What is SIBO? Diagnosis, Symptoms, and Treatment

There is increasing evidence that small intestinal bacterial overgrowth (SIBO) plays a role in the cause of irritable bowel syndrome (IBS). Most of the bacteria that live on or in humans are in the gastrointestinal (GI) tract, and each individual has a unique gut flora. Abdominal pain and bloating, burping, and passing gas bring patients to the doctor to sort out the cause. Can SIBO be the cause? Here’s what you need to know.  


What is SIBO?

Almost all of the bacteria in the gut are in the large intestine, the colon. Why? The slower the bowel, the easier it is for bacteria to set up shop, and the colon is the slowest. The small intestine usually has a low number of bacteria, so by definition, small intestinal bacterial overgrowth is having too many of your gut bacteria in the small intestine. As a result, SIBO is not an infection; instead, it’s a high number of bacteria in the small intestine where they don’t belong. 

How do bacteria in the gut cause abdominal symptoms? The gas produced by the bacteria may cause bloating, pain, and discomfort, among other symptoms. Bloating refers to a sensation of abdominal fullness, pressure, or a feeling of trapped gas. Therefore, the slower the gut moves, the easier it is for bacteria to stay in one place so think of SIBO as a motility disorder. 

What causes SIBO?

In short, we don’t have all the answers, but anything that slows the gut may cause SIBO. Irritable bowel syndrome (IBS) is currently the most common reason for SIBO and is now believed to have been triggered by food poisoning in the past. 

How to diagnose and treat SIBO?  

A breath test measures the presence of hydrogen, methane, and hydrogen sulfide in your breath after taking lactulose or glucose. More bacteria in your small intestine produce more hydrogen and methane, which will lead to a positive breath test for SIBO.  There are mail-in kits (your doc will look for those CLIA-certified) like Trio-Smart or some in-office options. 


What other tests should my doctor consider if I have bloating and diarrhea? Your doctor may start with a complete blood count test to evaluate for anemia, a “celiac panel” blood test (tTG, IgA), and stool studies.

If you have a + breath test, several regimens are available depending on the bacteria you overproduce (methane, hydrogen, or hydrogen sulfide). At this point, your doctor will discuss a regimen with you, which typically includes Xifaxan (Rifaximin).  

What is rifaximin (Brand name Xifaxan)?

Rifaximin is an antibiotic that works as an antibacterial but may also change the gut bacterial environment in other ways. Rifaximin is an effective treatment for irritable bowel syndrome (IBS-diarrhea predominant) and has been shown to improve symptoms in those with a positive breath test.


Diet changes

Dietary changes alone are not enough to treat SIBO. Stay tuned for more discoveries about which diet is the best for managing symptoms. A general recommendation is to eat the same amount as you usually do but as distinct meals with at least 4 hours between meals.  A “modified” low FODMAP diet helps, as less fermentable (the F in FODMAP) foods tend to produce fewer symptoms for patients with SIBO. Ask your doctor for more specific recommendations.

Dr. O.