SIBO

A Comprehensive Overview by Dr Paul Froomes MD

Small Intestinal Bacterial Overgrowth (SIBO) is a condition where an abnormal number and/or types of bacteria proliferate in the small intestine, leading to various gastrointestinal symptoms and systemic effects. In a healthy individual, the small intestine contains relatively few bacteria compared to the colon. However, certain factors can lead to bacterial overgrowth in the small intestine, which can interfere with nutrient absorption and cause a wide range of symptoms.

Causes of SIBO
Several factors can contribute to the development of SIBO:

1. Impaired Motility: Conditions such as irritable bowel syndrome (IBS), diabetes, and scleroderma may result in impaired motility of the small intestine. This reduced movement allows bacteria to remain in the small intestine for prolonged periods, promoting overgrowth.

2. Anatomical Abnormalities: Structural changes, such as strictures, adhesions, or diverticula in the small intestine, can lead to stagnation of intestinal contents, facilitating bacterial overgrowth.

3. Hypochlorhydria: Reduced stomach acid production (hypochlorhydria), often due to long-term use of proton pump inhibitors (PPIs) or chronic conditions like gastritis, can allow for bacterial overgrowth in the small intestine.
Immune Deficiency: A weakened immune system, either from conditions like HIV or immunosuppressive medications, can impair the body’s ability to regulate bacterial growth in the gut.

4. Disrupted Gut Microbiota: Antibiotic overuse or an unbalanced diet can disturb the natural bacterial populations in the gut, potentially leading to SIBO.
Post-surgical Alterations: Individuals who have undergone certain abdominal surgeries, such as gastric bypass, may be at a higher risk of SIBO due to alterations in gut structure and function.

Symptoms of SIBO
SIBO presents a range of gastrointestinal and systemic symptoms, some of which can be quite vague or overlap with other conditions like IBS:

Bloating: One of the most common symptoms, often described as feeling like the abdomen is distended or full of gas.
Abdominal pain and cramping: Discomfort that may fluctuate in intensity, usually post-meal.
Diarrhea or constipation: Patients can experience alternating bowel habits, although diarrhea is more common.
Malabsorption: This can lead to deficiencies in fat-soluble vitamins (A, D, E, K) and minerals like calcium and iron, which may result in fatigue, weight loss, and weakness.
Steatorrhea: Fatty, foul-smelling stools may occur due to fat malabsorption.
Brain fog: Cognitive impairment or difficulty concentrating is reported by many SIBO patients.
Nutritional deficiencies: Vitamin B12 deficiency and iron deficiency anemia are common due to impaired absorption.
Bacterial Subtypes in SIBO: Hydrogen, Methane, and Hydrogen Sulfide
SIBO can be further classified based on the type of gas-producing bacteria that dominate the overgrowth. These gases can be measured via breath testing, and understanding the type of gas produced is crucial for tailoring treatment protocols.

Type 1 – Hydrogen-Producing Bacteria:
These bacteria ferment carbohydrates into hydrogen gas, leading to symptoms like bloating, diarrhea, and malabsorption. The overproduction of hydrogen is more common in SIBO related to IBS-D (diarrhea-predominant IBS).
Treatment: Rifaximin is the antibiotic of choice for hydrogen-dominant SIBO, with a typical dosage of 550 mg three times daily for 14 days .

Type 2 – Methane-Producing Archaea (IMO):
Methanogens convert hydrogen gas into methane, which is associated with constipation rather than diarrhea. Methane-producing SIBO (often referred to as intestinal methanogen overgrowth, or IMO) tends to cause slow bowel movements and constipation.
Treatment: Rifaximin combined with neomycin is effective for methane-dominant SIBO. Neomycin targets methanogens, while rifaximin addresses the other bacteria. The standard dosage is 550 mg rifaximin twice daily plus 500 mg neomycin twice daily for 10–14 days .

Type 3 – Hydrogen Sulfide-Producing Bacteria:
Hydrogen sulfide-producing bacteria are less common but can be detected via specific breath tests. These bacteria are linked to diarrhea, abdominal pain, and systemic symptoms like fatigue and malaise. Hydrogen sulfide has a distinct “rotten egg” odor and may contribute to malodorous flatulence.
Treatment: There is limited data on the most effective treatment for hydrogen sulfide SIBO, but some evidence supports the use of bismuth-containing compounds (e.g., bismuth subsalicylate) and antibiotics like metronidazole or amoxicillin-clavulanate .