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Small bowel bacterial overgrowth

Overgrowth - 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.

Causes

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).

Symptoms

The most common symptoms are:

  • Abdominal fullness
  • Abdominal pain and cramps
  • Bloating
  • Diarrhea (most often watery)
  • Gassiness

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

Treatment

The goal is to treat the cause of the bacterial overgrowth. Treatment may include:

  • Antibiotics
  • 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.

Possible Complications

Severe cases lead to malnutrition. Other possible complications include:

References

El-Omar E, McLean MH. Gastroenterology. In: Ralston SH, Penman ID, Strachan MWJ, Hobson RP, eds. Davidson's Principles and Practice of Medicine. 23rd ed. Philadelphia, PA: Elsevier; 2018:chap 21.

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.

Text only

  • Small intestine

    Small intestine - illustration

    The small intestine is the portion of the digestive system most responsible for absorption of nutrients from food into the bloodstream. The pyloric sphincter governs the passage of partly digested food from the stomach into the duodenum. This short first portion of the small intestine is followed by the jejunum and the ileum. The ileocecal valve of the ileum passes digested material into the large intestine.

    Small intestine

    illustration

    • Small intestine

      Small intestine - illustration

      The small intestine is the portion of the digestive system most responsible for absorption of nutrients from food into the bloodstream. The pyloric sphincter governs the passage of partly digested food from the stomach into the duodenum. This short first portion of the small intestine is followed by the jejunum and the ileum. The ileocecal valve of the ileum passes digested material into the large intestine.

      Small intestine

      illustration

    A Closer Look

     

    Tests for Small bowel bacterial overgrowth

     
     

    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.

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