Small bowel bacterial overgrowthOvergrowth - intestinal bacteria; Bacterial overgrowth - intestine; Small intestinal bacterial overgrowth; SIBO
Small bowel bacterial overgrowth is a condition in which very large numbers of bacteria grow in the small intestine.
Most of the time, unlike the large intestine, the small intestine does not have a large number of bacteria. Excess bacteria in the small intestine may use up the nutrients needed by the body. As a result, a person may become malnourished.
The breakdown of nutrients by the excess bacteria can also damage the lining of the small intestine. This can make it even harder for the body to absorb nutrients.
Conditions that can lead to overgrowth of bacteria in the small intestine include:
- Complications of diseases or surgery that create pouches or blockages in the small intestine. Crohn disease is one of these conditions.
- Diseases that lead to movement problems in the small bowel, such as diabetes and scleroderma.
- Immunodeficiency, such as AIDS or immunoglobulin deficiency.
- Short bowel syndrome caused by surgical removal of the small intestine.
- Small bowel diverticulosis, in which small, and at times large sacs occur in the inner lining of the intestine. These sacs allow too many bacteria to grow. These sacs are much more common in the large bowel.
- Surgical procedures that create a loop of small intestine where excess bacteria can grow. An example is a Billroth II type of stomach removal (gastrectomy).
- Some cases of irritable bowel syndrome (IBS).
The most common symptoms are:
- Abdominal fullness
- Abdominal pain and cramps
- Diarrhea (most often watery)
Other symptoms may include:
- Fatty stool
- Weight loss
Exams and Tests
Your health care provider will perform a physical exam and ask about your medical history. Tests may include:
- Blood chemistry tests (such as albumin level)
- Complete blood count (CBC)
- Fecal fat test
- Small intestine endoscopy
- Vitamin levels in the blood
- Small intestine biopsy or culture
- Special breath tests
The goal is to treat the cause of the bacterial overgrowth. Treatment may include:
- Medicines that speed intestinal movement
- Intravenous (IV) fluids
- Nutrition given through a vein (total parenteral nutrition – TPN) in a malnourished person
A lactose-free diet can be helpful.
Severe cases lead to malnutrition. Other possible complications include:
- Excess bleeding or other problems due to vitamin deficiency
- Liver disease
- Osteomalacia or osteoporosis
- Inflammation of the intestine
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Lacy BE, DiBaise JK. Small intestinal bacterial overgrowth. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 105.
Manolakis CS, Rutland TJ, Di Palma JA. Small intestinal bacterial overgrowth. In: McNally PR, ed. GI/Liver Secrets Plus. 5th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 44.
Sundaram M, Kim J. Short bowel syndrome. In: Yeo CJ, ed. Shackelford's Surgery of the Alimentary Tract. 8th ed. Philadelphia, PA: Elsevier; 2019:chap 79.
Review Date: 5/27/2020
Reviewed By: Jenifer K. Lehrer, MD, Department of Gastroenterology, Aria - Jefferson Health Torresdale, Jefferson Digestive Diseases Network, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.