Small Intestinal Bacterial Overgrowth (SIBO) is a condition where excessive numbers of bacteria colonize the small intestine, leading to symptoms like bloating, abdominal pain, and altered bowel habits. While SIBO is often categorized by the production of hydrogen or methane gas, a distinct subtype is characterized by the production of hydrogen sulfide (H2S) gas. This H2S SIBO is fueled by sulfate-reducing bacteria and is strongly associated with diarrhea and the characteristic foul, “rotten egg” smelling gas. Treating this condition requires a tailored approach that addresses both the bacterial overgrowth and the high sulfur load that feeds it.
Diagnosing Hydrogen Sulfide SIBO
Identifying H2S SIBO historically proved difficult because standard breath tests only measured hydrogen and methane gases. Patients with this subtype often presented with classic SIBO symptoms but had a “flatline” result on a two-gas test. This flatline occurred because the hydrogen produced by other bacteria was immediately consumed by sulfate-reducing bacteria to create hydrogen sulfide.
Diagnosis is now significantly more accurate with specialized three-gas breath tests that directly measure hydrogen sulfide alongside hydrogen and methane. A positive diagnosis is typically made when H2S levels exceed a threshold of 3 parts per million (ppm) at any point during the test. This direct measurement allows practitioners to confirm the presence of overgrowth and better correlate gas levels with the intensity of symptoms like diarrhea.
Dietary Adjustments to Reduce Sulfur Load
Dietary modification is a primary strategy for managing H2S SIBO by temporarily limiting the fuel source for the sulfate-reducing bacteria. The goal of a low-sulfur diet is a strategic, short-term reduction to lessen the burden on the gut during the active treatment phase, not permanent elimination. Sulfur is found in amino acids present in most animal proteins and many plant sources.
High-sulfur foods need to be temporarily reduced. These include cruciferous vegetables like broccoli and cauliflower, and allium vegetables such as garlic and onions. Other sources contributing to the sulfur load are eggs, red meat, and dairy products. Certain supplements should also be avoided, particularly those containing sulfur-rich compounds like N-acetylcysteine (NAC) and methylsulfonylmethane (MSM). Because sulfur is an essential nutrient, this restrictive diet should be implemented with professional guidance to ensure nutritional sufficiency.
Targeted Antimicrobial and Neutralizing Protocols
The active “kill phase” of H2S SIBO treatment often involves a combination approach to reduce the overgrowth and neutralize the gas itself. Bismuth compounds, such as bismuth subsalicylate, play a dual role by acting as a mild antimicrobial and by directly binding to the hydrogen sulfide gas. This binding action provides rapid symptomatic relief by reducing the irritating effects of the gas on the intestinal lining.
Antibiotics are a standard part of the protocol, with Rifaximin frequently recommended to reduce overall bacterial overgrowth in the small intestine. Rifaximin is a broad-spectrum antibiotic that is minimally absorbed into the bloodstream, making it effective within the gut lumen. Herbal antimicrobials, such as emulsified oregano oil, are sometimes used as an alternative or in combination with pharmaceutical options to target the sulfate-reducing bacteria. Adjunct supplements, such as Molybdenum, can also support the body’s detoxification processes by assisting in the breakdown and clearance of sulfur compounds.
Promoting Gut Motility to Prevent Recurrence
Once the initial overgrowth is addressed, the focus shifts to preventing SIBO recurrence, which is often caused by impaired gut motility. The Migrating Motor Complex (MMC) is the small intestine’s “housekeeping wave,” a pattern of muscle contractions that sweeps undigested food and bacteria down into the large intestine during fasting. If the MMC is impaired, bacteria can linger and multiply, leading to relapse.
Prokinetics are agents used post-treatment to stimulate the MMC and maintain this cleansing action. These agents are distinct from laxatives and should be used for at least three months, and often long-term in chronic cases. Prescription options include medications like prucalopride, while natural prokinetics often contain ingredients like ginger extract. Supporting the MMC through prokinetics and by spacing meals at least four to five hours apart ensures the small intestine has time to clean itself and reduces the risk of the hydrogen sulfide-producing bacteria returning.