IBS, SIBO…IMO? Acronyms & your gut microbiome
What do these acronyms mean and what do they have to do with your digestion and gut microbiome?
IBS = Irritable bowel syndrome
You might be familiar with the first acronym, IBS, which stands for irritable bowel syndrome. It’s that diagnosis you get when other digestive causes have been ruled out and your healthcare provider is left shrugging their shoulders. The diagnostic criteria for IBS involves experiencing abdominal pain for at least one day per week for the last 3 months along with two out of the three associated symptoms: pain that’s related to defecation, change in stool frequency, and change in stool form.
For decades now, the question has still remained what causes IBS? I touched on various contributing factors to IBS in a previous article with stress often being an important factor that shouldn’t be overlooked (more on this to come). However a staggering amount of people who have IBS, up to 78% according to one meta analysis, test positive for something called SIBO or small intestinal bacterial overgrowth (Shah, 2010).
SIBO = small intestinal bacterial overgrowth
As the name describes, SIBO is defined as the presence of excessive bacteria in the small intestine leading to digestive symptoms. These bacteria end up fermenting nutrients that would normally be absorbed by the small bowel, and this fermentation may lead to gas production that contributes to symptoms of bloating and gas. Other symptoms of SIBO may include abdominal pain, distention, and diarrhea.
The gold standard for diagnosing SIBO is a small bowel aspirate and culture. This is an invasive procedure which involves a scope from the nose into the small intestine to obtain a fluid sample to be grown for bacteria. An alternative (and slightly more comfortable) method for diagnosing SIBO is an at-home breath test. This is based on the premise that human cells are incapable of producing the gasses hydrogen and methane. These gasses will be produced by bacteria in the digestive tract after fermentation of carbohydrates, then absorbed into the bloodstream, and expired through the lungs. It was previously thought that elevated hydrogen or methane gasses detected on this test indicated the presence of SIBO. However in recent years, we’ve been able to differentiate what hydrogen vs methane production tells us.
IMO = intestinal methanogen overgrowth
Which brings us to the third acronym, IMO. IMO stands for intestinal methanogen overgrowth. Note the absence of the terms “small” and “bacteria” in this name. That’s because methane production doesn’t occur from bacteria, it actually comes from a different type of organism called archaea. And these methane producing archaea (also known as methanogens) can be problematic anywhere in the digestive tract, not just the small intestine. While diarrhea is associated with hydrogen producing SIBO, it’s more common to see constipation with IMO. It’s been suggested that the level of methane found on a breath test is proportional to the severity of constipation experienced (Chatterjee, 2007).
What does it all mean?
Why do we care if you have SIBO vs IMO? Because treatment will be different based on the type of bacteria or methanogen overgrowth that’s contributing to your symptoms. We touched on the fact that this overgrowth results in the fermentation of foods in your digestive tract, specifically carbohydrates, which contributes to gas formation. There are particular foods, such as FODMAP foods that these bacteria really enjoy fermenting. Reducing these FODMAP foods may help reduce symptoms, but it’s not a sustainable treatment as it can result in a diet that’s too restrictive. It’s also not getting to the root of the problem as the overgrowth will still be present. Treatment involves eradicating or killing off the overgrowth using antibiotics, or anti-microbial herbs. In 2015, the U.S. Food and Drug Administration approved the antibiotic rifaximin for the treatment of diarrhea-based IBS with the understanding that one of the underlying factors of IBS is disruptions in the gut microbiome (Pimentel, 2020). As a naturopathic doctor, I also employ anti-microbial herbs when relevant such as in the case of IMO.
With a background in microbiology, I find the gut microbiome fascinating. Whether you found this article fascinating or confusing, I urge you to continue asking the age-old naturopathic question of “why”? Why do you have IBS? To understand if SIBO, IMO, or some other factors are contributing to your digestive concerns, please reach out instead of suffering through.
In good health,
Dr. Meghan Dougan,
Naturopathic Doctor
References:
Shah E., Basseri R., Chong K., et al. (2010). Abnormal breath testing in IBS: A meta-analysis. Digestive Diseases and Sciences, 55(9), 2441-2449. doi: 10.1007/s10620-010-1276-4
Chatterjee S., Park S., Low K., et al. (2007). The degree of breath methane production in IBS correlates with the severity of constipation. American Journal of Gastroenterology 102(4), 837-841. doi: 10.1111/j.1572-0241.2007.01072.x
Pimentel, M., Saad R., Long, M., Rao, S. (2020). ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. The American Journal of Gastroenterology 15(2), 165-178. doi: 10.14309/ajg.0000000000000501