Understanding IMO
What you need to know about “Methane SIBO” and Constipation
Every year millions of Americans find themselves facing uncomfortable and exhausting gastrointestinal issues like constipation, bloating, and abdominal discomfort. In fact, a survey published in the American Journal of Gastroenterology of over 70,000 adults revealed that 58% of respondents said they’d had two or more GI symptoms (including heartburn, constipation, bloating, diarrhea, or abdominal pain) just in the past week!
For some these are isolated incidents that resolve on their own. But for many, these symptoms never quite seem to go away–or get progressively worse over time–causing debilitating discomfort, pain, and changes in bowel habits that greatly affect their quality of life. So, if you’re here because you’re searching for answers to what’s going on inside your gut, you’re not alone... And you’ve come to the right place.
If you’ve been struggling with these types of issues for a while now, you may already have been told about IBS-C (constipation-predominant Irritable Bowel Syndrome) or perhaps even SIBO (Small Intestinal Bacterial Overgrowth). But, what if the root cause of your issues is something most people, and even many clinicians, aren’t talking about?
That something is IMO (Intestinal Methanogen Overgrowth). You might also have heard it called “Methane SIBO”, and that’s understandable. Google searches for “Methane SIBO” outnumber searches for “IMO” by more than 12 to 1, because this was the title given to this condition in the early days of research into the broader topic of intestinal microbial overgrowths, and the older name still lingers in gut health circles and older medical articles.
However, new discoveries are showing that that term isn’t quite accurate, since the methanogens (methane-producing organisms) that are the hallmark of IMO can cause an overgrowth in both the large and small intestines, and they are not bacteria. For the rest of the article we will only use the term IMO, which is the more precise, updated nomenclature.
IMO is an overabundance of methane-producing microorganisms in your intestines. While related conditions like SIBO are caused solely by bacteria, archaea are the main culprits that lead to IMO. Archaea are a group of single-celled organisms lacking a defined nucleus, and they are a distinct form of life, separate from bacteria, plants, animals and fungi. They often thrive in extreme environments like hot springs, salt lakes, or acidic ecosystems, and some types of archaea are known to live in your gut, where they play a role in digestion and metabolism.
Sure, it sounds alarming to think that these little organisms are living in your body, but it’s normal for some archaea to be present in your intestines. The problem comes when you are hosting too many of a certain kind.
So, what is IMO?
Many of the archaea that live in your gut are methanogens (The reason for the “M” in IMO). This means they are known to produce methane as a byproduct of their biological functions, often using the hydrogen gas in your gut as a substrate for their chemical reactions. Unfortunately, when methanogenic archaea are allowed to thrive in large numbers and there is enough hydrogen gas present in your intestines to fuel them, they can generate excessive amounts of methane gas.
And scientists have now found that methane can lead directly to constipation, bloating, and bowel irregularity. Let’s take a look at how that happens.
The Link Between Methane and Constipation
All that methane being produced in your gut doesn’t just hang around harmlessly. Decades of research has shown that methane actually changes the way your intestines move. Normally, the gut uses smooth, coordinated waves called peristalsis to push food and waste forward consistently. But when methane levels rise, the gut switches gears and the regular rhythm of your digestion is disturbed. Instead of steady forward motion, the intestines produce more of what are known as segmental contractions, squeezing in place without moving things along.
The link between methane and constipation is both observable and significant. In controlled laboratory studies, methane infusion slowed intestinal transit by nearly 60% compared with normal conditions, while also making contractions stronger and more frequent. That means food and stool linger longer in the digestive tract, giving the body extra time to absorb water. The result? Harder, drier stools that are difficult to move, more bloating, and that frustrating cycle of chronic constipation.
Put simply: when methanogenic organisms overgrow in your gut and have plenty of hydrogen to fuel them, they can pump out enough methane to disrupt your digestive rhythm. For many people this is the hidden reason why constipation doesn’t improve with fiber, probiotics, or dietary changes alone. It may also be the reason why a diagnosis of IBS or IBS-C hasn’t led you to the relief you are looking for.
If you have IMO and only treat your symptoms, but don’t address the underlying cause–the microorganisms producing all that methane–you are less likely to be able to manage or reduce your constipation, bloating, and discomfort.
