Small intestinal bacterial overgrowth (SIBO) occurs when there is an abnormal increase in the overall bacterial population in the small intestine — particularly types of bacteria not commonly found in that part of the digestive tract. This condition is sometimes called blind loop syndrome.
SIBO commonly results when a circumstance — such as surgery or disease — slows the passage of food and waste products in the digestive tract, creating a breeding ground for bacteria. The excess bacteria often cause diarrhea and may cause weight loss and malnutrition.
While SIBO is often a complication of stomach (abdominal) surgery, this condition can also result from structural problems and some diseases. Sometimes surgery is needed to correct the problem, but antibiotics are the most common treatment.
Signs and symptoms of small intestinal bacterial overgrowth (SIBO) often include:
Bloating, nausea and diarrhea are signs and symptoms of many intestinal problems. See your doctor for a full evaluation — especially if you've had abdominal surgery — if you have:
If you have severe abdominal pain, seek immediate medical care.
Small intestinal bacterial overgrowth (SIBO) can be caused by:
The small intestine is the longest section of your digestive tract, measuring about 20 feet (6.1 meters). The small intestine is where food mixes with digestive juices and nutrients are absorbed into your bloodstream.
Unlike your large intestine (colon), your small intestine normally has relatively few bacteria due to rapid flow of contents and the presence of bile. But in SIBO, stagnant food in the bypassed small intestine becomes an ideal breeding ground for bacteria. The bacteria may produce toxins as well as interfere with the absorption of nutrients. The breakdown products following bacterial digestion of food can also trigger diarrhea.
Factors that increase your risk of SIBO include:
Small intestinal bacterial overgrowth (SIBO) can cause escalating problems, including:
Poor absorption of fats, carbohydrates and proteins. Bile salts, which are normally needed to digest fats, are broken down by the excess bacteria in your small intestine, resulting in incomplete digestion of fats and diarrhea. Bacterial products may also harm the mucous lining (mucosa) of the small intestine, resulting in decreased absorption of carbohydrates and proteins.
Bacteria can compete for available food. And compounds produced through the bacterial break-down of stagnant food can also trigger diarrhea. Together, these effects of bacterial overgrowth result in diarrhea, malnutrition and weight loss.
Vitamin deficiency. As a result of incomplete absorption of fats, your body can't fully absorb the fat-soluble vitamins A, D, E and K. Bacteria in the small intestine synthesize as well as use vitamin B-12, which is essential for the normal functioning of your nervous system and the production of blood cells and DNA.
The overgrowth of bacteria can result in B-12 deficiency that can lead to weakness, fatigue, tingling, and numbness in your hands and feet and, in advanced cases, to mental confusion. Damage to your central nervous system resulting from B-12 deficiency may be irreversible.
In order to diagnose small intestinal bacterial overgrowth (SIBO), you may have tests to check for bacterial overgrowth in your small intestine, poor fat absorption, or other problems that may be causing or contributing to your symptoms. Common tests include:
In addition to these tests, your doctor may recommend blood testing to look for vitamin deficiency or a stool evaluation to test for fat malabsorption. In some cases, your doctor may recommend imaging tests, such as X-rays, computerized tomography (CT) scanning or magnetic resonance imaging (MRI) to look for structural abnormalities of the intestine.
Whenever possible, doctors treat small intestinal bacterial overgrowth (SIBO) by dealing with the underlying problem — for example, by surgically repairing a postoperative loop, stricture or fistula. But a loop can't always be reversed. In that case, treatment focuses on correcting nutritional deficiencies and eliminating bacterial overgrowth.
For most people, the initial way to treat bacterial overgrowth is with antibiotics. Doctors may start this treatment if your symptoms and medical history strongly suggest this is the cause, even when test results are inconclusive or without any testing at all. Testing may be performed if antibiotic treatment is not effective.
A short course of antibiotics often significantly reduces the number of abnormal bacteria. But bacteria can return when the antibiotic is discontinued, so treatment may need to be long term. Some people with a loop in their small intestine may go for long periods without needing antibiotics, while others may need them regularly.
Doctors may also switch among different antibiotics to help prevent bacterial resistance. Antibiotics wipe out most intestinal bacteria, both normal and abnormal. As a result, antibiotics can cause some of the very problems they're trying to cure, including diarrhea. Switching among different drugs can help avoid this problem.
Correcting nutritional deficiencies is a crucial part of treating SIBO, particularly in people with severe weight loss. Malnutrition can be treated, but the damage it causes can't always be reversed.
These treatments may improve vitamin deficiencies, reduce intestinal distress and help with weight gain:
Lactose-free diet. Damage to the small intestine may cause you to lose the ability to digest milk sugar (lactose). In that case, it's important to avoid most lactose-containing products, or use lactase preparations that help digest milk sugar.
Some affected people may tolerate yogurt because the bacteria used in the culturing process naturally break down lactose.
If you have signs and symptoms that are common to small intestinal bacterial overgrowth (SIBO), make an appointment with your doctor. After an initial evaluation, you may be referred to a doctor who specializes in treatment of digestive disorders (gastroenterologist).
Here's some information to help you get ready for your appointment, and what to expect from your doctor.
Don't hesitate to ask questions. Some basic questions to ask your doctor include:
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over points you want to spend more time on. You may be asked:
