SIBO and endometriosis: what a 2025 study found

The study in short

Researchers analysed 1,027 women who had taken a lactulose breath test during a healthcare check-up between November 2021 and June 2023. From this group, 148 women with endometriosis — confirmed by MRI or histology — were each matched with a woman of the exact same age without endometriosis. Both groups were then compared on breath test results and digestive symptoms.

Key findings

Women with endometriosis also showed significantly more altered gut transit (85.8% vs 71%) and more dizziness (44.8% vs 28.7%). The type of overgrowth mattered too: hydrogen-dominant SIBO was linked to a higher risk of diarrhoea, while methane overgrowth (IMO) was linked to a higher risk of acid reflux.

Why this matters

Digestive complaints in endometriosis are often attributed to the endometriosis itself — "it's just part of it." This study suggests something more specific may be going on: an overgrowth of bacteria or methane-producing archaea in the small intestine that can be identified with a simple, non-invasive breath test. The authors conclude that abnormal digestive overgrowth should be assessed in all endometriosis cases, as this could open up a new avenue of supportive care.

What this means for you

If you have endometriosis and struggle with bloating, constipation, reflux or unpredictable stools, it is worth considering whether SIBO or IMO plays a role. A lactulose breath test — the same type used in this study — can show whether an overgrowth is present and which gas pattern dominates. That distinction guides the next steps, because hydrogen- and methane-dominant overgrowth are approached differently.

Note: this was a case-control study showing an association, not proof that SIBO causes endometriosis symptoms. Testing and any follow-up should always be discussed with your physician, especially when endometriosis is involved.