Updated: Apr 26, 2019

SIBO is an abbreviation for small intestinal bacterial overgrowth. SIBO is defined as an excessive number or a change in the type of bacteria growing in the small intestine. In a healthy digestive tract, the majority of bacteria, yeast, and other microorganisms inhabit the large intestine (the colon), and only a very few take up residence in the small intestine. In patients with SIBO, we see colonic bacteria grow excessively in the small intestine. Sometimes this is caused by contents moving backward from the large to the small intestine, sometimes it is caused by a loss of the normal motility of the digestive tract (peristalsis), and sometimes it is caused by a lack of stomach acid (which allows bacteria to thrive).

Some studies report that more than 3 out of 4 patients with irritable bowel syndrome (IBS) also have SIBO. It is challenging to say whether this estimate is accurate because the diagnostic tests for SIBO are not always reliable. The gold standard for diagnosing SIBO requires a fluid sample from the upper part of the small intestine from an endoscopic tube. An easier test for SIBO is the breath test. For this test, the patient ingests sugar and measurements are taken from their exhaled breath. Hydrogen is detected in the breath when patients have SIBO with diarrhea symptoms, and methane is detected in the breath when patients have SIBO with constipation symptoms.

The symptoms of SIBO are very similar to the symptoms of IBS, making it difficult to distinguish these 2 conditions. There are a few clinical clues that suggest the presence of SIBO: patients with SIBO often feel temporarily better after taking antibiotics, they do not feel good taking prebiotics or probiotics, and they do not feel good eating fermented foods. Many times they are taking proton-pump inhibitors (such as Prilosec) to treat heartburn. The proton-pump inhibitors block the production of stomach acid, which can actually put a person at greater risk for bacterial overgrowth in the small intestine.

I often see patients who have been diagnosed with SIBO and treated with an antibiotic called rifaximin. Rifaximin is a very expensive medication that relieves the symptoms of SIBO about 64% of the time. Unfortunately, almost half of patients who respond well to antibiotics end up experiencing a relapse in their symptoms. This is probably because the antibiotics eliminate bacterial overgrowth but do not establish the proper gut terrain.

Successful long-term treatment of SIBO can include antibiotics but also requires additional gastrointestinal support. In addition to removing irritants and repairing the digestive lining, we work to rebalance the normal motility of the digestive tract. Gargling, for example, is a simple intervention that can help to retrain the muscular contractions of digestion. Properly spacing meals is also an important way to retrain normal gut motility. Patients with SIBO may benefit from additional digestive enzymes, supplemental hydrochloric acid, fewer or different probiotics, and other gastrointestinal support.


1 Bures J, Cyrany J, Kohoutova D, et al. Small intestinal bacterial overgrowth syndrome. World J Gastroenterol. 2010;16(24):2978-2990.

2 Pimentel M, Chow EJ, Lin HC. Eradication of small intestinal bacterial overgrowth reduces symptoms of irritable bowel syndrome. Am J Gastroenterol. 2000;95(12):3503-3506.

3 Lauritano EC, Gabrielli M, Scarpellini E, et al. Antibiotic therapy in small intestinal bacterial overgrowth: rifaximin versus metronidazole. Eur Rev Med Pharmacol Sci. 2009;13(2):111-116.

4 Lauritano EC, Gabrielli M, Scarpellini E, et al. Small intestinal bacterial overgrowth recurrence after antibiotic therapy. Am J Gastroenterol. 2008;103(8):2031-2035.

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About The Care Group: We promote optimal wellness by providing an individualized, functional medicine approach to address root causes rather than simply treating symptoms. We help patients with a wide range of issues including autoimmune/ inflammatory disease, digestive disorders, hormone imbalances, and mood disorders. To learn more about our practice, click here.

About the Author: Dr. Gerard Guillory, MD is Board Certified in Internal Medicine and has published two books on Irritable Bowel Syndrome (IBS). In 1985, he opened The Care Group, PC. Today, his clinic is a Primary Care facility that is a hybrid of functional and traditional medicine treating patients with digestive disorders, autoimmune disease, and other conditions. You can learn more about Dr. Guillory here.