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Small Intestinal Bacteria Overgrowth


What is Small Intestinal Bacterial Overgrowth (SIBO)?

There is normally a high concentration of bacteria in the colon, or large intestine, with a much smaller concentration in the small intestine. Peristaltic contractions (rhythmic contractions that propel food throughout the digestive tract) occur at regular intervals in a fasting state, about once every 90 minutes, and are partly responsible for keeping the bacteria down in the colon where they belong. However, in some people these rhythmic contractions do not occur as regularly as they should, allowing bacteria to migrate backwards from the large intestine up to the small intestine in abnormally high concentrations. This large amount of small intestinal bacteria can digest some foods before they can be absorbed by the small intestine, causing a variety of symptoms.

What are the Symptoms of SIBO?

SIBO can cause one or multiple of the following symptoms. Bloating and gas are very common SIBO symptoms.

  • Bloating
  • Gas
  • Abdominal pain and/or cramping
  • Diarrhea
  • Constipation
  • Fatigue
  • Nausea

How is SIBO Diagnosed?

The diagnosis of SIBO is typically made by a breath test called a “lactulose hydrogen breath test”, which is often available as a take-home kit. Above are video instructions explaining this test in detail. During this test, the patient will deliver a total of 10 breaths into 10 separate test tubes via an inflatable bag over the course of 3 hours. After the first sample baseline breath is collected, the patient will ingest a non-absorbed sugar called lactulose on an empty stomach. There are then 9 more sample breaths to be collected every 20 minutes at this point in the test. This sugar is not absorbed, but it does reach the bacteria in the small intestine, which metabolize it and produce one or more gases such as hydrogen and methane. These gases are excreted in the breath and can later be measured in a lab. The quantities of these gases and the amount they change over the course of the test is indicative of the number of bacteria in the small intestine (large amounts of gas indicates a “positive” breath test). A “positive” breath test indicates the patient has SIBO.

How is SIBO Treated?

The first line of SIBO treatment is often antibiotics. The type of antibiotic depends on the type(s) of bacteria that were over-produced during the breath test, the patient’s symptoms, and his/her clinical history. SIBO is a problem that can recur in some people, and so multiple rounds of antibiotics are sometimes necessary. Dietary modification, specifically, the low FODMAP, low fermentation, and SIBO diets are extremely helpful for some people in mitigating symptoms of SIBO. For people with recurrent SIBO, pro-motility medicine is another option.

Shahla Rah, MD, FACG
1525 Superior Ave, Suite 200
Newport Beach, CA 92663
Phone: 949-220-2886
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