted studies. Maybe the FODMAP diet isn’t just symptomatic therapy, âthey conclude.
Gibson, RP, et al. (2021) Two microbiota subtypes identified in irritable bowel syndrome with distinct responses to low FODMAP. Intestine. doi.org/10.1136/gutjnl-2021-326284.