How Do I Know if I’m At Risk? Symptoms of IMO
If you’ve had gastrointestinal issues for any length of time, you have probably experienced some frustration when trying to narrow down your search for answers. Since so many GI conditions share similar symptoms, and those symptoms can often be erratic and confusing, it can be an extreme challenge to attempt to get more information, let alone a specific diagnosis. And something like IMO–which is not as universally known as other conditions, like IBS or Ulcerative Colitis–can easily fly under the radar. Additionally, many people chalk up constipation or bloating to diet, stress, or “just how their body works”, when in fact methanogenic overgrowth could be the hidden driver.
So, what should you be looking for?
The signature symptom of IMO is constipation. Since the correlation between methane and slowed gut transit is so strong, constipation is by far the most consistent indicator of IMO and is present in the vast majority of cases. If you find yourself having infrequent bowel movements, hard or dry stools, or feeling like you can’t fully empty when having bowel movements, methane could be playing a role.
Other common symptoms include:
-
Bloating and gas that often worsen as the day goes on
-
Abdominal discomfort or cramping
-
Excessive straining or the sensation of incomplete evacuation
-
Sluggish digestion or feeling “backed up” even after a bowel movement
While IMO can affect anyone, certain factors make it more likely:
-
A history or diagnosis of IBS-C
-
Recurrent or chronic constipation that hasn’t responded well to fiber, probiotics or laxatives
-
Previous diagnosis of IMO or “Methane SIBO” on a breath test
-
Medical conditions or surgeries that have resulted in slower gut motility
-
Prior food poisoning
What’s Next? The Importance of 3-Gas Breath Testing
If you’ve been experiencing some of the symptoms listed above or you think you may be at greater risk for developing IMO, the obvious question is “What should I do next?” Fortunately, after decades of studying the gut microbiome and how microbial overgrowths adversely affect normal digestion, medical understanding of how to recognize, diagnose, and manage these types of conditions has advanced tremendously.
Scientists now know that gases like methane, hydrogen, and hydrogen sulfide–the three main indicators of microbial overgrowths like IMO, SIBO, and ISO–can be measured from capturing samples of your breath and comparing the results to known standard thresholds. And, even better, this can be done from the comfort of your home using the Trio-Smart 3-Gas Breath Test, the only scientifically validated at-home breath test that looks at all three of these gases, giving you a better picture of what may be going on inside your gut.
As we’ve discussed, for identifying IMO the most important of these gases is methane. Ongoing studies have shown that the connection between methane and constipation is extremely strong, with the amount of methane present even providing an accurate indicator of the severity of your constipation. Dr. Pimentel, Executive Director of the Medically Associated Science and Technology (MAST) Program at Cedars-Sinai, and the leading expert on the science of microbial overgrowth and breath testing, puts it this way:
“Methane is intimately associated with constipation… In fact, there’s now a large series of studies, various investigators around the world proclaiming the same results, and a meta-analysis. But essentially, if the methane is present on the breath test at greater than 3 parts per million at any part during the test, the association to constipation is over 90%. The other very interesting aspect of methane is that methane is proportional. So the higher the … methane, the greater the patient’s constipation severity is.”
So, if breath tests reveal that your methane levels are above 3 parts per million (which is the guideline set forth by the North American Consensus Group on hydrogen and methane-based breath testing) this is a very reliable indicator that you are experiencing significant constipation. And there’s a strong chance that constipation could be linked to a microbial overgrowth like IMO.
How Can I Manage My IMO?
As we’ve seen, our understanding of IMO, its causes, and its effects on our digestive system has grown so much that it is now possible to evaluate the likelihood of methanogenic overgrowth more easily than ever. The development of at-home, noninvasive testing has been a huge leap forward for patients trying to find answers to their recurring gut issues. But, ultimately, the most important goal for you and your care team is to help you treat and manage the issues that are affecting your health and quality of life.
Once you have your breath testing results in hand, you will want to share the findings with your healthcare provider(s) so they can evaluate the data and your specific case, and tailor a course treatment that will work best for you. Like most medical conditions, there is no “one size fits all” strategy that can be used for every case in a population, so it’s critical that you discuss your symptoms and results with your physician.
There is hope out there for people with IMO, and there are known options for treatment and management. The American College of Gastroenterology guidelines recommend use of antibiotics to reduce the methanogenic overgrowth. Evidence strongly suggests that a multi-antibiotic approach–specifically a combination of rifaximin and neomycin–achieves significantly better results than treatment from a single antibiotic.
In a study conducted by the GI Motility Program at Cedars-Sinai Medical Center in Los Angeles, California, and published in the Journal of Clinical Gastroenterology, researchers found that 87% of subjects taking a combination of rifaximin and neomycin eradicated the methane in their breath tests. While these results do not mean that these patients found instant or everlasting relief, it demonstrates that antibiotics can play a critical role in addressing your IMO and its symptoms.
