SIBO Is Not a Single Condition

Small Intestinal Bacterial Overgrowth (SIBO) occurs when bacteria that should reside primarily in the large intestine colonise the small intestine in excessive numbers. But the type of gas these bacteria produce determines the symptom profile and, critically, the treatment approach. Getting this distinction right is the difference between effective treatment and months of frustration.

The Three Types of SIBO

Hydrogen-Dominant SIBO

In hydrogen-dominant SIBO, overgrown bacteria in the small intestine ferment carbohydrates and produce hydrogen gas as their primary metabolic byproduct. This is the most common form of SIBO and is diagnosed via a lactulose or glucose breath test showing elevated hydrogen levels.

Typical symptom profile:

  • Diarrhoea or loose stools (hydrogen accelerates gut transit time)
  • Bloating and abdominal distension, often worsening throughout the day
  • Urgency after eating, particularly high-carbohydrate or high-FODMAP meals
  • Nausea and early satiety
  • Nutrient malabsorption (particularly B12, iron, and fat-soluble vitamins)

Methane-Dominant SIBO (Now Called IMO)

Methane is produced not by bacteria but by archaea — specifically Methanobrevibacter smithii. Because these organisms can overgrow in both the small and large intestine, the condition has been reclassified as Intestinal Methanogen Overgrowth (IMO) rather than SIBO in the strictest sense.

Typical symptom profile:

  • Constipation (methane directly slows gut motility by up to 59%)
  • Bloating that is more constant and less meal-dependent
  • Weight gain or difficulty losing weight (methane promotes caloric extraction)
  • Belching and reflux symptoms
  • Less diarrhoea but more incomplete evacuation and straining
The hallmark distinction: hydrogen SIBO typically presents with diarrhoea; methane-dominant overgrowth typically presents with constipation. Mixed patterns occur when both gases are elevated.

Hydrogen Sulphide SIBO

The newest recognised type, hydrogen sulphide SIBO, involves bacteria that convert hydrogen into hydrogen sulphide gas. This form was difficult to diagnose until recently because standard breath tests did not measure hydrogen sulphide. The trio-smart breath test now includes this third gas.

Typical symptom profile:

  • Diarrhoea (often with urgency)
  • Sulphur-smelling gas (rotten egg odour)
  • Bladder irritation and urinary urgency
  • Visceral hypersensitivity (heightened pain perception in the gut)
  • Brain fog and fatigue (hydrogen sulphide is neurotoxic at elevated levels)

How to Get Tested

The lactulose breath test is the standard diagnostic tool. You consume a lactulose solution after an overnight fast and collect breath samples every 20 minutes for 3 hours. The test measures hydrogen and methane (and hydrogen sulphide with newer devices) over time.

Key interpretation points:

  • A rise of 20+ ppm in hydrogen within the first 90 minutes suggests small intestinal hydrogen overgrowth
  • Methane levels of 10+ ppm at any point indicate methanogen overgrowth
  • A flat hydrogen line (near zero) with symptoms may suggest hydrogen sulphide producers are consuming hydrogen

Why the Distinction Matters for Treatment

The treatment approach differs significantly by gas type:

Hydrogen SIBO

Responds well to Rifaximin (a gut-specific antibiotic) alone. Herbal alternatives include berberine, oregano oil, and neem. Diet during treatment: low-FODMAP to reduce substrate for bacterial fermentation.

Methane-Dominant (IMO)

Rifaximin alone is often insufficient because archaea are structurally different from bacteria. The standard approach is Rifaximin combined with Neomycin or Metronidazole. Herbal protocols typically combine allicin (garlic extract) with berberine-containing herbs, as allicin has specific anti-archaeal activity.

Hydrogen Sulphide H2S

Treatment is less standardised but typically involves Bismuth subsalicylate (which binds hydrogen sulphide) alongside Rifaximin. Dietary modification focuses on reducing sulphur-rich foods (eggs, cruciferous vegetables, garlic, onion) during the treatment phase.

The Underlying Cause Matters Most

Killing the overgrown organisms is only half the solution. Without addressing the root cause of the overgrowth, SIBO recurs in up to 45% of cases within a year. Common root causes include:

  • Impaired migrating motor complex (from food poisoning, adhesions, or medications)
  • Low stomach acid (from PPI use, ageing, or H. pylori infection)
  • Structural issues (ileocecal valve dysfunction, surgical adhesions)
  • Chronic stress (suppresses MMC activity through sympathetic dominance)

GutIQ's assessment helps identify symptom patterns consistent with specific SIBO types and underlying contributing factors, providing a foundation for targeted testing and treatment decisions.