Understanding the Different Types of Small Intestinal Bacterial Overgrowth (SIBO)

SIBO, or Small Intestinal Bacterial Overgrowth, is a growing health issue that affects many people. It occurs when bacteria overgrow in the small intestine, causing a range of uncomfortable and debilitating symptoms. SIBO can result from various underlying conditions and is classified into three distinct types: hydrogen-dominant SIBO, methane-dominant SIBO, and mixed-dominant SIBO. Each type presents unique symptoms and requires specific treatments. In this article, we will explore the different types of SIBO, their symptoms, and available treatments. With the right testing and approach, those with SIBO can find relief and lead healthier lives.

What is SIBO?

Small Intestinal Bacterial Overgrowth (SIBO) occurs when bacteria that normally reside in the large intestine start growing in the small intestine. This condition disrupts digestion, causing issues like abdominal pain, diarrhoea, and bloating. If left untreated, SIBO can lead to serious health problems, such as anaemia, liver disease, and symptoms related to a leaky gut. SIBO is classified into three main types: hydrogen-dominant, methane-dominant, and mixed-dominant, each with distinct symptoms and treatment approaches.

Hydrogen-Dominant SIBO

Hydrogen-dominant SIBO is the most common form, affecting about 60% of people with SIBO. It is caused by an overgrowth of bacteria that produce hydrogen gas, such as E. coli and Klebsiella pneumoniae. Common triggers include antibiotic use and gastrointestinal disorders. Diagnosis is typically done through hydrogen breath tests.

Methane-Dominant SIBO

Methane-dominant SIBO is less common, affecting about 25% of people with SIBO. It involves an overgrowth of bacteria that produce methane gas, such as Bacteroides species and Fusobacterium nucleatum. This type is more prevalent in individuals who have had gastrointestinal surgery. Diagnosis involves breath tests using substrates like lactulose and glucose.

Mixed-Dominant SIBO

Mixed-dominant SIBO involves bacteria that produce both hydrogen and methane gases. It is the second most common form of SIBO. Diagnosis is similar to the other types, using breath tests with lactulose or glucose.

Hydrogen Sulfide SIBO

Hydrogen sulfide SIBO is characterized by excessive production of hydrogen sulfide (H2S) in the small intestine. It is linked to digestive disorders like irritable bowel syndrome, leaky gut, and inflammatory bowel disease. Symptoms include abdominal pain, diarrhea, constipation, bloating, flatulence, and bad breath. Treatment options include antibiotics, herbal antimicrobials, probiotics, dietary changes, and lifestyle modifications. Consulting a functional medicine doctor is essential for personalized treatment.

Common Symptoms of SIBO

SIBO symptoms vary widely, making it challenging to diagnose. Common symptoms include:

Diagnosing SIBO

Various tests are available for diagnosing SIBO, including organic acids tests and microbiome testing (e.g., GI MAP, Genova, and Doctor’s Data). However, these tests primarily assess the large intestine. The gold standard for SIBO diagnosis is a breath test that measures different gas levels. At the Edinburgh Centre for Functional Medicine, we recommend both breath and microbiome tests, as SIBO often stems from a dysfunctional large intestine.

How We Can Help

If you experience digestive issues, fatigue, anxiety, depression, or other unexplained symptoms, contact the team at the Edinburgh Centre for Functional Medicine today.

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