Causes

Small intestinal bacterial overgrowth (SIBO) can be caused by:

• Complications of abdominal surgery, including gastric bypass for obesity and gastrectomy to treat peptic ulcers and stomach cancer
• Structural problems in and around your small intestine, including scar tissue (intestinal adhesions) that can wrap around the outside of the small bowel, and bulging pouches of tissue that protrude through the wall of the small intestine (intestinal diverticulosis)
• Certain medical conditions, including Crohn's disease, radiation enteritis, scleroderma, celiac disease, diabetes or other conditions that can slow movement (motility) of food and waste products through the small intestine

Why small intestinal bacterial overgrowth (SIBO) develops

The small intestine is the longest section of your digestive tract, measuring about 20 feet (6.1 meters). The small intestine is where food mixes with digestive juices and nutrients are absorbed into your bloodstream.

Unlike your large intestine (colon), your small intestine normally has relatively few bacteria due to rapid flow of contents and the presence of bile. But in SIBO, stagnant food in the bypassed small intestine becomes an ideal breeding ground for bacteria. The bacteria may produce toxins as well as interfere with the absorption of nutrients. The breakdown products following bacterial digestion of food can also trigger diarrhea.