Small intestinal bacterial overgrowth (SIBO) may exist in up to 80% of individuals with irritable bowel syndrome (IBS). The small intestine, large intestine and all surfaces of your body are host to millions, even trillions of microbes. However, overgrowth of certain strains of microbes can be the cause of different disease conditions. SIBO is one such condition. The overabundant bacteria in the small intestine produce gas and can cause focal contractions of the intestinal tract, leading to IBS symptoms.