IMO: Too much methane gas in the gut
Content
1. Gut Health
2. What is IMO?
2.1 Eukaryotes vs. Prokaryotes? Archaea vs. Bacteria?
2.2 Consequences of IMO
2.3 Diagnosis of IMO
2.4 Treatment of IMO
3. SIBO vs. IMO?
4. Conclusion
1. Gut Health
Gut health is gaining increasing attention in medical research and public awareness. Besides well-known conditions like irritable bowel syndrome or small intestinal bacterial overgrowth (SIBO), a specific type of overgrowth is becoming more important: Intestinal Methanogen Overgrowth (IMO). This is not a bacterial but an archaeal overgrowth of the gut, which is associated with excessive methane production.
2. What is IMO?
IMO stands for “Intestinal Methanogen Overgrowth,” which describes an increase of methane-producing microorganisms, specifically archaea, in the gut.
These microorganisms, especially Methanobrevibacter smithii, Methanomassiliicoccus, and Methanosphaera stadtmanae (1,2), produce methane from hydrogen, which is formed by other gut bacteria.
Archaea are a distinct domain of microorganisms that differ fundamentally from both bacteria and eukaryotes. Although they often appear similar to bacteria externally, they show clear differences in their cell membrane structure, metabolism, and genetic organization.
2.1 Eukaryotes vs. Prokaryotes? Archaea vs. Bacteria?
Prokaryotes and eukaryotes differ fundamentally in their cell structure. Eukaryotes (including animals, plants, and fungi) have a nucleus that encloses their DNA, as well as various organelles with specific functions. Prokaryotes, on the other hand, do not have a nucleus; their DNA is free within the cell, and they lack membrane-bound organelles. Prokaryotes include two groups: bacteria and archaea. Both are unicellular and appear similar externally but differ in important molecular features. Archaea have unique cell membranes, use different metabolic pathways, and show more similarities in gene regulation with eukaryotes than with bacteria.
2.2 Consequences of IMO
Affected individuals with intestinal methanogen overgrowth (IMO) often suffer from constipation. The cause is methane produced by methane-forming microorganisms, which can slow down gut motility and significantly increase intestinal transit time (2). This can lead to symptoms such as constipation, bloating, belching, and a feeling of fullness.
A slowed intestinal transit also impairs the natural cleansing function of the gut, allowing microorganisms like archaea to settle and multiply more easily—a self-reinforcing cycle.
2.3 Diagnosis of IMO
The most common method for diagnosing IMO is the breath test, which measures the concentration of hydrogen and methane in the exhaled air after ingestion of lactulose or glucose. A significant increase in methane (over 10 ppm at any time) indicates IMO. It is important that the results are interpreted carefully by experienced professionals, as the tests are not always clear.
Another important aspect to consider when evaluating a breath test is that archaea are not typical bacteria and can colonize both the small and large intestines.
Studies, however, show that the methane concentration in the breath correlates with the severity of constipation.
2.4 Treatment of IMO
Archaea are difficult to target specifically, which is why treatment of IMO should ideally be carried out under medical supervision. The therapy resembles many aspects of SIBO treatment and includes, among other things, special diets, the use of certain antibiotics, as well as the complementary administration of pro- and prebiotics.
3. SIBO vs. IMO?
IMO is often confused with SIBO because the symptoms can overlap (2). However, the main difference lies in the causative agent: while SIBO is caused by bacterial overgrowth, IMO involves archaea (2). Nevertheless, IMO is sometimes referred to as a “subtype of SIBO.”
4. Conclusion
Intestinal Methanogen Overgrowth is a frequently overlooked but significant cause of chronic digestive complaints, especially therapy-resistant constipation. A thorough diagnosis and individually tailored treatment are crucial to improve the quality of life for affected individuals. Anyone suffering from persistent digestive problems should consider IMO as a possible cause and seek evaluation by an experienced specialist. You can find doctors trained through our SIBO Academy here.
References
- Takakura W, Pimentel M. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome – An Update. Front Psychiatry. 2020 Jul 10;11:664. doi: 10.3389/fpsyt.2020.00664. PMID: 32754068; PMCID: PMC7366247.
- Mechlińska A, Frąckiewicz K, Gładyś-Cieszyńska K, Buczek D, Dziadziuszko R. Small intestinal bacterial overgrowth and intestinal methanogen overgrowth in gastrointestinal malignancies. Contemp Oncol (Pozn). 2025;29(1):11-21. doi: 10.5114/wo.2025.148643. Epub 2025 Mar 18. PMID: 40330452; PMCID: PMC12051882.
