Causes and Risk Factors

SIBO usually develops when normal defenses against bacterial overgrowth are disrupted. The goal is not only to reduce bacterial overgrowth, but also to understand why it occurred.

Normal Protective Mechanisms

The small intestine is protected by:

• coordinated intestinal motility
• stomach acid
• bile and pancreatic enzymes
• the ileocecal valve
• normal intestinal anatomy
• immune function

Disruption of these mechanisms can allow bacteria to accumulate in the small intestine.

Motility Disorders

Reduced intestinal motility can increase risk. Examples include:

• diabetes-related autonomic dysfunction
• scleroderma or other connective tissue disease
• gastroparesis
• intestinal pseudo-obstruction
• chronic opioid exposure
• other medications that slow motility

Anatomic Risk Factors

Structural changes can predispose to bacterial stasis. These include:

• prior bowel surgery
• blind loops
• strictures
• adhesions
• fistulas
• small bowel diverticula
• altered ileocecal valve function

Digestive and Immune Conditions

Other associated conditions may include:

• chronic pancreatitis
• pancreatic exocrine insufficiency
• cirrhosis
• immune deficiency
• celiac disease
• inflammatory bowel disease
• radiation enteritis

Medication Contributors

Some medications may contribute indirectly by altering motility, acidity, or microbial ecology. This does not mean they should be stopped without medical advice.

Discuss medication concerns with a clinician, especially if you take acid suppression, opioids, anticholinergic medications, or repeated antibiotics.

Idiopathic Symptoms

Some patients have symptoms suggestive of SIBO without a clear cause. In that situation, clinicians should avoid premature closure and consider a broader differential diagnosis.