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Small Intestine Bacterial Overgrowth

  • Cynthia M. Johnson, MA
Publication Type:


Small Intestine Bacterial Overgrowth

(SIBO; Small Bowel Bacterial Overgrowth; SBBO)


Bacteria live in the intestines and help with 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. Problems with the intestine may slow the flow of food. The slowed food may lead to more bacteria growing. Intestine problems may be caused by:

  • Problems that were there from birth
  • Injury
  • Surgery
  • Digestive disorders

Risk Factors

Any health issue that affects how food moves through the intestines may increase the risk of SIBO. Some problems are:

This problem is also more common in older adults. Other risk factors are:

  • Past intestinal surgery
  • An blockage in the small intestine
  • Having a weakened immune system


A person with SIBO may have:


The doctor will ask about symptoms and health history. A physical exam will be done.

Tests may include:

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


The goal of treatment is to lower the levels of harmful bacteria. Any underlying health problems will need to be treated.


SIBO cannot be prevented.


Antibiotics are often used to treat SIBO. Some may need to take antibiotics for a long period.

Nutritional Support

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

  • Working with a dietitian
  • Following a special diet, such one that limits carbohydrates
  • Taking vitamins or supplements
  • Taking probiotics

Some people may need tube feeding with a special formula.


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





  • Hydrogen breath test for lactose intolerance. Cleveland Clinic website. Available at: https://my.clevelandclinic.org/health/diagnostics/12360-hydrogen-breath-test-for-lactose-intolerance.
  • Short bowel syndrome. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/short-bowel-syndrome. Accessed August 20, 2021.
  • Small intestinal bacterial overgrowth (SIBO). Merck Manual Professional Version website. Available at: https://www.merckmanuals.com/professional/gastrointestinal-disorders/malabsorption-syndromes/small-intestinal-bacterial-overgrowth-sibo.
  • Small intestinal bacterial overgrowth (SIBO) syndrome. EBSCO DynaMed website. Available at: https://www.dynamed.com/small-intestinal-bacterial-overgrowth-sibo-syndrome.


  • James Cornell, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.