• Posted December 30, 2025

Early IBD Linked To Changes In Gut Bacteria, Evidence Shows

Early changes in a person's gut bacteria might herald the onset of inflammatory bowel disease (IBD), a new evidence review has found.

This finding could help doctors diagnose IBD earlier, and, researchers added, potentially fuel efforts to find new treatments for the condition.

Researchers found that people with the most common types of IBD, Crohn's disease and ulcerative colitis tend to lose beneficial anaerobic bacteria that help us digest complex carbohydrates. (Anaerobic means these bacteria live and grow where oxygen is not present.)

At the same time, patients experience an increase in oxygen-tolerant bacteria that are naturally found in the mouth, but have traveled to the gut.

“This is the first study to demonstrate these changes so clearly at the onset of disease — and across multiple international datasets,” co-lead researcher Dr. Peter Rimmer said in a news release. He’s a clinical lecturer in gastroenterology at the University of Birmingham in the U.K.

These results support the “oxygen hypothesis” of IBD — the idea that increased oxygen in the gut lining can disrupt a person’s microbiome, contributing to disease, researchers said.

“This research gives us a clearer picture of what’s happening in the gut at the very start of IBD,” Rimmer said. “Our findings suggest that changes in gut oxygen levels and the migration of bacteria from the mouth to the gut may play a key role in triggering inflammation — and these patterns could pave the way for earlier diagnosis and new treatments for IBD patients.”

For the new study, researchers analyzed data from more than 1,700 children and adults across 11 countries who had been recently diagnosed with IBD. 

The data was drawn from 36 previous studies.

Results specifically highlighted the presence of mouth bacterial strains like Granulicatella and Haemophilus in the guts of people with IBD.

Treating those bacteria — or preventing them from populating a person’s gut — could help ward off IBD, researchers said.

Other new treatments could focus on lowering oxygen levels in the gut, or populating the gut with healthier bacteria, the team added.

“This unique study combined significant clinical, scientific and evidence synthesis expertise to identify the unique conditions in the gut at the time of diagnosing this condition,” researcher Morris Gordon, a professor at the University of Lancashire, said in a news release. “This opens up avenues to investigate regarding screening, diagnosis and therapies.”

The study appears in the journal Gastroenterology.

More information

Johns Hopkins Medicine has more on inflammatory bowel disease.

SOURCE: University of Birmingham, news release, Dec. 23, 2025