Small intestine bacterial overgrowth (SIBO) occurs when there are too many bacteria in the small intestine. Normally, most bacteria live in the large intestine. Causes of SIBO include low stomach acid, slow-moving digestion, structural problems in the intestines, and the overuse of certain medications. Risk factors include age, previous abdominal surgeries, and certain medical conditions. Symptoms of SIBO can include bloating, diarrhea, constipation, and nutrient deficiencies. Diagnosis often involves breath tests or endoscopy. Treatment typically includes antibiotics to reduce bacterial growth, dietary changes, and sometimes supplements or probiotics to support gut health. In severe cases, surgery may be needed. Without treatment, complications such as malnutrition, vitamin deficiencies, and osteoporosis may occur.