Additionally, you may be asked to engage in some diet modification with the intent of reducing sources that feed the methane-producing microorganisms in your system. Limiting fermentable carbohydrates that indirectly support methanogen populations and reducing or avoiding foods that induce constipation, specifically insoluble fibers such as whole grains and nuts, are some steps that may also help curtail your symptoms and the underlying microbial overgrowth that is causing them.
For more information on Low-Fermentation Eating, diet modifications, and other management options for microbial overgrowths, you can check out our Treatment Options article here:
Final Thoughts
Intestinal Methanogenic Overgrowth (IMO) potentially affects millions of people each year, just in the United States alone. Unfortunately, it has often been overlooked and unrecognized, even in the healthcare community. As someone suffering from gut issues like constipation, bloating, abdominal discomfort, or changes in bowel habits, it’s critical that you find out as much as you can about what may be causing these disruptive problems.
We know that finding answers can be frustrating, but don’t give up! Get as much information and data as you can. The more you find out about what’s going on inside your gut, the more likely it is that you and your healthcare team can develop a sustainable plan to get you back on the road to a healthier, happier You.
Frequently Asked Questions
Can I have both IMO and IBS-C?
Yes, and they often overlap. Intestinal Methanogen Overgrowth (IMO) isn’t a separate disease, but rather a condition where methane-producing archaea disrupt gut motility. IBS-C (constipation-predominant irritable bowel syndrome) is a diagnosis based on symptoms like chronic constipation, bloating, and abdominal pain. Many people diagnosed with IBS-C are later found to have methane overgrowth driving those symptoms. In fact, studies show that almost 38% of people with IBS-C test positive for methane on breath testing, suggesting IMO is a common but underrecognized cause of IBS-C symptoms.
Can IMO go away on its own?
It’s possible, but unlikely. Once methanogenic archaea become established in the gut, they tend to persist unless specifically treated. IMO is often chronic and intractable without intervention, because archaea are hardy organisms that thrive when hydrogen is available. Treatment aimed at reducing methane levels, usually with targeted antibiotics, sometimes in combination with diet and herbal approaches, is often needed to bring real relief.
Can methanogenic overgrowth cause weight gain?
While the link between methanogenic overgrowth and weight gain has not been studied in enough detail to draw a definitive conclusion, there’s growing evidence that it may contribute. Some studies suggest that people who produce methane may extract more calories from the same food compared to non-methane producers. This is because of the cross-feeding relationship: bacteria break down carbohydrates into hydrogen, and methanogenic archaea consume that hydrogen, making fermentation more efficient. The result is increased energy (i.e. more calories) harvested from the diet.
Can IMO come back after I’ve been treated for it?
Yes, relapse is possible. Methanogenic archaea like Methanobrevibacter smithii are very resilient, and while treatment can reduce their numbers and lower methane production, it may not eliminate them completely. Just like bacterial SIBO, IMO can recur if the underlying factors that allowed it to develop in the first place (such as slowed gut motility or structural issues in the intestine) aren’t addressed. This is a reason why some patients benefit from periodic breath testing, so they can monitor whether their methane levels are becoming elevated.
Is it important to test for all three gases?
Yes, absolutely. If you only test for one or two gases, you risk missing the real driver of symptoms. For example, someone may test negative for hydrogen but actually have methane-dominant overgrowth causing constipation, because the archaea are using up the hydrogen, but producing methane instead. That’s why comprehensive testing (like the Trio-Smart 3-Gas Breath Test) is increasingly seen as the gold standard.
Is Intestinal Methanogen Overgrowth (IMO) recognized as an official diagnosis?
Yes. IMO has its own ICD-10 code: K63.829 (Other specified diseases of intestine). This classification helps doctors, researchers, and insurance providers recognize IMO as a distinct medical condition, separate from but related to SIBO and IBS-C. Using this diagnostic code underscores that IMO is a legitimate, clinically acknowledged disorder—not just a vague description of methane-related constipation.
References:
https://time.com/6157312/digestive-health-constipation-hemorrhoids/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3895606/
https://pubmed.ncbi.nlm.nih.gov/16293652/
https://chriskresser.com/sibo-update-an-interview-with-dr-mark-pimentel/
https://pmc.ncbi.nlm.nih.gov/articles/PMC5418558/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10132719/