Small Intestine Bacterial Overgrowth

(SIBO; Small Bowel Bacterial Overgrowth; SBBO)

by Cynthia M. Johnson, MA

Definition

Bacteria normally exists in the intestines. It plays a role in digestion and overall health. Small intestine bacterial overgrowth (SIBO) is when there is too much bacteria in the small intestine.

The Small Intestines

Causes

SIBO is often caused by a problem with the small intestine. Damage or defects to the intestine may slow the flow of food. The slowed food may encourage the increased growth of bacteria. Problems of the intestine may be caused by:

Birth defect
Injury
Surgery
Digestive disorders

Risk Factors

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

Crohn disease
Irritable bowel syndrome (IBS)
Short bowel syndrome
Diverticulitis
Intestinal stricture (narrowing in the small intestine)
Digestive disorders, such as celiac disease or lactose intolerance
A pancreas that is not making enough of the enzymes needed to break down food
Blind loop syndrome (when part of the intestine is bypassed)
Intestinal infections, such as food poisoning or traveler’s diarrhea
Cirrhosis
Diabetes
Chronic pancreatitis
End-stage kidney or liver disease

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

Prior intestinal surgery
An obstruction in the small intestine
Having a weakened immune system

Symptoms

Problems may be:

Belly pain
Bloating and gas
A feeling of fullness
Constipation or diarrhea
Weight loss

Diagnosis

The doctor will ask about your 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 specific sugars
Culture of intestinal fluid—a sample of fluid from the small bowel will be taken to see what bacteria is present

Treatment

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

Medications

Antibiotics are often used to treat SIBO. Usually treatment is temporary. Some may need to take antibiotics for a longer 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 as a carbohydrate-restricted diet
Taking vitamins and/or supplements
Taking probiotics

Some people may need tube feeding with a special formula.

Surgery

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

Prevention

There are no known guidelines to prevent this health problem.

RESOURCES:

American Gastroenterological Association
http://www.gastro.org

National Institute of Diabetes and Digestive and Kidney Diseases
https://www.niddk.nih.gov

CANADIAN RESOURCES:

Canadian Association of Gastroenterology
http://www.caghttps://www.cag-acg.org-acg.org

Canadian Digestive Health Foundation
http://www.cdhf.ca

References:

Hydrogen breath test for lactose intolerance. Cleveland Clinic website. Available at: https://my.clevelandclinic.org/health/diagnostics/12360-hydrogen-breath-test-for-lactose-intolerance. Accessed August 20, 2021.

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. Accessed August 20, 2021.

Last reviewed July 2021 by EBSCO Medical Review Board James Cornell, MD
Last Updated: 8/20/2021