The present invention relates to the treatment of a wide array of diseases and physiologic conditions based on modulating the level of hydrogen sulfide (H2S) in the body by at least partially eradicating small intestinal bacterial overgrowth (SIBO) in the gut. An H2S or lactulose breath test and/or detection of H2S or thiosulfate in the blood or urine may be used as a diagnostic and/or prognostic for assessing a systemic H2S load that exceeds a mammal's natural detoxification capacity. These tests may similarly be used to monitor the effectiveness of a therapeutic intervention for SIBO and/or the diseases or physiologic conditions whose pathology is linked thereto. Because SIBO is related to hyperhomocysteinemia, diseases and physiologic conditions that relate to hyperhomocysteinemia may further be monitored and treated in connection with the methods of the present invention.
