So do I have SIBO or not?

If your positive was methane, the label most people will still use for you is SIBO, and the organism behind the reading is not a bacterium. Both of those are true at once. It is worth knowing which one your clinician means, because the newer term exists precisely to stop the two being conflated.

Does the distinction change anything practical?

It changes what the reading is evidence of. A methane-positive result is evidence about a methanogen population, and reasoning that assumes bacteria is reasoning about a different organism. What follows clinically is a conversation with a clinician rather than something this page can hand you.

Why is the old name still everywhere?

Because it arrived first and the testing, the clinics and most of the writing were built around it. Names in medicine change slowly and unevenly, and this one is mid-change, which is why you will see both terms used for the same report.

Methane is not bacterial overgrowth

By BeatSIBO editorial team · Updated August 8, 2026

This is the most consequential piece of vocabulary in the whole subject, and it is usually mentioned once and then ignored for the rest of the article.

The organism is different

The short answer

Methane in a breath test is produced by archaea, which are a separate domain of life from bacteria. They are not unusual bacteria or a bacterial subtype. So a methane-positive result is not evidence of bacterial overgrowth, and the term intestinal methanogen overgrowth exists to say so.

Archaea and bacteria are about as closely related to each other as either is to you. Calling a methanogen population a bacterial overgrowth is not a rounding error in terminology; it names the wrong kingdom.

Why the wrong name survives

The test came first, the label came with it, and the clinics, the products and almost all the writing were built on top of that label before the distinction was widely adopted. Names in medicine change slowly, and this one is mid-change. You will see the same report called both things, sometimes by the same person.

That is worth knowing mainly so you can ask which one is meant, rather than assuming a difference in wording implies a difference in finding.

What actually follows from it

The short answer

A methane reading is evidence about a methanogen population. Any reasoning that starts from bacteria is starting from the wrong organism, however confidently it is expressed. What that means for what anyone should do is a clinical question, and it is one where the published evidence is thin enough that we will not fill the gap with a protocol.

Pimentel M et al., American Journal of Gastroenterology 2020 Clinical guideline

The guideline covering this area rates five of its six recommendations as resting on evidence its own authors grade as very low quality. That is the evidential context for the whole category and it does not improve because a page sounds certain.

What is not settled here

We are not going to tell you what to do differently on the basis of a methane result. The honest position is that the organism distinction is well established, what should follow from it is not, and those two facts are routinely blurred together by pages that use the first to sell confidence about the second.

The one thing worth taking away

If your positive was methane, and something you are reading explains your result in terms of bacteria, that page has not noticed which organism it is talking about. That is a reasonable filter to apply to everything else it says.

Common questions

So do I have SIBO or not?: If your positive was methane, the label most people will still use for you is SIBO, and the organism behind the reading is not a bacterium. Both of those are true at once. It is worth knowing which one your clinician means, because the newer term exists precisely to stop the two being conflated.
Does the distinction change anything practical?: It changes what the reading is evidence of. A methane-positive result is evidence about a methanogen population, and reasoning that assumes bacteria is reasoning about a different organism. What follows clinically is a conversation with a clinician rather than something this page can hand you.
Why is the old name still everywhere?: Because it arrived first and the testing, the clinics and most of the writing were built around it. Names in medicine change slowly and unevenly, and this one is mid-change, which is why you will see both terms used for the same report.