2d • General discussion
SIBO - Hydrogen Sulfide variant
Hydrogen sulfide small intestinal bacterial overgrowth — increasingly reclassified by leading gastroenterologists as Intestinal Sulfide Overproduction (ISO) — represents one of the most clinically challenging and underdiagnosed subtypes of gut dysbiosis. Unlike hydrogen-dominant SIBO (associated primarily with diarrhea) or methane-dominant SIBO/IMO (associated with constipation), ISO results from the unchecked proliferation of sulfate-reducing bacteria (SRBs) in the small intestine, producing hydrogen sulfide (H₂S) gas in pathological quantities.
For decades, standard three-gas breath testing only measured hydrogen and methane, leaving ISO systematically invisible. The advent of the TrioSmart™ breath test (Gemelli Labs) — the first commercially available test to measure all three SIBO gases simultaneously — has finally given clinicians a diagnostic window into this condition. Even so, many patients with textbook ISO symptoms go years without a diagnosis, and formal treatment guidelines remain absent.
This article synthesizes the current evidence base — including data presented at Digestive Disease Week (DDW) 2025 — to provide clinicians and informed patients with a practical, evidence-stratified approach to treating ISO/H₂S SIBO.
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SIBO - Hydrogen Sulfide variant
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