Distinct gut microbes and metabolites underlie differences in irritable bowel syndrome

Giorgia Guglielmi

09.01.2026

Researchers have found that certain gut bacteria and their metabolites differ between IBS subtypes.

What is already known

Irritable bowel syndrome (IBS) is a common condition that causes symptoms such as bloating, diarrhea, and constipation, but symptoms can vary widely between people. People with IBS often have altered gut microbiotas, but how specific bacteria differ between IBS subtypes and how they relate to symptoms remained largely unexplored.

What this research adds

Researchers analyzed stool samples from people with IBS and found that people with diarrhea-predominant IBS had reduced microbial diversity, higher metabolic activity, and fewer butyrate-producing bacteria, with species such as Ruminococcus gnavus, Dorea species, and Bifidobacterium pseudocatenulatum driving changes. Instead, people with constipation-predominant IBS showed distinct patterns, including increased propionate production linked to Prevotella copri. However, some microbes were shared across IBS subtypes, suggesting common gut-brain mechanisms.

Conclusions

The findings suggest that specific gut bacteria shape metabolism and influence IBS symptoms.

Irritable bowel syndrome (IBS) is a common condition that causes symptoms such as bloating, diarrhea, and constipation, but symptoms can vary widely between people. Now, researchers have found that certain gut bacteria and their metabolites differ between IBS subtypes.

The findings, published in Scientific Reports, suggest that specific microbes shape metabolism and influence IBS symptoms.

Previous research has shown that people with IBS often have altered gut microbiotas, but how specific bacteria differ between IBS subtypes and how they relate to symptoms remained largely unexplored.

To understand these differences, Andrea Shin at the University of California Los Angeles and her colleagues set out to analyze stool samples from people with IBS and healthy volunteers.

IBS subtypes

The researchers profiled the participants’ gut microbiotas and measured the levels of short-chain fatty acids (SCFAs) in the stool samples. SCFAs, produced by gut bacteria, are known to influence digestion and gut health.

People with diarrhea-predominant IBS had reduced microbial diversity but higher metabolic activity, with fewer bacteria capable of producing butyrate—a beneficial SCFA. Key bacterial species—including Ruminococcus gnavus, Dorea species, and Bifidobacterium pseudocatenulatum—appeared to be major SCFA producers and were associated with diarrhea-predominant symptoms.

Instead, people with constipation-predominant IBS showed distinct patterns. Bacteria such as Prevotella copri and Akkermansia were linked to increased levels of the SCFA propionate, which may influence constipation. However, some bacterial species, including Ruminococcus torques and Clostridium comes, were shared across IBS subtypes, suggesting common gut-brain mechanisms.

Impaired metabolism

Further analyses revealed that differences in microbial metabolism affect how carbohydrates and mucin—a component of the gut lining—are broken down. These changes appear to influence stool form and bowel function, providing a link between microbial activity and IBS symptoms.

In people with diarrhea-predominant IBS who also had problems in reabsorbing bile acids, the team found reduced abundances of SCFA-producing bacteria, suggesting that impaired microbial metabolism could worsen their symptoms.

“Our findings support the utility of a paired microbe-metabolite approach as a viable strategy for identifying functionally relevant microbial features in heterogenous IBS patient populations,” the authors say.