Small intestinal bacterial overgrowth is an abnormal overgrowth of bacteria in the small intestine. SIBO can be the result of bacteria usually found in the large intestine overgrowing in the small intestine.
SIBO is not only an overgrowth of pathogenic bacteria that cause food poisoning, but also an overgrowth of probiotic bacteria from the colon. These bacteria ferment starches and fibers into gases that damage the intestinal lining and cause a host of symptoms.
The colon should have lots of bacteria, but the small intestine should not have lots of bacteria. Below is an example of the expected number of bacteria found in various sections of the small intestine.
The difference between the number of bacteria found in the colon is exponentially more than the number of bacteria found in the small intestine.
The small intestine is comprised of three sections. Here is an example of the expected number of bacteria found in various parts of the small intestine. CFU stands for colony-forming units.
Duodenum (right below the stomach) – 0 CFU/ml (zero bacteria)
Jejunum – 100 CFU/ml
Ileum – 100 – 10,000 CFU/ml
The colon is meant to have 100,000,000,000 CFU/ml
The colon should contain a lot of bacteria, although the small intestine is not meant to have large amounts of bacteria.
SIBO is an overgrowth of bacteria over 10,000 CFU/ml.
The duodenum should have zero bacteria due to the presence of bile acids, HCL, and pancreatic enzymes that destroy bacteria. The antibacterial control of the small intestine includes HCL, pancreatic enzymes, and bile acids.
Optimizing digestive function is always my first step involved in healing and preventing SIBO. I don’t use antimicrobials until I have optimized the digestive function of the three primary digestive organs.
The primary organs involved in maintaining the optimal terrain in the upper digestive system and small intestine are the gallbladder, pancreas, and stomach.
SIBO is estimated to cause 60-80 % of IBS cases. Small intestinal bacterial overgrowth should always be considered in individuals with IBS.
There are three different types of SIBO with polar opposite symptoms making SIBO symptoms even more confusing.
Types of SIBO
IBS-D (diarrhea dominant SIBO)
IBS-C (constipation dominant SIBO)
IBS-M (mixed diarrhea and constipation)
I know confusing, but knowing what bowel tendencies you experience can help to indicate what type of gases and bacteria are likely contributing to your SIBO Symptoms.
The bacteria that have overgrown in the small intestine produce gas as a result of fermentation upon starches and fibers. Depending on the presence of hydrogen-producing bacteria, methane-producing bacteria and hydrogen sulfide producing bacteria, various gases are produced such as:
- hydrogen gas
- methane gas
- hydrogen sulfide gas
This production of gas is normal if it was happening in the colon. It is not normal to have excess fermentation and gas production in the small intestine.
Bacteria that produce methane gas are associated with constipation, nausea, burping, and belching.
Hydrogen producing bacteria are associated with diarrhea, abdominal pain, and constipation.
Bacteria that produce hydrogen sulfide gas are more associated with diarrhea or constipation, foul gas that smells like rotten eggs, bladder pain, and joint pain.
A SIBO breath test can measure hydrogen and methane gas produced after consuming a glucose or lactulose substate. A breath test is used to diagnose SIBO.
In SIBO, the migrating motor complex is often impaired and allows for bacteria to stay in the small intestine. The migrating motor complex is a cleansing wave that passes through the small intestine to move food along.
If the migrating motor complex is not working properly, food stays in the small intestine longer allowing for excess bacterial fermentation and overgrowth to occur.
A host of digestive symptoms occur when bacteria overgrow in the small intestine.
Some of the most common SIBO symptoms include:
These are some of the gut symptoms of SIBO. Small intestinal bacterial overgrowth can have far-reaching implications on various systems of the body. SIBO is seen alongside many additional conditions, including headaches, anxiety, fatty liver, diabetes, rosacea, and more.