Bariatric Medicine: The discipline concerned with WEIGHT REDUCTION in patients with OBESITY.Bariatric Surgery: Surgical procedures aimed at affecting metabolism and producing major WEIGHT REDUCTION in patients with MORBID OBESITY.Obesity, Morbid: The condition of weighing two, three, or more times the ideal weight, so called because it is associated with many serious and life-threatening disorders. In the BODY MASS INDEX, morbid obesity is defined as having a BMI greater than 40.0 kg/m2.Gastric Bypass: Surgical procedure in which the STOMACH is transected high on the body. The resulting small proximal gastric pouch is joined to any parts of the SMALL INTESTINE by an end-to-side SURGICAL ANASTOMOSIS, depending on the amounts of intestinal surface being bypasses. This procedure is used frequently in the treatment of MORBID OBESITY by limiting the size of functional STOMACH, food intake, and food absorption.Gastroplasty: Surgical procedures involving the STOMACH and sometimes the lower ESOPHAGUS to correct anatomical defects, or to treat MORBID OBESITY by reducing the size of the stomach. There are several subtypes of bariatric gastroplasty, such as vertical banded gastroplasty, silicone ring vertical gastroplasty, and horizontal banded gastroplasty.