SIBO is classified based on the type of gas produced by the bacterial overgrowth: Hydrogen-dominant SIBO: Characterized by the production of hydrogen gas, often associated with bloating and diarrhea. Methane-dominant SIBO: Associated with methane gas production, leading to constipation and slower bowel movements. Hydrogen sulfide SIBO: A less commonly discussed type, associated with symptoms such as diarrhea and foul-smelling gas.