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Small intestinal bacterial overgrowth


Small intestinal bacterial overgrowth (SIBO) is a disorder whereby bacteria excessively grows in the small intestine; it is not a severe disorder and does not lead to organ damage. In its normal physiological state, the small intestine contains a small amount of bacteria, approximately 103-104 bacteria per milliliter. Bacteria ingested through eating are predominantly killed by gastric acid, which means that only minimal amounts of bacteria are detectable in the small intestine. The large intestine, on the contrary, houses a thick layer of bacteria consisting of approximately 1010-1012 bacteria per milliliter. These bacteria have numerous physiological functions, one of which is the further digestion of fermented food from the small intestine. Both the ileocecal valve, which separates the small intestine from the large intestine, and peristaltic waves, which ensure that digestive tract muscles contract smoothly, prevent the infiltration of large intestine bacterial flora into the small intestine. Additional mechanisms which prevent the spread of bacteria in the small intestine include immunoglobulins in the mucous membrane, pancreatic juice, and gall bladder bile.


Symptoms of SIBO can present 30-90 minutes after eating and they are triggered by bacteria caused malabsorption. On account of the build-up of gas, someone with SIBO usually feels bloated, experiences excessive flatulence, burps, and has bad breath. The pressure in the stomach resulting from gas can also cause nausea, heartburn, and spastic abdominal pain primarily located near the navel and right lower abdomen. Such symptoms can hinder the smooth contraction of digestive tract muscles (peristalsis) and lead to constipation or even diarrhea. Moreover, accelerated peristalsis means that certain fatty acids, vitamin B12 and iron are not well-absorbed and can subsequently lead to fatty stool, weight loss, and a deficiency state.

Chronic symptoms such as increased flatulence, colicky abdominal pain, and malabsorption can have a negative impact on a person’s quality of life.

Blind loop syndrome is a form of SIBO which ensues after abdominal surgery. The normal bacterial flora in the small intestine proliferates to an extent which significantly deranges the normal physiological processes of digestion and absorption.

If gas enters the large intestine, it collects and can cause pain on both sides of the ribs. In extreme cases, pressure on the diaphragm can lead to heart pain, shortness of breath, changes in skin pigment, and even exhaustion. In a nutshell, chronic digestion problems can reduce one’s overall well-being.

Medical examinations and diagnosis

SIBO can be diagnosed via a hydrogen breath test with lactose or glucose. After drinking a sugar solution, doctors measure hydrogen levels in the patient’s breath four times (during the lactose test, blood sugar levels are also measured). If a patient has SIBO, the presence of extra gas is detected through a noticeable increase in hydrogen levels. For the lactose test, doctors can also check whether the patient is lactose intolerant. In addition to the hydrogen breath test, patients can have secretion from the jejunum examined. A bacteria value exceeding 105/ml is a clear indication of SIBO.

It is necessary to differentially diagnose SIBO due to the general symptoms associated with it and the fact that SIBO can hide other digestive tract diseases. Diagnostic tests for this purpose include gastroscopy (for helicobacter and coeliac diseases), a histological examination for atrophic gastritis, colonoscopy (to exclude malignant or inflammatory stenosis, fistulas, and diverticulitis) and ultra sound examinations of the abdomen. For special cases, an MRI may be required. Lab tests are used to rule out diseases such as liver cirrhosis, diabetes, or AIDS, all of which can induce SIBO. Furthermore, hydrogen breath tests should be carried out to exclude the possibility of lactose and fructose intolerance while a stool examination can exclude pancreatic insufficiency and the presence of pathogenic bacteria or parasites. The prolonged use of anti-acid pills can be another promoter of SIBO.

Medical treatment

SIBO can be cured by taking antibiotics and other medication. Antibiotics like rifaximin, cotrimoxazol or metronidazol are widely recommended to treat SIBO. Supplementary probiotics like saccharomyces-cerevisiae can also be taken to combat the disorder. Should the onset of SIBO be caused by another disease, the patient would have to have this underlying disease treated as well.

Clinical course of the disease and prognosis

Overall, SIBO can cause chronic dysfunction of digestion and a general indisposition. It is easy to diagnose and can be healed with high efficacy.