IBD and SIBO: Crohn's Disease, Ulcerative Colitis & Structural Risk

In short: SIBO is common in inflammatory bowel disease (IBD). A 2025 meta-analysis of 29 studies found it in 31% of people with IBD, about five times the odds of healthy controls². The risk is highest in Crohn’s disease, especially with strictures (narrowed bowel) or previous bowel surgery¹. SIBO causes bloating, diarrhea and pain that can look like a flare, so testing for it is worth considering when symptoms do not match the level of inflammation⁵.

This guide covers how often SIBO occurs in Crohn’s disease and ulcerative colitis, why IBD raises the risk, how to tell SIBO from a flare, and how it is treated. For an overview of SIBO and its other causes, see our causes guide.

How common is SIBO in IBD?

The studies used breath tests, so some results may be affected by the testing problems described below¹. The Indian study suggests that in some populations the extra risk is concentrated in Crohn’s disease⁷.

Why IBD raises the risk

The main risk factors are structural:

• Strictures. In Crohn’s disease, stricturing (fibrostenosing) disease raised the odds of SIBO about 7.5-fold in the 2019 meta-analysis¹. In the 2025 meta-analysis, stricturing or penetrating disease raised the odds 3.5-fold². Narrowed bowel slows the flow of contents, letting bacteria build up above the narrowing.
• Surgery. Previous bowel surgery roughly doubled the odds¹², especially removal of the ileocecal valveIleocecal valve The muscular valve where the small intestine meets the colon. It keeps colonic bacteria from flowing backward into the small intestine., the valve between the small intestine and the colon that stops colonic bacteria flowing back¹. In the German study, SIBO was more common after partial colon removal or multiple operations⁵.
• Disease in both the small and large bowel. Individual studies link combined small- and large-bowel Crohn’s disease with SIBO¹⁵.
• Slower transit. In a 2000 Italian study, people with Crohn’s disease who had had the ileocecal valve removed had a significantly slower passage of food from mouth to colon than controls⁶.

Disease activity itself does not seem to be a strong predictor. Neither the 2019 meta-analysis nor the German study found a clear link between SIBO and Crohn’s disease activity scores¹⁵.

SIBO or a flare?

SIBO and active IBD cause similar symptoms: diarrhea, bloating, abdominal pain and weight loss. In the German study, people with Crohn’s disease and SIBO had more frequent bowel movements (5.9 vs. 3.7 a day) and lower body weight than those without, and the authors warn that SIBO is often mistaken for a flare⁵. In the 2025 meta-analysis, bloating, flatulence, lower body weight, surgery and stricturing disease all predicted SIBO².

IBS-type symptoms are also common in IBD even when inflammation is controlled. A 2020 meta-analysis of 27 studies found them in about a quarter of people in endoscopic remission⁸. SIBO is one possible explanation that can be tested and treated.

Fecal calprotectin

Calprotectin is a protein released by white blood cells into the gut. A high level in stool points to active intestinal inflammation. A 2023 meta-analysis of 17 studies found it distinguished IBD from IBS with 86% sensitivity and 92% specificity⁹. SIBO itself does not seem to raise it: in a 2008 study of 40 people with SIBO, calprotectin levels did not differ from those of healthy controls¹⁰. A normal calprotectin with ongoing symptoms is therefore one situation where testing for SIBO may help. See our stool tests guide.

Breath test pitfalls in IBD

Breath tests can be harder to interpret in IBD. With fast transit, which often comes with diarrhea, lactuloseLactulose A synthetic sugar the body cannot digest or absorb. As a breath-test substrate it travels the whole small intestine, which also makes false positives more likely. can reach the colon early, where normal colonic bacteria ferment it and mimic SIBO. Glucose is absorbed in the upper small intestine, so it is less affected, but it can miss overgrowth further down³. See our breath test guide and diagnosis guide.

Treatment

SIBO in IBD is treated with antibiotics. In a 2003 Italian trial, 29 of 145 people with Crohn’s disease (20%) had SIBO. They were randomized to 10 days of metronidazole or ciprofloxacin; the breath test normalized in 13 of 15 and 14 of 14 respectively, and bloating improved in more than 80%⁴. The 2025 meta-analysis also concluded that antibiotic treatment may be effective for SIBO in IBD². RifaximinRifaximin An antibiotic that is barely absorbed into the bloodstream, so it acts mainly inside the gut. It is a common prescription treatment for SIBO. is the most studied antibiotic for SIBO in general; see our antibiotics guide.

Because strictures and surgery are the main drivers, SIBO can return in people with structural Crohn’s disease. Managing the underlying disease with your IBD team, including treatment of strictures, matters for preventing relapse. See our guide to preventing relapse.

Common questions

Can SIBO cause IBD?

There is no evidence that it does. SIBO is more common in IBD mainly because of strictures, surgery and changes in gut movement¹².

Is SIBO more common in Crohn’s disease or ulcerative colitis?

Crohn’s disease, especially with strictures or after surgery. In the 2025 meta-analysis, the rates were 32% and 28%², but in some studies the risk in ulcerative colitis was close to that of healthy people⁷.

Should I be tested for SIBO if I have IBD?

Ask your IBD team if you have bloating, diarrhea or pain that seems out of proportion to your inflammation, particularly with strictures or previous surgery⁵.