Small Intestinal Bacterial Overgrowth, or SIBO, is the overgrowth of the bacteria that live in the small intestine.

Every part of the digestive tract, from the mouth to the rectum, has a certain population of healthy bacteria living in it. We take probiotics, for example, to increase bacteria in the large intestine. A significant amount of bacteria should live in the large intestine. 

The small intestine, on the other hand, only needs a relatively small population of bacteria for its purposes. The small intestine is responsible for digestion and the breakdown of food, absorption of nutrients, and excretion of toxins from the liver. In other words, even the mouth has more bacteria than the small intestine. So SIBO occurs when the number of bacteria (while not necessarily pathogenic or abnormal) living in the small intestine becomes excessive. SIBO is about the location of bacteria, rather than the type.


The main symptoms of SIBO include gas, belching, bloating (especially after eating), abdominal pain, diarrhea, or constipation. All of which are very similar to Irritable Bowel Syndrome (IBS). In fact, up to 80 percent of IBS may be due to SIBO.

The bacteria that overpopulate the small intestine in the case of SIBO consume the nutrients there. And that issue causes the bacteria to grow and ferment, which causes gas. This is why the main symptom of SIBO is bloating or distention, resulting in gas and belching.

SIBO can also cause fatigue, mood changes, brain fog, poor digestion of food, and/or increased reactions to food (which can be a bacterial problem rather than a food problem). These are typically due to the excessive bacterial metabolites, or excretions by bacteria, in the small intestine.

The Cause

The cause of SIBO is generally due to displaced bacteria. The displacement happens after things like food poisoning, traveler diarrhea, or stomach flu. Bacteria can also be displaced by slow bowel transit time (constipation), poor digestive enzyme production, or poor stomach acid production. Digestive enzymes and stomach acid usually prevent bacterial overgrowth, so these factors can affect this condition if they are producing too slowly.

The most important thing when experiencing symptoms of SIBO is to get a test. The SIBO test is a simple breath test, in which the patient first drinks lactulose, and then blows into tubes that measure the gasses (methane and hydrogen and sometimes hydrogen sulfide). The test then offers information on how much bacteria are living in the different parts of the intestines.

Treatment for SIBO aims to move the bacteria through the digestive tract with antibiotics or herbal antimicrobials, in addition to healthy probiotics.



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