The purpose is to test the relationship between abdominal pain symptoms and intestinal inflammation in two groups (overweight and normal weight patients with chronic abdominal pain of unknown origin). After obtaining informed consent, an initial screening history and physical exam to ensure eligibility will be performed. The participants abdominal pain, psychological distress, quality of life, socio-demographic, and co-morbidities will be assessed via questionnaires. Anthropometry, vital signs, and fasting blood work will be drawn at both of the two visits to the Clinical Center of the National Institutes of Health for clinical screening labs and research purposes.