SIBO Explained: Symptoms, Testing, and Meaning

Bacteria and other microbes ferment food, producing hydrogen or methane measured during breath testing.²
A clinician-guided breath test can help assess suspected SIBO before antimicrobial supplements or antibiotics are started.¹
Constipation makes methane measurement important because hydrogen-only testing can miss methane-predominant patterns.²

The test can look more certain than the condition

The odd thing about SIBO is that many people meet the term first through a home breath test graph, not through a clear medical diagnosis. The graph may show hydrogen or methane rising after drinking lactulose or glucose. That looks objective. But SIBO is not just a line on a chart. The American Gastroenterological Association says the definition still lacks perfect precision. In practice, it means symptoms, signs, or lab changes are being linked to too many bacteria, or the wrong mix of bacteria, in the small intestine.

Food is being fermented in the wrong place

Your small intestine is the long section of gut where most food absorption happens. It normally has bacteria, but not the heavy bacterial activity found farther down in the colon. In SIBO, bacteria in the small intestine ferment carbohydrates before digestion and absorption have finished. Ferment means they break down food and release gases. Hydrogen is linked more often with bloating and diarrhea. Methane is strongly linked with slower bowel movement and constipation, although methane is now often labeled intestinal methanogen overgrowth, or IMO, because the gas is made by methane producing organisms that are not technically bacteria.

This explains why symptoms can flare after meals, especially meals with fermentable carbohydrates. The issue is not that all carbohydrates are bad. The issue is location and timing. Gas is being made while food is still high in the small intestine, where stretch and pressure can feel painful.

What the breath numbers mean

Breath testing works because humans do not make hydrogen or methane gas on their own. Those gases come from gut microbes, then move into the blood, lungs, and breath. The North American Consensus uses a rise in hydrogen of 20 parts per million or more by 90 minutes during a glucose or lactulose breath test as a positive SIBO pattern. Methane of 10 parts per million or more at any point is considered methane positive.

The catch is that the drink matters. Glucose may miss overgrowth farther down the small intestine because it is absorbed early. Lactulose can reach the colon and produce a false early looking rise in some people, especially if gut contents move quickly. This is why symptoms and risk factors still matter.

The one decision that helps today

If you have bloating, abdominal pain, diarrhea, or constipation and are considering a SIBO test, choose a clinician guided glucose or lactulose breath test that measures both hydrogen and methane, instead of starting antibiotics or supplements based only on symptoms. That one choice reduces two common mistakes: treating ordinary bloating as SIBO, and missing methane linked constipation because only hydrogen was measured.

Deep dive

How it works

Bacteria in SIBO can interfere with digestion in more than one way. They ferment carbohydrates into gas, and in more severe cases they can disturb bile acids, which are substances the body uses to absorb fat. When bile acids are disrupted, stools can become greasy or loose, and fat soluble vitamin absorption can suffer. This is why weight loss, anemia, greasy stools, or nutrient deficiencies deserve medical evaluation rather than a supplement only plan.

When you'll see this

The term in the wild

You read a SIBO breath test report showing hydrogen rose from 8 ppm to 34 ppm at 75 minutes after lactulose.

That is a 26 ppm rise before 90 minutes, which meets the North American Consensus hydrogen pattern for SIBO. It still needs symptom context because lactulose can sometimes move quickly into the colon.

The number supports a discussion about treatment, but it should not be treated as a stand alone verdict.
You are constipated and your report says methane was 12 ppm at baseline, while hydrogen stayed low.

Methane at 10 ppm or more is considered methane positive. This pattern may be labeled intestinal methanogen overgrowth rather than classic hydrogen SIBO.

A hydrogen only test could miss the pattern most relevant to constipation.
You are taking a supplement blend with berberine, oregano oil, and garlic extract because an online forum called it a SIBO protocol.

Those ingredients are often marketed as antimicrobial gut support, but symptoms alone cannot tell hydrogen SIBO, methane positivity, food intolerance, constipation related bloating, or another condition apart.

Testing first can prevent weeks of harsh self treatment that may not match the actual pattern.
You have diabetes with slow stomach emptying and repeated bloating after meals, and your clinician suggests breath testing.

Conditions that slow gut movement can raise SIBO risk because bacteria have more time to grow and ferment food in the small intestine.

In this setting, testing is more meaningful than testing every episode of routine bloating.

Myths vs reality

What people get wrong

Myth

A positive SIBO breath test proves that SIBO is the only cause of symptoms.

Why people believe it The named North American Consensus cutoffs make reports look clean and decisive, even though the same document emphasizes preparation, substrate choice, and interpretation limits.

Reality

A positive pattern says gut microbes produced gas at a certain time after a test drink. It does not prove that every symptom comes from SIBO.
Myth

Methane SIBO is just another version of hydrogen SIBO.

Why people believe it Commercial reports and online forums often group hydrogen, methane, and hydrogen sulfide under the single SIBO label because it is simpler to market and discuss.

Reality

Methane points to methane producing organisms and is often tied to constipation. Many experts now use the term intestinal methanogen overgrowth, or IMO, because those organisms are not bacteria in the usual sense.
Myth

If bloating improves on a low FODMAP diet, that proves SIBO was present.

Why people believe it Diet response feels personal and convincing, so people often treat it as a diagnosis rather than a clue.

Reality

Low FODMAP eating reduces fermentable carbohydrates. That can reduce gas in several gut problems, including irritable bowel syndrome, even when SIBO is not the main issue.

A specific failure mode to avoid: do not repeat antibiotic or antimicrobial courses every time bloating returns without reassessing constipation, diet triggers, medications, and the original test quality. Recurrence can happen, but repeated treatment without a clear target can turn a gut problem into a cycle of guessing.

Frequently asked

Common questions

When should someone consider being evaluated for SIBO?

Evaluation is most reasonable when bloating, abdominal pain, diarrhea, or constipation is persistent, especially if there are risk factors such as slow gut movement, prior gut surgery, or conditions that affect intestinal movement.

Can SIBO cause nutrient problems?

Yes, more severe or long lasting cases can be linked with weight loss, greasy stools, anemia, or vitamin problems. Those signs deserve medical care rather than self treatment.

Why do some clinicians prefer glucose and others prefer lactulose?

Glucose is absorbed earlier, so it may be more specific but can miss farther down overgrowth. Lactulose travels farther, but can be harder to interpret if it reaches the colon quickly.

Should probiotics be used during SIBO treatment?

There is no one size answer. Some people feel better, some feel worse, and breath test preparation guidance has not reached a firm position on stopping probiotics before testing.

Can SIBO come back after treatment?

Yes. Recurrence can happen, especially when the reason for overgrowth, such as slow movement or an anatomic problem, has not been addressed.

Sources