All participants will undergo a standard 48 hour gastrointestinal transit measurement using scintigraphy with standardized meals during the first 12 hours. The response endpoints (colonic geometric center at 4 h, colonic geometric center at 24 h, colonic geometric center at 48 h, gastric residual at 2 & 4 h, colonic filling at 6 h and ascending colonic emptying t1/2) will be based on abdominal scintigraphic images following the technetium-99m egg meal and methacrylate-coated, delayed-release capsule containing 111In labeled activated charcoal.