Gastroenterologists have extensive training in the diagnosis and treatment of conditions that affect the esophagus, stomach, small intestine, large intestine (colon), and biliary system (e.g., liver, pancreas, gallbladder, bile ducts). Gastroenterology is a subspecialty of internal medicine. Gastroenterologists have a thorough understanding of how food moves through the digestive tract (called motility) and the physical and chemical break down of food (digestion), including the absorption of nutrients and the removal of waste products.