Small intestinal bacterial overgrowth (SIBO), defined as excessive bacteria in the small intestine, and, increasingly, the wrong type, remains a poorly understood disease. It was initially thought to occur in only a small number of patients. However, it is now apparent that this disorder is more prevalent than previously thought. Patients with SIBO vary in presentation, from being only mildly symptomatic to suffering from chronic diarrhea, weight loss, and malabsorpti

Methane-producing gut organisms such as M. smithii have been implicated in constipation-predominant IBS.


Moreover, there is an increasing amount of research data that suggest that some forms of Irritable Bowel Syndrome (IBS) are caused or made worse by SIBO. Hydrogen and methane breath tests are helpful in strengthening a presumptive diagnosis of SIBO. Unfortunately, many physicians do not offer these non-invasive tests for a variety of reasons.

Dr. Klaus Gottlieb has conducted some of the largest breath test studies currently available, helped establish cut-off levels for normal and abnormal methane levels in exhaled air, and was involved in clinical research that aimed to lower methane levels to help patients with constipation-predominant IBS (Irritable Bowel Syndrome). He understands SIBO and microbiome related issues and can help patients figure out how to address excessive bloating, diarrhea and abdominal pain either with prescription medications, supplements and probiotics, diet and other self-help measures.  

Gottlieb, Klaus, et al. “Selection of a cut-off for high-and low-methane producers using a spot-methane breath test: results from a large North American dataset of hydrogen, methane and carbon dioxide measurements in breath.” Gastroenterology Report (2017): gow048.

Gottlieb, Klaus T., et al. “Increased Pulmonary CO2 Excretion in Patients with Small Intestinal Bacterial Overgrowth (SIBO): Possible Implications for COPD.” Gastroenterology 152.5 (2017): S628.

Gottlieb, Klaus., et al. “Inhibition of methanogenic archaea by statins as a targeted management strategy for constipation and related disorders.” Alimentary pharmacology & therapeutics 43.2 (2016): 197-212.


More information about SIBO