Cutting out carbs may be key to easing irritable bowel syndrome

MELBOURNE, Australia — Eating fewer carbohydrates from all sorts of foods may be the key to relieving the symptoms of irritable bowel syndrome (IBS), a new study suggests. Researchers in Australia found that people who respond well to cutting out fermentable carbs — from pasta, potatoes, and even milk — have an abundance of bacteria in their gut.

Scientists say the findings open up the potential for new treatments for the debilitating condition that affects up to 15 percent of the world’s population. The composition and diversity of the billions of microbes in the gut – the microbiome – plays a major role in the development of IBS, researchers add. Doctors often recommend restricting fermentable carbs to ease symptoms.

Study authors call this approach the low FODMAP (fermentable oligo-, di-, mono-saccharides, and polyols) diet. However, how this diet works exactly it still unclear.

What happens to the gut when you cut carbs?

To plug this knowledge gap, a team from Monash University analyzed the stool samples of 56 people with IBS. The researchers also took stool samples from 56 people living with those participants who do not have the condition.

They were then able to identify the microbial profile and genes in converting food into active molecules while on their usual diet. Next, the team assessed the clinical response in 41 of these pairs after four weeks on the low FODMAP diet by reviewing their stool samples once more.

Before the participants with IBS started on the low FODMAP diet, samples revealed two distinct microbial “signatures,” which the researchers referred to as “pathogenic-like” (IBSP) and “health-like” (IBSH).

According to the study, the pathogenic microbial signature was abundant in harmful Firmicutes bacteria, including known disease-causing bacteria, such as C. difficile, C. sordellii, and C. perfringens.

They also uncovered the lactic acid bacteria Streptococcus parasanguinis and Streptococcus timonensis that usually appear in a person’s mouth.

The researchers report that bacterial genes for amino acid and carbohydrate metabolism were overexpressed. That may explain the excess of some metabolites that have a connection to IBS symptoms.

Better health after changing diets

The healthy microbial signature of the other IBS patients was similar to that found in the comparison group of people who lived with them but didn’t suffer from irritable bowel. After four weeks on the low FODMAP diet, the microbiome of the comparison group and those with the healthy microbial profile stayed the same.

Study authors add, however, that the microbiome of those with the pathogenic profile became healthier. They displayed an increase in Bacteroidetes and a drop in Firmicutes species. Moreover, the team did not see an overexpression of bacterial genes involved in the metabolism of amino acids and carbs.

The researchers found that the participants’ symptoms improved in three out of four patients with IBS, but the clinical response to the low FODMAP diet was greater in those with IBS and a pathogenic microbial signature than it was in those with IBS and a healthy microbial signature in their gut.

“The evidence associating diet, the microbiome and symptoms in [pathogenic IBS] is compelling, but studies following the introduction of candidate organisms into an animal model are needed to prove the relationship is causal,” the study authors write in a media release.

New probiotic treatment for IBS?

Nevertheless, the researchers feel like their findings could pave the way for the development of a microbial signature to identify those who would benefit from a low FODMAP diet and to better manage those who wouldn’t.

“If the bacteria represented in the pathogenic subtype are shown to play a pathogenic role in IBS, perhaps through their metabolic activity, this provides a target for new therapies and an intermediate marker by which to assess them,” the researchers add.

Professor Peter Gibson and Dr. Emma Halmos describe the introduction and adoption of the FODMAP diet as “a major change in the management of patients with irritable bowel syndrome (IBS) towards integrated care.”

“But while an effective symptomatic therapy, it’s one that carries risks associated with exacerbating disordered eating, challenging nutritional adequacy and putatively inducing dysbiotic gut microbiota,” they continue.

Prof. Gibson and Dr. Halmos did point out some weak parts of the study. They feel as though the study did not fully assess FODMAP intake, pointing out that participants did not report their fiber intake throughout the study period. The experts expressed that because some of the patients dropped out of the study, it reduced the power of the results.

“Nevertheless, the beauty of the study is not in its definitive nature, but that it enables the creation of feasible innovative hypotheses that can be examined by focused studies. Perhaps the FODMAP diet is not just a symptomatic therapy.”

The findings appear in the journal Gut.

South West News Service writer Georgia Lambert contributed to this report.

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