Endometriosis and SIBO: Understanding the Gut Connection

If you live with endometriosis, you probably know the bloating, the cramps and the unpredictable bowel changes all too well. For many women, these gut symptoms feel just as disruptive as the pelvic pain. New research is now shining a light on why. A growing body of evidence links endometriosis and SIBO — small intestinal bacterial overgrowth — and suggests the two may be more connected than we once thought. Below, we look at what the latest study found, why the gut and endometriosis may be intertwined, and what you can do to feel better.

Key takeaways

• Gut symptoms are common in endometriosis. Bloating, constipation and abdominal pain often go hand in hand with it.
• A 2025 case–control study found bacterial or methanogen overgrowth in around 92% of women with endometriosis, compared with 83% of women without it (1).
• Intestinal methanogen overgrowth (IMO) was the most common pattern, and it was linked to more constipation and reflux.
• The two conditions are strongly linked, though the reasons — and the true size of the gap between groups — are still being worked out. Slower gut movement, inflammation, scar tissue and oestrogen metabolism may all play a part.
• Association is not the same as cause. Even so, it is a good reason to look closely at the gut when endometriosis symptoms are stubborn.

What is endometriosis, and why does it affect the gut?

Endometriosis can affect the gut directly, because the same tissue that causes pelvic pain can also grow on the bowel and bladder, not just inside the pelvis (2). Endometriosis is a long-term condition where tissue similar to the lining of the womb grows in other parts of the body. It is common, affecting up to 1 in 10 women and those assigned female at birth (3).

The most familiar symptoms are pelvic pain, painful or heavy periods, and pain during sex. But because the bowel can be directly involved, digestive symptoms are common too: gut symptoms affect most women with endometriosis, and bloating is one of the most frequently reported (9).

Endometriosis is a condition that is managed rather than removed entirely. Treatment usually focuses on easing symptoms and improving quality of life (2). Understanding the gut is part of that wider picture.

What are SIBO and IMO?

SIBO (small intestinal bacterial overgrowth) is a build-up of bacteria in the small intestine, where numbers are normally kept low. IMO (intestinal methanogen overgrowth) is a related but distinct pattern, where methane-producing microbes — rather than typical bacteria — dominate the overgrowth. Both are usually identified with the same non-invasive test: a hydrogen and methane breath test (4).

When too many microbes gather in the small intestine, they ferment food early and produce gas. The result can be bloating, wind, abdominal pain, and either diarrhoea or constipation (4). Methane tends to slow the gut, so IMO in particular is closely associated with constipation (4).

Your gut has a built-in cleaning system that helps prevent this build-up. Between meals, a wave of muscle activity called the migrating motor complex sweeps leftover food and bacteria along the small intestine. When this wave slows down, bacteria have more chance to accumulate (4).

What did the new study find about endometriosis and SIBO?

Overgrowth was detected in 91.9% of women with endometriosis, compared with 83.1% of women without it — a statistically significant difference (1). The study, a 2025 case–control study, compared 148 women with confirmed endometriosis against 148 women of the same age without it, and everyone completed a lactulose breath test (1).

The endometriosis group also had more digestive trouble overall:

Methane-type overgrowth was the most common pattern, making up around 63% of positive results. Hydrogen-type SIBO was linked to a higher chance of diarrhoea, while IMO was linked to acid reflux (1).

The authors concluded that overgrowth is worth assessing in women with endometriosis, as it could open up a new avenue for support (1).

It is worth reading these numbers carefully, though. This is a single study, and it shows an association rather than proof of cause. It also cannot tell us which came first. And notice that even the comparison group tested positive 83% of the time. That is very high, and it reflects a known limitation of lactulose breath testing, which can over-call overgrowth. So the headline figure deserves a little caution. The gap between the two groups was still real and clinically interesting, but it is one piece of a developing picture, not the final word.

Why might endometriosis and SIBO be connected?

There is no single agreed explanation yet. Several plausible threads are being explored, and they may well overlap.

Does slower gut movement play a role?

Slower gut movement is one of the best-recognised setups for bacterial overgrowth, which makes it a strong candidate for the endometriosis–SIBO link (4). Endometriosis involves ongoing inflammation and can create adhesions — bands of scar tissue that sometimes involve the bowel (2). Anything that disturbs the small intestine’s normal cleaning wave, the migrating motor complex described above, can allow bacteria to build up (4).

Could inflammation and the gut barrier be involved?

One theory is that inflammation makes the gut barrier more permeable, letting bacteria and their by-products cross more easily and add to the whole-body inflammation seen in endometriosis (6). Endometriosis is increasingly understood as a whole-body inflammatory condition, not just a pelvic one, and research suggests an imbalanced gut microbiome may feed into that inflammatory environment (6). This is a plausible thread rather than a proven mechanism.

What about oestrogen and the “estrobolome”?

Endometriosis is an oestrogen-driven condition. Interestingly, certain gut bacteria help regulate how oestrogen is recycled in the body, through an enzyme called beta-glucuronidase. This collection of oestrogen-handling microbes is known as the estrobolome. When it is out of balance, more oestrogen may be reabsorbed into circulation, which could favour endometriosis (5). This is a two-way relationship: hormones shape the microbiome, and the microbiome shapes hormones. For now, this remains a promising idea rather than settled science (5).

