SIBO Guide: Understanding and Managing Small Intestinal Bacterial Overgrowth

Small Intestinal Bacterial Overgrowth (SIBO) is a condition where bacteria that normally reside in the large intestine migrate and proliferate in the small intestine. This overgrowth disrupts normal digestion, damages the intestinal lining, and produces excessive gas — leading to symptoms that often mirror or overlap with IBS. Understanding SIBO is essential for effective management and long-term gut health.

What Is SIBO?

The small intestine is designed to have relatively low bacterial counts compared to the colon. When bacteria from the large intestine colonize the small intestine in excessive numbers, they begin fermenting food before it is properly absorbed. This premature fermentation causes bloating, abdominal pain, diarrhea or constipation, and nutritional deficiencies.

SIBO is increasingly recognized as an underlying cause of IBS symptoms in a significant percentage of patients. Studies suggest that up to 78% of people diagnosed with IBS may have SIBO as a contributing factor.

The Three Types of SIBO

The type of SIBO you have depends on which gases the overgrown bacteria produce. Each type has distinct symptoms and treatment considerations.

Hydrogen-Dominant SIBO

Hydrogen-producing bacteria ferment carbohydrates rapidly, generating hydrogen gas. This type is most commonly associated with diarrhea-predominant symptoms, urgency, and cramping. Hydrogen SIBO often responds well to the antibiotic rifaximin and tends to have the most straightforward treatment path.

Methane-Dominant SIBO (IMO)

Now more accurately called Intestinal Methanogen Overgrowth (IMO), this type involves archaea (not technically bacteria) that consume hydrogen and produce methane. Methane slows gut motility, making constipation the hallmark symptom. Patients often experience significant bloating, straining, and incomplete evacuation. Treatment typically requires a combination of rifaximin and neomycin or metronidazole.

Hydrogen Sulfide SIBO

The most recently identified type, hydrogen sulfide SIBO, involves bacteria that produce hydrogen sulfide gas. Symptoms can include diarrhea, foul-smelling gas, and sensitivity to sulfur-rich foods like eggs, cruciferous vegetables, and garlic. Testing for hydrogen sulfide SIBO has become available through newer breath test technologies like the trio-smart test.

How SIBO Is Diagnosed

Lactulose Breath Test

The most common diagnostic tool is the lactulose breath test. You drink a lactulose solution and then provide breath samples at regular intervals over 2 to 3 hours. The test measures hydrogen and methane (and in newer tests, hydrogen sulfide) levels in your breath. A rise in gas levels within the first 90 minutes suggests bacterial overgrowth in the small intestine.

Glucose Breath Test

The glucose breath test works similarly but uses glucose instead of lactulose. It is considered more specific (fewer false positives) but less sensitive (may miss distal SIBO) because glucose is absorbed quickly in the upper small intestine.

Interpreting Results

A positive breath test combined with clinical symptoms is typically sufficient for diagnosis. However, breath tests are not perfect — false negatives can occur, and some practitioners may treat based on clinical presentation alone when suspicion is high.

Treatment Approaches

SIBO treatment generally follows a phased approach, and recurrence is common, making ongoing management strategies critical.

Phase 1: Antimicrobial Treatment

The first line of treatment involves reducing the bacterial overgrowth. This can be accomplished through pharmaceutical antibiotics (rifaximin being the most studied) or herbal antimicrobials (such as berberine, oregano oil, and neem). Treatment duration is typically 2 to 4 weeks, and some patients require multiple rounds.

Phase 2: Dietary Management

During and after antimicrobial treatment, dietary management plays a crucial role. The low-FODMAP diet is frequently recommended because it reduces the fermentable substrates that feed the overgrown bacteria. Specific approaches include:

• Low-FODMAP diet — Limits fermentable carbohydrates that feed bacteria
• Bi-Phasic Diet — A SIBO-specific protocol developed by Dr. Nirala Jacobi
• Specific Carbohydrate Diet (SCD) — Eliminates complex carbohydrates
• Elemental diet — A liquid-only approach that starves bacteria while nourishing the patient

Understanding which foods are high and low in FODMAPs is critical during this phase. Our FODMAP Food Guide provides detailed breakdowns of individual foods, and the FODMAP Reference Database offers comprehensive food lists by category.

Phase 3: Prevention and Prokinetics

Preventing SIBO recurrence requires addressing the underlying causes. Prokinetic agents (both pharmaceutical and natural) help maintain the migrating motor complex (MMC), the cleansing wave that sweeps bacteria out of the small intestine between meals. Meal spacing of 4 to 5 hours between eating allows the MMC to function properly.

Dietary Management for SIBO Patients

Managing your diet with SIBO requires careful attention to both FODMAP content and overall meal composition. Key strategies include:

• Limit high-FODMAP foods during active treatment — garlic and onion are particularly important to avoid
• Choose safe starches like rice and potatoes as your carbohydrate base
• Be cautious with dairy — lactose-containing milk can worsen symptoms, but hard cheeses may be tolerated
• Space meals appropriately to support the migrating motor complex
• Consider low-FODMAP sweeteners instead of honey or agave

FODMAPSnap is particularly useful for SIBO patients because it provides instant FODMAP analysis of meals, taking the guesswork out of dietary management during what can be a stressful and confusing treatment period. The app includes dedicated SIBO profile support, allowing you to tailor recommendations to your specific SIBO type.

When to See a Doctor

SIBO shares symptoms with many other conditions, including celiac disease, inflammatory bowel disease, and pancreatic insufficiency. If you experience persistent digestive symptoms, unexplained weight loss, or nutritional deficiencies, it is important to work with a gastroenterologist or integrative medicine practitioner experienced in SIBO.

Related Resources

• IBS & SIBO Education — Understanding the connection between IBS and SIBO
• FODMAP Food Guide — Complete guide to FODMAP-friendly foods
• FODMAP Tracker Guide — How to track symptoms during SIBO treatment

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This article is for informational purposes only and does not constitute medical advice. SIBO diagnosis and treatment should be managed by a qualified healthcare provider. Do not start or stop any medications or supplements without consulting your doctor.