How is hydrogen-positive SIBO different from methane-positive SIBO?

Hydrogen and methane are produced exclusively by gut microbes, so an abnormal rate or quantity of gas production can indicate the presence of SIBO. The ratio of these gasses determines whether a person is predominantly a hydrogen or methane producer. When it comes to SIBO, these gasses could also provide clues to which microbes are thriving (overgrowing) in the small intestine.^[1]

While hydrogen is produced primarily by bacteria, most methane is produced by another group of microbes called Archaea, which belong to a domain of life separate from Bacteria or Eukarya (the cells that make up complex organisms, such as humans.) Archaea in the human gut consume hydrogen and carbon dioxide for energy, generating methane as a result, which is why they’re also known as methanogens.^[1]

An estimated third of healthy adults produce more methane than hydrogen, so methane hasn’t been identified as a clear cause of GI symptoms. Recent theories suggest that methane plays a role in constipation by slowing the GI system, however, and suggest differentiating between intestinal methanogen overgrowth and SIBO.^[1]

A recent meta-analysis reported that the odds of having methane-positive SIBO (possibly indicating methanogen overgrowth) were approximately two to three times higher in constipation-predominant IBS compared with diarrhea-predominant or mixed IBS, according to data from five studies.^[1]

Other research indicates that individuals with methane-positive breath tests are five times more likely to have constipation than people who primarily produce hydrogen.^[2] However, because slowing down of the GI system may support the growth of methanogens, it’s unclear which comes first: the methanogens or the constipation.^[1]