SIBO vs IBS. How to tell the difference

In a 2020 review of 25 studies, breath tests found SIBO in 35.5% of people with IBS. They also found it in 29.7% of people without IBS. That small gap is the heart of the SIBO vs IBS debate.

Bloating, pain and loose stools can come from both, and the tests are far from perfect. Here is how they differ, what the tests can and cannot tell you and what to do next.

SIBO vs IBS. What is the difference?

IBS is a condition of how the gut and brain work together. SIBO means too many bacteria are living in the small intestine and causing symptoms.

• IBS is diagnosed from your symptoms, after a doctor rules out other causes. There is no single test for it.
• SIBO stands for small intestinal bacterial overgrowth. Most bacteria should live in the large intestine, further down.
• Both can cause bloating, belly pain, wind and diarrhoea. That is why they get mixed up.

The American Gastroenterological Association said in 2020 that the definition of SIBO lacks precision. It also said the role of SIBO in IBS symptoms is still debated.

How common is SIBO in people with IBS?

SIBO seems to be more common in IBS, but nobody knows the true number. It depends a lot on which test is used.

The 2020 review included 3,192 people with IBS and 3,320 people without it. People with IBS were about 3.7 times more likely to have SIBO. The authors rated the quality of the evidence as low.

A stricter test grows bacteria from fluid taken from the small intestine. With this test, SIBO showed up in 13.9% of people with IBS and 5.0% of controls. A 2026 review of 25 studies also found a strong link.

The type of IBS may matter. SIBO was more common in IBS with diarrhoea than IBS with constipation. Methane on a breath test was more common in IBS with constipation.

Can you tell SIBO and IBS apart by symptoms?

No, not reliably. Symptoms alone cannot show if you have SIBO.

A 2025 Italian study tested 564 adults who were thought to have overgrowth. Symptoms were no different in people who tested positive and people who tested negative.

Some signs make a doctor think harder about SIBO. The 2020 expert review noted that SIBO can cause greasy, pale stools in severe cases. Blood tests may show high folate or, less often, low vitamin B12. Losing weight without trying, such as 3 kg (about 7 lb) or more, also needs checking.

How is SIBO tested?

Most doctors use a breath test. You drink a sugar solution, then breathe into tubes every so often for a few hours.

A 2017 North American consensus set the rules most clinics follow.

• The sugar is either 75 g of glucose or 10 g of lactulose.
• A hydrogen rise of 20 parts per million or more within 90 minutes counts as positive for SIBO.
• Methane of 10 parts per million or more counts as methane positive. This is now often called intestinal methanogen overgrowth, and it is linked with constipation.

A 2026 Argentine consensus also advised measuring hydrogen and methane together.

Are SIBO breath tests accurate?

They are useful, but far from perfect. The two sugars give very different answers.

In the 2025 Italian study, the lactulose test found SIBO in 24.4% of people. The glucose test found it in only 4.8%. The authors felt the glucose test was more reliable.

The 2020 review saw the same pattern. Lactulose tests found SIBO 3.6 times more often than glucose tests in people with IBS.

A small 2018 US study went further. It compared glucose breath tests in 18 people with fluid taken directly from their small intestine. The breath results did not match the bacteria counts.

So a positive test does not prove SIBO, and a negative test does not always rule it out. I suggest you avoid home kits without a doctor to read the results.

How is SIBO treated?

Doctors usually treat SIBO with an antibiotic and look for any cause underneath. The 2020 expert review also stressed fixing any vitamin or nutrient gaps.

Rifaximin is the antibiotic used most. It stays mostly in the gut. A 2026 review found it cleared SIBO in 59% of people with IBS and SIBO.

Rifaximin also helps some people with IBS in general. In 2 large US trials published in 2011, people with IBS without constipation took it for 2 weeks. Adequate relief came for 40.7%, compared with 31.7% on placebo. The drug maker funded the trials.

A 2024 review found antibiotics helped 51.2% of people with IBS and SIBO, compared with 23.4% of people with IBS alone. The studies were small and of low quality. Some authors had ties to companies that make the drug and the tests.

A liquid elemental diet is another option used in specialist clinics. In a 2025 US study, 30 adults drank only a special formula for 2 weeks. Breath tests returned to normal in 73%. There was no comparison group, so this needs larger trials. Never try it without medical supervision.

Do acid-reducing medicines cause SIBO?

They might raise the risk, but the research is mixed. Stomach acid helps keep bacteria out of the small intestine.

A 2025 review of 29 studies found SIBO in 36.8% of people taking proton pump inhibitors, such as omeprazole. It was 19.9% in people not taking them. The longer people took them, the higher the risk.

The 2020 review found no such link in people with IBS. Never stop a medicine on your own. Ask your doctor if you still need it.

What does diet do for SIBO and IBS?

Diet can ease symptoms in both, but no diet has been proven to clear SIBO on its own.

The low FODMAP diet is a first-line diet for IBS. A 2026 review noted that feeling better on it does not prove it works by changing gut bacteria.

I strongly believe gut health plays a major role in nearly every health condition. SIBO vs IBS is a clear example, because both are about how gut bacteria, gut movement and the brain work together.

Try this.

• Keep a 2-week diary of food, stools, bloating and stress before you see your doctor. My IBS diet guide shows what to track.
• Bring a list of your medicines to your appointment, including acid reducers and supplements. Your doctor can check if any of them play a part.
• Do not self-treat with herbal “SIBO cleanses”. They are not well tested and may delay a real diagnosis.
• Match the plan to your stools. For loose stools, see my IBS diarrhoea diet. For hard stools, see IBS with constipation.
• Calm your nervous system. Try 5 minutes of Breathe With Me after meals.

Frequently asked questions

Can you have SIBO and IBS at the same time?

Yes. Reviews find SIBO more often in people with IBS than in people without it. Some doctors see SIBO as one possible cause of IBS symptoms in some people, while others are not convinced.

Should everyone with IBS get a SIBO test?

No. Testing helps most when your doctor has a reason to suspect SIBO. Examples are past gut surgery, signs of poor absorption or bloating that does not ease with usual care. Ask your doctor whether a test would change your treatment.

Does SIBO come back after treatment?

It can, especially if the cause underneath is not fixed. That is why doctors look at gut movement, medicines and past surgery as well as giving antibiotics.

Do probiotics help SIBO?

The evidence is too limited to say. Probiotics have been studied much more in IBS. My guide to probiotics for IBS explains which strains have evidence there.

Is methane overgrowth the same as SIBO?

Not quite. Methane comes from tiny organisms called archaea, not bacteria. It is now often called intestinal methanogen overgrowth and is linked with constipation more than diarrhoea.

What I want you to remember

SIBO and IBS share many symptoms, so you cannot tell them apart by how you feel. Breath tests help but are imperfect, and lactulose tests give many more positive results than glucose tests. Work with your doctor rather than a home kit.

Whatever the label, calm, steady habits help your gut. Learn more in the Gut Check game, and join my free 30-Day Calm Gut Challenge.