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Small Intestinal Bacterial Overgrowth (SIBO)

What is Small Intestinal Bacterial Overgrowth (SIBO)?

SIBO, also known as small bowel bacterial overgrowth (SBBO), refers to a condition in which abnormally large numbers of bacteria are present in the small intestine. This overgrowth of bacteria and other organisms competes with your body for the digestion of nutrients, such as vitamins (especially vitamin B-12). There is also malabsorption of sugars and carbohydrates, which are then passed to the colon where greater amounts of gas are produced, causing bloating, abdominal discomfort and loose stool. The lactulose or glucose breath tests are the standard tests for SIBO. (Learn more about SIBO from Melinda Dennis, MS, RD, LDN.)

The small intestine is the section of the gastrointestinal tract that connects the stomach with the colon (the large intestine). The main purpose of the small intestine is to digest and absorb food into the body.

Most people have between 300–500 different species of bacteria in their gastrointestinal tracts. Most of these bacteria are in the middle and the last part of the small intestine and also in the colon. The upper part of the small intestine and the stomach are generally too acidic and have too many muscular contractions for most bacteria to survive.

Symptoms of SIBO

  • Bloating
  • Gas
  • Abdominal pain
  • Feelings of fullness
  • Lack of appetite 
  • Malnutrition 
  • Weight loss
  • Diarrhea

What is the Connection between SIBO and Celiac Disease?

Studies have found a connection between SIBO and celiac disease, but more recent research has raised some questions about how strong that connection is.

In particular, SIBO seems to affect those with celiac disease whose symptoms continue despite the gluten-free diet. When it comes to treatment, the effectiveness of the antibiotic Rifaximin has had mixed results in scientific investigation. One 2011 study noted that patients with celiac disease may have more resistant SIBO or the symptoms associated with SIBO could be attributed to a variety of causes. 

A 2017 study noted that SIBO is difficult to diagnose properly, and people’s symptoms don’t always respond well to treatment. The study concluded that links between SIBO and celiac disease have been identified, mainly in people with ongoing symptoms of celiac disease. The exact mechanisms of this association are not well known, but it could be that alterations in mucosal defense and shifts in dietary composition can alter mucosal microbial diversity and populations. This could potentially give rise to SIBO in certain individuals.

The lack of accurate diagnostics for SIBO needs to be addressed before it will be possible to show causality or mere association between SIBO and celiac disease, the study says. Understanding of the mechanisms involved in the development of SIBO, perhaps using new technologies centered on culture-independent microbial identification, this could lead to better diagnosis and treatment for both conditions.

In earlier research, investigators theorized that disturbed motility of the intestine that can be associated with celiac disease might explain any association with SIBO. A 2007 study classified celiac disease as a motility disorder that can cause SIBO. The study included 15 symptomatic celiac disease patients on a gluten-free diet and found 66 percent had SIBO and all had a resolution of their symptoms after being treated for bacterial overgrowth. 

Here’s what Beth Israel Deaconess Medical Center says about SIBO and celiac disease, with the latest revision in the information made in 2012:

“SIBO is a common problem in celiac disease that appears to be caused by the intestines moving too slowly or irregularly. Decreased function of the immune system also appears to play a role. When these problems occur, they allow large numbers of “bad” bacteria to grow in the FIRST part of the small intestine where they normally do not grow.

Bad bacteria and other organisms also digest and use up vitamins, starches, protein and fat before the body can use them. Left untreated, SIBO can result in persistent damage to the villi, leading to vitamin deficiencies and elevations in celiac antibody levels. Diet changes, as well as antibiotics and probiotics, can be used alone or together to treat SIBO.”

Where Can I Learn More?


  • Leffler, D. Small Intestinal Bacterial Overgrowth. In Real Life with Celiac Disease: Troubleshooting and Thriving Gluten-Free. Dennis M, Leffler D, eds. AGA Press. Bethesda, MD, 2010.
  • Small Intestinal Bacterial Overgrowth. Accessed April 13, 2011.
  • Diet for IBS and SIBO. Specialists in Gastroenterology. Accessed April 13, 2011.
  • Scarlata K. Small intestinal bacterial overgrowth- what to do when unwelcome microbes invade. Today’s Dietitian, April 2011,13(4):46.

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