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Small Intestine Bacterial Overgrowth

(SIBO; Small Bowel Bacterial Overgrowth; SBBO)


Bacteria normally exists in the intestines. It plays an important role in digestion and overall health. Small intestine bacterial overgrowth (SIBO) is when there is too much bacteria in the small intestine.

The Small Intestines
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SIBO is often caused by a problem with the small intestine. Damage or defects to the intestine may slow the flow of food through the area. The slowed food may encourage the increased growth of bacteria. Problems of the intestine may be caused by:

  • Birth defect
  • Injury
  • Surgery
  • Digestive disorders

Risk Factors

Any condition that affects how food moves through the intestines may increase the risk of SIBO. Examples include:

Other risk factors include:

  • Intestinal surgery
  • An obstruction in the small intestine
  • Weakened immune system
  • Older age


SIBO may cause:


Your doctor will ask about your symptoms and medical history. A physical exam will be done.

Tests may include

  • Blood tests
  • Breath tests—to look for certain gases after fasting and eating specific sugars
  • Culture of intestinal fluid—a sample of fluid from the small bowel; tests will help to see what bacteria is present


The goal of treatment is to:

  • Reduce the levels of harmful bacteria in the small bowel
  • Treat any underlying conditions


Antibiotics are often used to treat SIBO. Usually treatment is temporary. Some may need to take antibiotics for a longer period.

Nutritional Support

Proper nutrients can help bring back the balance of bacteria. Steps that may help include:

  • Work with a dietitian
  • Follow a special diet, such as a carbohydrate-restricted diet
  • Take vitamins and/or supplements
  • Take probiotics

In some cases, tube feeding is needed with a special formula.


Surgery may be needed for severe SIBO. It may be needed to correct a problem in the small bowel.


If you have any of the conditions that are linked to SIBO, get proper treatment. This may reduce your chance of having a build-up of bacteria in the small bowel.


American Gastroenterological Association

National Institute of Diabetes and Digestive and Kidney Diseases


Canadian Association of Gastroenterology

Canadian Digestive Health Foundation


Bacterial overgrowth syndrome. Merck Manual Professional Version website. Available at: Updated May 2016. Accessed October 3, 2017.

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

Lactose and glucose hydrogen breath test. Cleveland Clinic website. Available at: Accessed October 3, 2017.

Lin H. Small intestinal bacterial overgrowth. JAMA. 2004;292(7):852-858.

Short bowel syndrome. EBSCO DynaMed Plus website. Available at: Updated May 6, 2014. Accessed October 3, 2017.

Vanderhoof J, Young R, Murray N, Kaufman SS. Treatment strategies for small bowel bacterial overgrowth in short bowel syndrome. J Pediatr Gastroenterol Nutr. 1998;27(2):155-160.

Last reviewed September 2018 by EBSCO Medical Review Board Daus Mahnke, MD  Last Updated: 2/6/2018