SIBO Testing and Treatment Guide: Everything You Need to Know About Small Intestinal Bacterial Overgrowth

May 24, 2026

SIBO Testing and Treatment Guide: Everything You Need to Know About Small Intestinal Bacterial Overgrowth

By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist and founder of Casa de Sante

Key Takeaways

SIBO (small intestinal bacterial overgrowth) is present in up to 78% of IBS patients depending on the study — it may be the underlying cause of IBS in many cases
The hydrogen/methane breath test is the standard non-invasive diagnostic method. It is imperfect but the best available option.
There are three types: hydrogen-dominant SIBO (causes diarrhea), methane-dominant (now called IMO — causes constipation), and hydrogen sulfide SIBO (causes diarrhea + sulfur-smelling gas)
Treatment involves antimicrobials (rifaximin, herbal alternatives) + prokinetics (to prevent relapse) + diet modification + addressing the root cause
SIBO recurrence rate is 44% within 9 months without addressing the underlying cause. Root cause identification is critical.

Understanding SIBO

What It Is

The small intestine should have relatively few bacteria (<10^3 colony-forming units per mL). In SIBO, bacteria from the colon migrate into the small intestine, reaching levels of >10^5 CFU/mL. These bacteria ferment food prematurely, producing gas, bloating, pain, diarrhea or constipation, and malabsorption.

Root Causes

Impaired MMC (migrating motor complex): The #1 cause. Food poisoning can damage the MMC through autoimmune nerve damage (anti-vinculin and anti-CdtB antibodies). This is the post-infectious IBS pathway.
Low stomach acid: PPI use, aging, H. pylori infection. Acid kills bacteria before they reach the small intestine.
Structural issues: Abdominal adhesions (from surgery), blind loops, diverticula, strictures.
Medications: Opioids (slow motility), PPIs (reduce acid), frequent antibiotics (alter bacterial populations).
Ileocecal valve dysfunction: The valve between the small and large intestine may not close properly, allowing colonic bacteria to backwash.
Diabetes: Diabetic neuropathy impairs gut motility → SIBO.
Hypothyroidism: Slow motility → bacterial overgrowth.

Testing

Lactulose Breath Test (Most Common)

How it works:

Fast overnight (12 hours). Avoid high-fiber and high-sugar foods the day before.
Drink a lactulose solution (a sugar that humans cannot absorb).
Collect breath samples every 15-20 minutes for 3 hours.
Bacteria ferment the lactulose and produce gases that are absorbed into the blood and exhaled.

Interpreting Results

Hydrogen rise >20 ppm within 90 minutes: Hydrogen-dominant SIBO. Typically causes diarrhea.
Methane >10 ppm at any point: IMO (intestinal methanogen overgrowth). Methanogens (archaea, not bacteria) produce methane, which slows motility → constipation.
Hydrogen sulfide: Newer testing (trio-smart breath test) can now measure H2S. Causes diarrhea and distinctive rotten-egg gas.
Flat-line (no rise): May indicate hydrogen sulfide SIBO (H2S-producing bacteria consume hydrogen, keeping it low) or a false negative.

Treatment

Conventional Antimicrobials

Rifaximin (Xifaxan): The most studied SIBO antibiotic. Non-absorbed (works locally in the gut). 550mg 3x/day for 14 days. Well-tolerated. Insurance coverage can be difficult.
Rifaximin + Neomycin: For methane-dominant (IMO). Rifaximin alone is less effective against methanogens. Neomycin is added for 14 days. Alternatively, rifaximin + metronidazole.
For hydrogen sulfide: Bismuth subsalicylate (Pepto-Bismol, high dose) is sometimes used alongside rifaximin.

Herbal Antimicrobials

A 2014 Johns Hopkins study found herbal antimicrobials as effective as rifaximin for SIBO. Common protocols:

Oregano oil (emulsified) + berberine + neem
Allicin (garlic extract) — particularly effective against methanogens
Protocol: 4-6 weeks, higher dose than standard supplement use. Work with a knowledgeable practitioner.

Relapse Prevention (Critical)

Prokinetics: Medications or supplements that stimulate the MMC. Options: low-dose erythromycin (250mg at bedtime — antibiotic at sub-antibiotic dose acts as a prokinetic), prucalopride, or natural prokinetics (ginger, 5-HTP, Iberogast).
Meal spacing: 4-5 hours between meals to allow complete MMC cycles. No snacking.
Address root cause: Thyroid optimization, stop unnecessary PPIs, manage diabetes, treat adhesions if applicable.

🛒 SIBO Management Support

Digestive Enzymes — SIBO causes malabsorption because bacteria in the small intestine compete with you for nutrients. Enzymes ensure food is broken down and absorbed before bacteria can ferment it, reducing gas production and improving nutrient status.
Whey Protein — SIBO-related malabsorption often causes protein and calorie deficiency. An easily absorbed protein source ensures adequate nutrition while treating the overgrowth.
Daily Vitamin — SIBO specifically depletes B12, iron, and fat-soluble vitamins (A, D, E, K) through bacterial consumption and fat malabsorption. Comprehensive supplementation prevents and corrects these deficiencies.

Medical Disclaimer: This article is for educational purposes only. SIBO diagnosis and treatment should be managed by a gastroenterologist or functional medicine practitioner experienced with the condition. Do not self-treat with antibiotics. Dr. Adegbola is the founder of Casa de Sante.

Back to blog

Keto. Paleo. No Digestive Triggers. Shop Now

No onion, no garlic – no pain. No gluten, no lactose – no bloat. Low FODMAP certified.

Stop worrying about what you can't eat and start enjoying what you can. No bloat, no pain, no problem.

Our gut friendly keto, paleo and low FODMAP certified products are gluten-free, lactose-free, soy free, no additives, preservatives or fillers and all natural for clean nutrition. Try them today and feel the difference!