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Small Intestinal Bacterial Overgrowth (SIBO)


Zubair Malik

, MD, Lewis Katz School of Medicine at Temple University

Reviewed/Revised Mar 2023

Small intestinal bacterial overgrowth 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 Overview of Malabsorption Malabsorption syndrome refers to a number of disorders in which nutrients from food are not absorbed properly in the small intestine. Certain disorders, infections, and surgical procedures can... read more ).

  • Some conditions and disorders slow or stop the movement of contents through the intestines.

  • People have abdominal discomfort, diarrhea, bloating, and excessive flatulence.

  • The diagnosis is based on symptoms, particularly in people who have had certain types of surgery or who have certain disorders, plus the results of a breath test or an intestinal fluid culture.

  • Antibiotics can eliminate the excess bacteria.

Causes of SIBO

Symptoms of SIBO

The most common symptom of small intestinal bacterial overgrowth is bloating.

Other symptoms are abdominal discomfort, diarrhea Diarrhea in Adults Diarrhea is an increase in the volume, wateriness, or frequency of bowel movements. (See also Diarrhea in Children.) The frequency of bowel movements alone is not the defining feature of diarrhea... read more , excess flatulence, weight loss, or symptoms of nutritional deficiencies. Some people have severe diarrhea or steatorrhea (light-colored, soft, bulky, greasy, and unusually foul-smelling stool).

Diagnosis of SIBO

  • A doctor's evaluation of symptoms

  • Breath tests

  • Intestinal fluid culture

  • Imaging tests

Doctors base the diagnosis of small intestinal bacterial overgrowth on typical symptoms, particularly in people who have had certain types of surgery or have certain disorders.

Doctors may take a fluid sample from a flexible tube inserted into the small intestine in a procedure called endoscopy Endoscopy Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). In addition to examinations, doctors can use endoscopy to do biopsies and give treatment. Endoscopes... read more . Doctors culture the fluid to determine the type and amount of bacteria present.

Or doctors may do a breath test. When bacteria in the intestines break down certain sugars, hydrogen and methane are produced. Doctors do a breath test to help them determine how much hydrogen or methane a person exhales through breathing. After drinking a liquid containing a certain sugar (glucose or lactulose) mixed with water, a person exhales into a collection bag at 1-hour intervals over a period of 4 hours. The bags are then analyzed. If the amount of hydrogen or methane in the breath rises significantly after consuming either of the liquids, the person has small intestinal bacterial overgrowth.

Sometimes people have abnormalities of their internal structures that make them susceptible to bacterial overgrowth. To identify these abnormalities, doctors take x-rays of the stomach and small intestines after a person drinks a liquid that shows up on x-rays (called an upper gastrointestinal [GI] series).

Treatment of SIBO

  • Antibiotics

  • Changes in diet

Most people get better with antibiotics given by mouth for 10 to 14 days.

Because the excess bacteria grow faster with carbohydrates, people should eat a diet higher in fat and lower in carbohydrates and fiber.

Doctors prescribe supplements to correct any nutritional deficiencies.

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