Small Intestinal Bacterial Overgrowth (SIBO) and Fructose Intolerance


calendar_today   APR 12, 2023
SIBO and Fructose Malabsorption

What is Small Intestine Bacterial Overgrowth (SIBO)?

Small Intestine Bacterial Overgrowth, or SIBO, refers to when the wrong type of bacteria inhabit the small intestine, as the name suggests. But what does that really mean?

In humans, the small intestine is divided into three sections and its length can vary between three and six meters, depending on muscle tension. This is where nutrients are broken down and absorbed. Compared to the large intestine, the small intestine has few bacteria, at least when healthy. Moreover, the type and number of bacteria in the small intestine are different from those in the large intestine.

How does SIBO occur?

Between the small and large intestines is the ileocecal valve, forming a clear boundary between the two. If this valve doesn't close properly or is "pushed open" by excessive gas, bacteria from the large intestine can move into the small intestine. 

Once there, they can outcompete the normal flora of the small intestine. Other causes can include decreased stomach acid production, physical changes in the digestive tract (e.g., from surgery), or aging. Often, a combination of these factors is involved.

Normally, there are 10^3 bacteria per milliliter of small intestine mucus. When there are 10^5 to 10^6, it is defined as SIBO.

What are the typical symptoms?

The migrated bacteria start fermenting sugars in the small intestine. This produces gas, which causes typical bloating. Smaller amounts of gas can be absorbed into the bloodstream and then breathed out through the lungs. But with SIBO, large amounts of gas are produced that can't be fully absorbed. Unlike the large intestine, this gas cannot be expelled as flatulence. The resulting expansion of the small intestine wall causes discomfort and pain.

Another common symptom is diarrhea, triggered by short-chain fatty acids that bacteria produce during carbohydrate digestion. Some people might experience fatty stools. Often, these symptoms are misdiagnosed as irritable bowel syndrome but can disappear once the SIBO is treated.

SIBO Symptoms

Are there any long-term effects?

If untreated, SIBO can lead to weight loss and a deficiency in fat-soluble vitamins like A, D, E, and K. Moreover, the wrongly situated bacteria consume Vitamin B12, which in the worst case can lead to severe deficiency resulting in anemia and neurological symptoms.

"... the wrongly situated bacteria consume Vitamin B12, which in the worst case can lead to severe deficiency resulting in anemia and neurological symptoms."

How is SIBO diagnosed?

When suspecting SIBO, a hydrogen breath test can be conducted, similar to testing for fructose malabsorption. However, for determining SIBO, glucose or synthetic sugar are used. This test measures the rise of hydrogen in breath after consuming a sugar solution. If the small intestine has a significant amount of unwanted bacteria, they will produce hydrogen shortly after consumption, which then becomes detectable in the breath.

What does treatment look like?

Treatment for SIBO can include antibiotics, especially Rifaximin, which is not absorbed by the body and works only in the intestines. Probiotics, which contain a selection of important bacterial strains, can positively influence gut flora. 

They can help promote the growth of essential lactic acid bacteria, which in turn assist in pushing out the unwanted bacteria. Especially after antibiotic treatment, taking a probiotic can help reestablish a healthy gut bacterial composition.

Dietary changes can also be effective. Temporarily avoiding carbohydrates can essentially "starve out" the unwanted bacteria in the small intestine.

What's the connection between SIBO and fructose malabsorption?

There seems to be a two-way relationship between fructose malabsorption and SIBO.

On one hand, fructose may support the survival of unwanted bacteria in the small intestine by providing them with easily digestible food, like "fast food". Increased gas from fructose malabsorption can also "push open" the ileocecal valve, promoting SIBO or exacerbating it.

On the other hand, antibiotic treatment for many SIBO patients often results in the simultaneous disappearance of fructose malabsorption symptoms. In some cases, fructose malabsorption might even be caused by SIBO. 

While these are still theoretical considerations without sufficient data, some scientific publications hint at a connection. It's wise to keep this in mind if diagnosed with fructose malabsorption and possibly discuss it with your doctor.

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