The BMI is defined as the body weight (in kilograms), divided by the square of the height (in meters). The result is expressed as a number in units of kilograms per square meter. In healthy adults, BMI ranges from 18.5 to 24.9, with a BMI above 30 being considered obese, and a BMI less than 18.5 considered underweight. The Consensus Panel of the National Institutes of Health (NIH) recommended the following criteria for consideration of bariatric surgery, including gastric bypass procedures: people who have a BMI of 40 or higher people with a BMI of 35 or higher with one or more related comorbid conditions The Consensus Panel also emphasized the necessity of multidisciplinary care of the bariatric surgical patient by a team of physicians and therapists to manage associated comorbidities and nutrition, physical activity, behavior, and psychological needs. The surgical procedure is best regarded as a tool that enables the patient to alter lifestyle and eating habits, and to achieve effective and permanent management of obesity and eating behavior. Since 1991, major developments in the field of bariatric surgery, particularly laparoscopy, have outdated some of the conclusions of the NIH panel. In 2004 the American Society for Bariatric Surgery (ASBS) sponsored a consensus conference which updated the evidence and the conclusions of the NIH panel. This conference, composed of physicians and scientists of both surgical and non-surgical disciplines, reached several conclusions, including: bariatric surgery is the most effective treatment for morbid obesity gastric bypass is one of four types of operations for morbid obesity laparoscopic surgery is equally effective and as safe as open surgery patients should undergo comprehensive preoperative evaluation and have multi-disciplinary support for optimum outcome Surgical techniques The gastric bypass, in its various forms, accounts for a large majority of the bariatric surgical procedures performed. It is estimated that 200,000 such operations were performed in the United States in 2008. Laparoscopic surgery is performed using several small incisions, or ports: one to insert a surgical telescope connected to a video camera, and others to permit access to specialized operating instruments. The surgeon views the operation on a video screen. Laparoscopy is also called limited access surgery, reflecting the limitation on handling and feeling tissues and also the limited resolution and two-dimensionality of the video image. With experience, a skilled laparoscopic surgeon can perform most procedures as expeditiously as with an open incision—with the option of using