What causes SIBO - Small Intestinal Bacterial Overgrowth?

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When small intestinal bacterial overgrowth occurs, large intestine bacteria invade the small intestine and cause discomfort.

Trillions of bacteria live in the human intestine and together they form the intestinal flora (microbiome).

In a healthy digestive tract, these bacteria are predominantly found in the large intestine, where they have the task of processing undigested food residue (food pulp).

In the case of a bacterial overgrowth in the small intestine (Small Intestinal Bacterial Overgrowth, or "SIBO"), these bacteria colonize more in the small intestine, which can lead to abdominal pain, flatulence and a feeling of fullness a few hours after eating.

The causes of SIBO can be food intolerances, but also inflammation or malfunction in the body.

Small intestine malabsorption: The trigger behind digestive problems

The small intestine filters carbohydrates, fats and proteins from the food pulp. It normally contains only small amounts of bacteria, which are mainly regulated by gastric acid, bile and intestinal peristalsis.

The colon, on the other hand, is home to many bacteria that help metabolize incoming undigested food waste.

In a healthy, functional digestive system a one-way valve called the ileocecal cap (or mucosal cap) serves as a barrier between the small and large intestines. The purpose of the cap is to prevent bacteria from the colon (large intestine) from entering the small intestine and spreading excessively.

If the intestinal motor function is disturbed or the function of the valve is impaired, the large intestine bacteria can penetrate into the small intestine. Here they encounter an oversupply of nutrients, which they ferment and then start producing gases such as carbon dioxide, hydrogen, and methane.

As a result of bacteria in the small intestine, a person might experience symptoms such as:

  • Abdominal pain/abdominal cramps

  • Changed stool consistency: diarrhea or constipation

  • Flatulence / feeling of fullness

  • Nausea

  • Expulsion (extreme urgency to use the bathroom or accidents)

  • Fatigue

The increased amount of bacteria in the small intestine produces acids that can damage the mucosa of the small intestine which can be an impediment to nutrient absorption as it causes malabsorption or poor digestion.

In some patients, this is manifested by weight loss, nutrient deficiencies, or impaired fat digestion with so-called fatty stools (light-colored, soft, greasy, and foul-smelling stools).

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SIBO: What is the cause and how is the diagnosis made?

SIBO Cause & Diagnose

Small intestinal bacterial colonization can have many causes. It can occur due to inflammation/inflammatory bowel disease (Crohn's disease), food intolerances, after bowel surgery, or diverticula (intestinal wall bulges) of the small intestine.

It can also be caused by decreased bowel activity (motility disorders) due to other diseases, such as diabetes.

Diagnosis of small intestinal malabsorption can be made using a hydrogen breath test, which is also used to diagnose lactose intolerance as well as fructose intolerance. It is relatively inexpensive and simple and can usually be performed on an outpatient basis.

A blood test also provides additional information as to whether iron or any other vitamin deficiencies are present, which can also indicate small intestinal malabsorption.

Imaging techniques (for example, MRI or ultrasound) can be used to rule out functional causes of small bowel malabsorption.

Small Intestinal Bacterial Overgrowth: What are the treatment options?

If a functional disorder is present as the cause of the small intestine malabsorption, treatment consists primarily of therapy for this cause.

Bacterial colonization of the small intestine can also be treated with antibiotics. Medications that improve the mobility of the small intestine can also alleviate the symptoms.

The most important treatment for small intestinal malabsorption, however, is a change in diet.

By avoiding sugary foods and short-chain carbohydrates, so-called FODMAPs, the bacteria in the small intestine will be deprived of their nutritional basis. Eventually, this leads to the dying off of the bacteria. The goal is then to prevent the bacteria from migrating back into the small intestine.

To prevent deficiency symptoms, a change in diet should always be accompanied by a trained dietician or nutritionist.

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