Small Intestinal Bacterial Overgrowth (SIBO): Symptoms, Treatment

What Is Small Intestinal Bacterial Overgrowth (SIBO)?

Various bacteria are present in the human small intestine as part of normal intestinal flora, but when they overgrow, they may cause diarrhea. They may also break down bile acids, necessary for absorption of fats, thus reducing absorption of fats and fat-soluble vitamins A, D and E. In severe cases, bacteria may damage small intestinal wall thus impairing carbohydrate and protein absorption resulting in malnutrition. Anemia may develop, when bacteria break down vitamin B12.

Symptoms of SIBO

Symptoms of small intestinal bacterial overgrowth may include:

  • Early satiety (feeling full after only “few bites”), bloating and nausea, which forces many patients to avoid food, resulting in weight loss.
  • Sulphur burps
  • Some patients with SIBO crave sugar.
  • Chronic diarrhea – may appear weeks or even years after the causing event, like surgery (1).
  • Whitish, floating, foamy and sticky stool due to unabsorbed fats.
  • Muscle weakness and bone pains due to vitamin D deficiency.
  • Anemia with pale skin, weakness or tingling due to vitamin B12 deficiency.
  • Impaired night vision due to vitamin A deficiency.

Causes of SIBO

Why bacteria in the small intestine overgrow?

  • Ileocecal valve, separating the small and large intestine, may be insufficient due to inborn errorsbowel surgeryCrohn’s disease or other disorders, thus enabling bacteria from the large intestine, where they are present in large amount, to invade into the small intestine.
  • Slow intestinal motility, due to low gastric acid, acid-lowering drugs, like Prevacid, or pain-killers , like opiates, nerve damage in diabetes or overgrown fibrous tissue in systemic sclerosis, may allow bacteria to stay in the small intestine for a long time without being flushed away.
  • Liver disease, like cirrhosis.
  • Irritable bowel syndrome (IBS). Relation between SIBO and IBS is not entirely understood.

Diagnosis of SIBO

SIBO is diagnosed by a hydrogen breath test. A patient drinks a solution with sugar, which is broken down by small intestinal bacteria that yield hydrogen. Hydrogen enters the blood and appears in exhaled air, which is collected by a special machine. From an amount of hydrogen in the exhaled air, an amount of intestinal bacteria can be calculated.

Treatment of SIBO

SIBO is treated with antibiotics. Probiotic capsules given along with antibiotics help to maintain normal intestinal flora (1). Vitamins, minerals and other nutrients may need to be replaced; in severe malnutrition, intravenous feeding may be required


A person with poorly controlled diabetes, chronic gastrointestinal disease or recent surgery, experiencing excessive bloating, early satiety or sulphur burps, should consider small intestinal bacterial overgrowth as a possible cause.

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  1. Small intestinal bacterial overgrowth  (
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