How can you tell “endo belly” from SIBO bloating?

Many women with endometriosis describe a sudden, severe bloating known as “endo belly” (9). It can look and feel very similar to the bloating of SIBO, which makes the two hard to separate. There are some useful differences, though.

These are not mutually exclusive, and symptoms overlap closely with irritable bowel syndrome (IBS) too — doctors increasingly look at endometriosis, IBS and SIBO/IMO together rather than in isolation (7). A woman can have endo belly and SIBO at once, and the 2025 Halfon et al. study above suggests that overlap is common (1). Rather than guessing, testing can help you understand what is actually going on.

What can you do if you have endometriosis and gut symptoms?

Here is where to start, working alongside your medical care rather than instead of it:

• Get the full picture first. Endometriosis needs a medical diagnosis, so it is important to work with your GP or gynaecologist rather than self-diagnosing (2). Gut testing sits alongside that, not instead of it.
• Consider breath testing. If digestive symptoms are prominent or persistent, a breath test can help identify hydrogen-type SIBO or methane-type IMO (4). Healthpath’s SIBO Plan uses a simple home breath test, with your results reviewed by a practitioner so you know what they mean and what to do next.
• Look at the wider microbiome. When symptoms are complex, it can help to understand the bigger gut environment as well. Healthpath’s Ultimate Gut Health Test combines advanced stool testing with a practitioner-led review and a personalised food, lifestyle and supplement plan.
• Ask about treating any overgrowth directly. If testing confirms SIBO or IMO, treatment guidelines typically involve a course of a gut-targeted antibiotic such as rifaximin, or in some cases herbal antimicrobials, followed by strategies to reduce relapse — for example, prokinetics that support the migrating motor complex between meals (4). This is best guided by a practitioner, since the right approach depends on which type of overgrowth is present. There are additional considerations such as probiotics and prebiotics too. Check out our deep dive article on treating SIBO for a more detailed exploration,
• Explore a low FODMAP approach. The low FODMAP diet has some of the strongest evidence for easing gut symptoms in endometriosis. In one study, 72% of women with both endometriosis and IBS reported a significant improvement in bowel symptoms after four weeks (7). A 2025 randomised controlled trial found that 60% of women with endometriosis responded to a low FODMAP diet, compared with 26% on a control diet (8). It works best as a short-term learning tool, with foods reintroduced afterwards, ideally with support.

These steps may ease symptoms and support your digestion. They do not remove endometriosis itself, and everyone is different, which is why a personalised, practitioner-led approach tends to work best.

Frequently asked questions

Does SIBO cause endometriosis? There is no evidence that it does. The research shows the two often occur together, but it does not show that one causes the other, or which comes first.

Can addressing SIBO help my endometriosis symptoms? It may ease gut symptoms such as bloating and irregular bowel habits, which can make a real difference to daily life. It will not remove the endometriosis. It is best explored with a practitioner as part of a wider plan.

Should everyone with endometriosis be tested for SIBO? Not necessarily. But if your gut symptoms are prominent, or they have not settled despite other measures, testing is a reasonable and informative next step.

Is the low FODMAP diet safe to follow long term? It is designed as a short-term diagnostic tool, not a permanent way of eating. Staying on it too long can affect your microbiome, so foods are gradually reintroduced, ideally with a qualified practitioner guiding you.

This article is for information only and is not intended to diagnose, treat, cure or prevent any disease. Always speak to your GP or a qualified healthcare professional about your individual symptoms.

Scientific references

1. Halfon et al. High prevalence of small intestinal bacterial overgrowth and intestinal methanogen overgrowth in endometriosis patients: A case–control study. International Journal of Gynecology & Obstetrics. 2025;170:284–291.
2. NHS. Endometriosis.
3. Royal College of Obstetricians and Gynaecologists (RCOG). Endometriosis.
4. Pimentel M, Saad RJ, Long MD, Rao SSC. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. American Journal of Gastroenterology. 2020;115:165–178.
5. Could the estrobolome have a role in endometriosis pathogenesis and infertility? A systematic review. BMC Women’s Health. 2025.
6. The Multifactorial Pathogenesis of Endometriosis: A Narrative Review Integrating Hormonal, Immune, and Microbiome Aspects. 2025.
7. Moore JS, Gibson PR, Perry RE, Burgell RE. Endometriosis in patients with irritable bowel syndrome: Specific symptomatic and demographic profile, and response to the low FODMAP diet. Australian and New Zealand Journal of Obstetrics and Gynaecology. 2017;57:201–205.
8. Varney JE et al. Effect of a 28-Day Low FODMAP Diet on Gastrointestinal Symptoms Associated With Endometriosis (EndoFOD): A Randomised, Controlled Crossover Feeding Study. Alimentary Pharmacology & Therapeutics. 2025.
9. Endo Belly: What Is It and Why Does It Happen? — A Narrative Review. 2023.