Most Common Causes of SIBO: Why It Happens and What Favors It
Small Intestinal Bacterial Overgrowth (SIBO) doesn’t usually appear out of nowhere — it develops when the normal balance and movement of the small intestine are disrupted. Understanding the causes can help you prevent flare-ups and support long-term digestive health.
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What Causes SIBO?
SIBO occurs when bacteria that normally live mainly in the large intestine begin to grow excessively in the small intestine, where they interfere with digestion and nutrient absorption.
1. Impaired Intestinal Motility
When the small intestine doesn’t move food and waste along properly, bacteria can linger and multiply. This can happen with conditions that slow down gut movement, such as diabetes, nerve dysfunction, or motility disorders.
2. Structural Abnormalities or Surgical Changes
Certain anatomical issues — like scar tissue, diverticula (pouches), or changes after abdominal surgery — can create pockets where bacteria accumulate instead of moving through the gut.
3. Dysfunction of the Ileocecal Valve
The ileocecal valve separates the small intestine from the colon. If it doesn’t function properly, bacteria from the large intestine can migrate backward into the small intestine, promoting overgrowth.
4. Reduced Stomach Acid or Digestive Defenses
Low stomach acid — which can be caused by long-term use of acid-reducing medications like proton pump inhibitors, aging, or other factors — may mean bacteria are not killed off effectively, increasing the chance of overgrowth.
5. Medical Conditions That Affect Gut Function
Conditions such as Crohn’s disease, celiac disease, scleroderma, and other inflammatory or motility-related disorders can change how the gut functions and raise the risk of SIBO.
6. Antibiotic Use and Microbiome Disruption
Frequent or prolonged use of antibiotics can disrupt the balance of gut bacteria, reducing beneficial microbes and giving room for others to overgrow in the small intestine.
7. Other Risk Factors
Other factors that may contribute include:
Aging, which can reduce natural digestive defense mechanisms
Chronic alcohol use
Conditions that weaken immune function
Repeated periods of constipation or slow transit
Some of these allow bacteria to stay in the small intestine longer than they should, creating a favorable environment for overgrowth.
Why This Matters
Recognizing the underlying causes of SIBO can help you and your healthcare provider build a targeted approach — not just masking symptoms, but addressing the factors that allow bacterial overgrowth to develop in the first place.