Small intestinal bacterial overgrowth: what it is and what it is not

To critically review recent literature on small intestinal bacterial overgrowth (SIBO).

When originally described, SIBO was added to the list of causes of the malabsorption syndrome and the pathophysiology of its consequences for the digestion and absorption of various nutrients was gradually revealed. More recently, SIBO was incriminated as a cause of diarrhea, especially in the elderly. However, the suggestion that SIBO may be a causative factor in irritable bowel syndrome and of its constituent symptoms has sparked debate and controversy on the very definition of SIBO. This debate revolves around the tests employed and the diagnostic cut-off values (for bacterial numbers) used to diagnose SIBO in clinical practice.

A fundamental problem with SIBO, and one that allows controversy to simmer, is the lack of a universally accepted and applied gold standard for the diagnosis of SIBO. Hopefully, the application of molecular microbiological methods to the characterization of the small intestinal microbiome will tell us, once and for all, what is normal and when 'abnormality' is truly responsible for symptoms and disease. Meanwhile, therapy remains, for the most part, empirical and is based on the correction, wherever possible, of any underlying cause, attention to nutritional deficiencies, and the use of antibiotics.