🦠 Small Intestinal Bacterial Overgrowth (SIBO)

Understanding, diagnosing, and treating bacterial overgrowth in the small intestine

Last reviewed: February 2026

Bacteria Overgrowth Small Intestine with SIBO
📊 Up to 80% Of IBS patients may have SIBO
🦠 Bacterial Excess bacteria in small bowel
💨 Gas & Bloating Main symptoms
✅ Treatable With antibiotics/herbs

📖 What is SIBO?

Small Intestinal Bacterial Overgrowth (SIBO) is a condition characterized by an abnormal increase in the number of bacteria in the small intestine, particularly types of bacteria that normally live in the large intestine (colon).

The small intestine normally has relatively few bacteria compared to the colon. Several mechanisms keep bacterial levels low:

When these protective mechanisms fail, bacteria can overgrow in the small intestine. These bacteria ferment carbohydrates, producing gas and causing symptoms. They can also interfere with nutrient absorption.

Types of SIBO: SIBO is categorized by the type of gas produced - hydrogen-dominant (more common), methane-dominant (now called Intestinal Methanogen Overgrowth or IMO), or hydrogen sulfide-dominant. Each type may have different symptoms and treatments.

🔬 Causes & Risk Factors

SIBO develops when protective mechanisms are compromised:

Structural/Anatomical Causes

Motility Disorders

Reduced Gastric Acid

Other Risk Factors

Common Underlying ConditionWhy It Causes SIBO
Food poisoning historyDamages nerves controlling MMC; produces anti-vinculin antibodies
Long-term PPI useReduces gastric acid barrier
DiabetesDamages nerves affecting gut motility
IBSUnderlying motility disturbance
HypothyroidismSlows gut motility
Adhesions from surgeryCreates pockets where bacteria accumulate

🚨 Symptoms

SIBO symptoms overlap significantly with IBS, which is why many IBS patients may actually have underlying SIBO.

Common Symptoms

Symptoms of Nutrient Malabsorption

SIBO Type and Symptoms

TypeGas ProducedTypical Symptoms
Hydrogen SIBOHydrogen (H2)Diarrhea, urgency, bloating
Methane SIBO (IMO)Methane (CH4)Constipation, bloating, hard stools
Hydrogen Sulfide SIBOHydrogen sulfide (H2S)Diarrhea, rotten egg gas, sulfur burps

🔍 Diagnosis

Breath Testing

The most common non-invasive test for SIBO. Patient drinks a sugar solution (lactulose or glucose), and breath samples are collected to measure hydrogen and methane gas production.

Types of Breath Tests

Preparation for Breath Test

Interpreting Results

Other Diagnostic Methods

Limitations: Breath testing has limitations and false negatives can occur. Clinical judgment is important, and some practitioners treat empirically based on symptoms.

💊 Treatment

SIBO treatment typically involves antimicrobial therapy, dietary modifications, and addressing underlying causes.

Pharmaceutical Antibiotics

SIBO TypeFirst-Line AntibioticDuration
Hydrogen SIBORifaximin (Xifaxan)14 days
Methane SIBO (IMO)Rifaximin + Neomycin or Metronidazole14 days
Hydrogen SulfideBismuth + other agentsVaries

Rifaximin advantages: Non-absorbed (stays in gut), well-tolerated, targets gut bacteria specifically, low resistance development.

Herbal Antimicrobials

Some practitioners use herbal protocols, which studies show can be as effective as rifaximin:

Elemental Diet

A liquid diet of pre-digested nutrients that starves bacteria by being absorbed quickly in the upper small intestine. Very effective (85% success in 2 weeks) but difficult to follow. May be used for difficult cases.

Treatment Success Rates

🥗 Diet Strategies

Diet plays an important role in managing SIBO symptoms and preventing recurrence.

Low-FODMAP Diet

Reduces fermentable carbohydrates that feed bacteria. Often used during and after treatment to reduce symptoms.

Specific Carbohydrate Diet (SCD)

Eliminates complex carbohydrates and polysaccharides that bacteria ferment. More restrictive than low-FODMAP.

SIBO-Specific Diets

General Dietary Principles

Timing: Restrictive diets are typically used short-term during treatment. Long-term restriction can lead to nutritional deficiencies and reduced quality of life. Work with a dietitian to reintroduce foods safely.

🔄 Preventing Recurrence

Recurrence is a major challenge in SIBO management. Prevention strategies include:

Prokinetics

Medications that improve gut motility and restore the MMC:

Address Underlying Causes

Lifestyle Measures

❓ Frequently Asked Questions

Is SIBO the same as IBS?

No, but they are related. SIBO is a specific condition with excess bacteria in the small intestine. IBS is a functional disorder with no identifiable cause. However, studies suggest up to 80% of IBS patients may have SIBO. Treating SIBO can improve IBS symptoms in many cases.

Can probiotics cause or treat SIBO?

This is debated. Some practitioners avoid probiotics during SIBO treatment as they add more bacteria. Others find certain strains helpful. Soil-based probiotics may be better tolerated. After treatment, specific probiotics may help prevent recurrence.

Why does SIBO keep coming back?

Recurrence is common because the underlying cause (impaired motility, anatomical issues, etc.) often persists. Using prokinetics, addressing root causes, and maintaining good meal hygiene can reduce recurrence. Some patients need periodic "maintenance" treatment.

How long does treatment take?

Antibiotic treatment is typically 2 weeks. However, many patients need multiple rounds. Including prevention strategies and dietary optimization, the full treatment process often takes several months. Maintenance continues long-term.