Intestinal methanogen overgrowth (IMO): Symptoms, testing, and treatment

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Section

Overview
Symptoms
Causes
Diagnosis
Treatment
Questions to ask

Symptoms

Treatment

What is intestinal methanogen overgrowth?

Intestinal methanogen overgrowth is often called IMO. It happens when too many methane-making microbes live in your digestive tract.

These microbes, called methanogens, are different from bacteria. They belong to a group of organisms called archaea. The most common one in the human gut is called Methanovrevibacter smithii. When bacteria break down food in the gut, they produce hydrogen gas. Methanogens use this hydrogen to produce methane gas.

Too much methane can slow how quickly food and stool move through your intestines. This may lead to digestive symptoms, especially bloating and constipation.

Unlike small intestinal bacterial overgrowth (SIBO), which mainly involves the small intestine, methanogens can overgrow in both the small intestine and large intestine (colon). This is why the name uses the broader term “intestinal” rather than “small intestinal.”

IMO is related to, but different from, SIBO. Some people may have both conditions. Roughly 1 out of every 3 people with SIBO also have IMO.

IMO vs. SIBO: What's the difference?

IMO	SIBO
What grows?	Methanogens, which are methane-making microbes	Bacteria in the small intestine.
Often linked with	Constipation, bloating, and alternating bowel habits	Diarrhea and bloating
Test	Breath testing	Breath testing and/or small bowel aspiration with a special catheter
Treatment	Care aimed at methane-making microbes and symptoms	Care aimed at extra bacteria and symptoms

Symptoms alone cannot show whether you have IMO, SIBO or both. A gastroenterologist can decide whether testing may help. 

What are the symptoms of IMO?

Constipation is one of the most common symptoms of IMO. Other symptoms may include:

Bloating or abdominal distention after eating.
Abdominal pain or discomfort.
Gas (flatulence).
Nausea.
Changes in how often you have a bowel movement.

These symptoms can have many causes. Having them does not always mean you have IMO. Symptoms alone cannot tell whether you have IMO, SIBO, or another digestive condition.

How does methane affect digestion?

Methane gas can slow the movement of food through your small intestine and colon. When food moves too slowly, stools can become harder and more difficult to pass. This may be why methane levels are linked to constipation, changes in bowel habits, and bloating.

Studies have shown that higher methane levels are consistently associated with slower gut transit, and treatments that lower methane often improve constipation. But it is not clear if the methane levels are high because of slow gut transit or slow gut transit leads to high methane levels.

What causes IMO?

Experts are still learning why some people have IMO. It may be linked to:

Changes in the mix of microbes in the gut.
Digestive disorders like irritable bowel syndrome (IBS), especially IBS with constipation (IBS-C), and chronic constipation.
Health problems that affect gut motility (how food moves through the digestive tract).
Prior abdominal or intestinal surgery, and inflammatory bowel disease.

How is IMO diagnosed?

Your healthcare provider may order a breath test. The test measures gases, including methane, in your breath. A methane level of 10 parts per million (ppm) or higher at any point during the test is used to diagnose IMO.

During the test:

You drink a special sugar drink, usually glucose or lactulose.
You breathe into a collection bag or tube at regular intervals.
The lab checks the gas in your breath.

Your healthcare team will tell you how to get ready. Follow all directions closely because they may affect the test result. Preparation usually involves:

Avoiding antibiotics for about 4 weeks.
Stopping laxatives and motility medicines for at least 1 week.
Eating a limited diet the day before the test.
Fasting for 8 to 12 hours before the test.

How is IMO treated?

IMO treatment depends on your symptoms, medical history, and test results.

Antiobiotics

Your gastroenterologist may prescribe antibiotics to lower the number of methane-making microbes in your gut. Take medicine only as directed.

Elemental diet

An elemental diet is a nutritionally complete liquid formula that is absorbed early in the digestive tract, can help reduce methane-producing microbes, and can be used as an alternative to antibiotics. It is usually taken as the only source of nutrition for about 2 weeks and should only be done under the guidance of your health care team. The main drawbacks are its taste, cost, and the difficulty of eating or drinking nothing else.

Diet changes

Some patients may benefit from changing what they eat. Approaches that reduce fermentable carbohydrates, such as a low-FODMAP diet, may help lessen gas and bloating, though they are not a cure. The evidence for diet in IMO is limited and mostly borrowed from research in IBS. Talk with a registered dietitian or gastroenterologist to find foods that may help you-

Managing constipation

Treatment may also include:

Drinking enough fluids.
Increasing physical activity.
Using a constipation medicine, if your healthcare provider recommends it.
Treating other health conditions that may be slowing your gut.

Can IMO come back?

Symptoms can come back after treatment. Tell your gastroenterologist if this happens. You may need more testing or a change in your treatment plan.

Questions to ask your healthcare team

Could IMO be causing my symptoms?
Should I have a breath test?
Do I have IMO, SIBO, or both?
What treatment is right for me?
Are there diet changes that may help?
What should I do if my symptoms come back?

When should I seek medical care?

Contact your healthcare team if you have:

Constipation that is not getting better.
Bloating that happens often.
Changes in bowel habits.
IBS symptoms that are not getting better.

Seek prompt medical attention for warning signs such as unexplained weight loss, blood in your stool, ongoing vomiting, or severe abdominal pain.

These symptoms can be caused by many different digestive conditions. A gastroenterologist can help determine whether testing for IMO may be appropriate.