Bacterial overgrowth syndrome is a disorder in which poor movement of intestinal contents allows certain normal intestinal bacteria to grow excessively, causing diarrhea and poor absorption of nutrients (malabsorption).

• Some conditions and disorders slow or stop the movement of contents through the intestines.
• Some people have no symptoms, whereas others have weight loss, nutritional deficiencies, and diarrhea.
• The diagnosis is based on symptoms that occur after people have had certain types of surgery.
• Antibiotics can eliminate the excess bacteria.

The normal steady movement of intestinal contents (peristalsis) is important to help maintain a proper balance of bacteria in the small intestine. Conditions in which intestinal contents slow or pool in one place allow excess bacteria to grow. Such conditions include certain types of surgery on the stomach, intestines, or both. Disorders such as diabetes, systemic sclerosis, and amyloidosis also can slow peristalsis, causing bacterial overgrowth.

The excess bacteria consume nutrients, including vitamin B₁₂ and carbohydrates, leading to lower calorie intake and vitamin B₁₂ deficiency. The bacteria also split bile salts, which are secreted by the liver to aid digestion. The loss of bile salts causes difficulty absorbing fats, leading to diarrhea and poor nutrition.

Some people have few symptoms or only weight loss. Others have severe nutritional deficiencies, diarrhea, or both.

Diagnosis and Treatment

Doctors base the diagnosis on typical symptoms that occur in people who have had certain types of surgery. Sometimes they take a fluid sample from the small intestine by means of a thin plastic tube passed through the nose. Some doctors instead perform breath tests, such as the ¹⁴C-xylose breath test. In this test, the person drinks a liquid containing a special, faintly radioactive marker (carbon-14) attached to a sugar (xylose). If the xylose is broken down by the excess bacteria, the carbon-14 can be detected in the person's breath.

Most people get better with antibiotics given by mouth for 10 to 14 days. Doctors prescribe supplements to correct any nutritional deficiencies.

Last full review/revision December 2007 by Atenodoro R. Ruiz, Jr., MD