In our previous blog post, Beyond IBS: What Normal Test Results Don’t Tell You About Your Gut, we explored how standard medical tests often fail to detect key factors affecting gut health, such as microbiome imbalances, stress, diet, and lifestyle. Many individuals suffer from persistent bloating, gas, constipation, diarrhoea, and reflux without clear answers. One often-overlooked culprit behind these digestive struggles is Small Intestinal Bacterial Overgrowth (SIBO). The good news? Unlike IBS, SIBO can be accurately tested and effectively treated.

What is SIBO?

SIBO occurs when bacteria migrate and multiply in the small intestine—a region that typically contains very few bacteria. Normally, these microbes reside in the large intestine, where they ferment carbohydrates, producing hydrogen or methane gas as a byproduct. Since the small intestine isn’t designed for significant gas production, this leads to bloating, discomfort, and altered bowel movements.

The Three Main Types of SIBO:

• Hydrogen SIBO – Associated with diarrhea but can also cause alternating constipation and diarrhoea.
• Methane SIBO – Primarily linked to constipation.
• Hydrogen Sulfide SIBO – Characterised by a distinct rotten egg-smelling gas.

How Does SIBO Develop?

A healthy digestive tract maintains a delicate bacterial balance. SIBO disrupts this equilibrium when bacteria from the large intestine overgrow in the small intestine, often due to:

1. Impaired Migrating Motor Complex (MMC)

The MMC acts as a natural “housekeeping wave,” clearing bacteria from the small intestine. When it’s impaired, bacteria linger and overgrow. Conditions linked to MMC dysfunction:

• Gastroenteritis (parasites, bacteria, yeast infections)
• Clostridium difficile infections
• Inflammatory Bowel Disease (IBD)
• Scleroderma
• Diabetes
• Ehlers-Danlos Syndrome
• Hypothyroidism
• Medications (opiates, repeated antibiotic use)
• Surgery or nerve damage
• Post-infectious IBS caused by an acute stomach bug.
• Autonomic nervous system dysfunction (sympathetic dominance)

2. Structural Abnormalities

Altered anatomy can obstruct bacterial clearance or allow bacteria to migrate into the small intestine. Common causes:

• Adhesions or obstructions (e.g., from endometriosis or surgery)
• IBD strictures
• Ileocecal valve impairment or removal
• Volvulus (intestinal twisting)
• Cancer
• Superior Mesenteric Artery Syndrome
• Chronic constipation

3. Physiological Imbalances

Changes in stomach acid levels, bile flow, bowel motility, or enzyme production can allow bacterial overgrowth. Potential causes:

• Low stomach acid (hypochlorhydria)
• Altered bile flow and enzyme production
• Proton pump inhibitors (PPIs) 
• Immunodeficiency
• Medications that slow bowel motility such as opioids, antidepressants, iron supplements, NSAIDs, and diuretics
• Significant periods of stress or trauma 
• Head injury

Diet and SIBO: Is a Low FODMAP Diet the Answer?

Many IBS sufferers find relief on a low FODMAP diet, which reduces fermentable carbohydrates—the primary fuel for SIBO-related bacteria. However, this diet is not a long-term solution as it also starves beneficial gut bacteria, potentially leading to further imbalances. Effective SIBO treatment is essential to restore gut health without prolonged dietary restrictions.

How Common is SIBO in IBS Patients?

SIBO is a major underlying cause of IBS. While IBS affects about 15% of the global population, studies suggest that 60-80% of IBS cases are actually due to SIBO. This means millions of people may be unknowingly suffering from an undiagnosed, treatable condition.

Recognising SIBO Symptoms

SIBO symptoms closely resemble IBS, making diagnosis challenging. However, bloating is a key indicator. Common symptoms include: 

• Abdominal bloating and distension
• Cramping and pain
• Constipation and/or diarrhoea
• Excessive gas, belching, and flatulence
• Acid reflux
• Fat malabsorption (sticky, oily stools)
• Leaky gut symptoms (skin rashes, allergies, food intolerances)
• Nausea
• Systemic symptoms like fatigue, joint pain, headaches, and insomnia

Understanding the Three Types of SIBO

Each type of SIBO requires a specific treatment approach:

Methane-Dominant SIBO (SIBO-C) – Linked to constipation. Unlike other types, this isn’t caused by bacteria but by archaea, single-celled organisms that feed on hydrogen and produce methane, slowing digestion and worsening constipation.

Hydrogen-Dominant SIBO (SIBO-D) – The most common type, associated with diarrhoea. Carbohydrate-fermenting bacteria produce hydrogen gas, leading to bloating, pain, and loose stools.

Hydrogen Sulfide SIBO – Characterised by foul-smelling gas (rotten eggs). While there’s no direct test for this type, symptoms and negative results for other SIBO types often indicate its presence. Hydrogen sulfide can be particularly toxic to intestinal cells.

How SIBO Impacts Gut and Overall Health

SIBO doesn’t just cause digestive discomfort—it interferes with nutrient absorption and weakens overall health:

• Intestinal Damage: Bacterial byproducts damage the intestinal lining, affecting digestion and nutrient absorption.
• Nutrient Depletion: Bacteria consume essential nutrients like B12, magnesium, iron, calcium, and amino acids—impacting energy, brain function, and immunity.
• Malabsorption: Disruptions in digestion prevent proper nutrient absorption, weakening the body’s defenses.
• MMC Dysfunction: SIBO can impair the body's natural cleansing function, increasing relapse risk.

Final Thoughts

SIBO is a complex but treatable condition that often underlies IBS symptoms. If you suspect SIBO, proper testing is the next crucial step. In the IBS Protocol, we provide expert guidance on SIBO testing and treatment, along with addressing other common underlying causes, to help you restore balance and improve your digestive health.