Small Intestinal Bacterial Overgrowth (SIBO) is a misunderstood digestive disorder in which excessive bacteria colonize the small intestine—an area meant to contain 100 to 1,000 times fewer bacteria than the colon. When too many bacteria settle where they don’t belong, they interfere with digestion, produce excess gas, trigger inflammation, and cause nutrient deficiencies. Because symptoms mimic common digestive disorders, many people struggle for years without answers.

Understanding the Small Intestine’s Role

Before symptoms make sense, it’s important to understand how the small intestine works.

The small intestine is responsible for:

• Breaking down food with enzymes

• Absorbing nutrients into the bloodstream

• Moving food forward with rhythmic contractions (peristalsis)

• Preventing colon bacteria from migrating upward

When this system slows down or becomes damaged, bacteria multiply rapidly.

Main Causes of SIBO (Expanded)

1. Motility Disorders: The #1 Root Cause

Healthy motility sweeps bacteria downward into the colon. When slowed, bacteria stagnate and multiply.

Common causes include:

• Diabetes (affects nerve supply to the gut)

• Hypothyroidism (slows metabolism and gut movement)

• Scleroderma and connective tissue diseases

• Chronic opioid use

• Post-infectious IBS

Even mild motility issues can trigger SIBO.

2. Anatomical or Structural Problems

Any structural change that traps food allows bacteria to overgrow:

• Adhesions after abdominal surgery

• Diverticula in the small intestine

• Crohn’s strictures

• Partial obstructions

• Bowel loops that fold abnormally

These pockets become perfect bacterial “homes.”

3. Low or Absent Stomach Acid

Stomach acid kills harmful bacteria before they enter the intestines. When acid is low due to:

• Long-term PPI use

• H. pylori infection

• Autoimmune atrophic gastritis

• Aging

bacteria survive and migrate downward.

4. Liver, Gallbladder, or Pancreas Dysfunction

Bile and enzymes suppress bacterial growth. Impairment leads to:

• Poor fat digestion

• Food stagnation

• Increased fermentation

Making SIBO more likely.

5. Repeated or Long-Term Antibiotics

Paradoxically, certain antibiotics disrupt the colon’s microbiome so severely that opportunistic bacteria invade the small intestine.

Signs and Symptoms (Expanded, More Detailed)

1. Severe, Recurrent Bloating

Often within 30 minutes of eating, unlike IBS which may occur hours later.
Many patients report looking “6 months pregnant.”

2. Excessive Gas and Belching

Hydrogen or methane-producing bacteria ferment carbohydrates aggressively.
Methane-producing bacteria are strongly tied to constipation-dominant SIBO.

3. Alternating Diarrhea and Constipation

Some patients swing between both depending on which bacteria dominate.

4. Malabsorption Symptoms

Bacteria compete for nutrients, leading to:

• Low B12

• Iron deficiency

• Weight loss

• Protein deficiency

• Fat malabsorption (greasy, floating stools)

5. Neurological Symptoms

Often ignored but common:

• Brain fog

• Memory issues

• Difficulty concentrating

• Tingling in hands and feet

These arise from vitamin deficiencies and toxin buildup.

6. Food Intolerances

Patients may suddenly react to:

• Dairy

• Gluten

• High-fiber foods

• Sugars

• FODMAP-rich fruits and vegetables

Because bacteria ferment these foods excessively.

7. Skin Conditions

Linked to systemic inflammation:

• Rosacea

• Acne

• Eczema

• Hives

Many improve after treating SIBO.

Complications of Untreated SIBO (Expanded)

Chronic SIBO may lead to:

• Leaky gut

• Worsening IBS symptoms

• Severe nutrient deficiencies

• Weight loss and muscle wasting

• Fat-soluble vitamin deficiencies (A, D, E, K)

• Bone density loss

• Chronic fatigue syndrome

• Worsening autoimmune disease