Obesity, which is increasing day by day, has become a major public health problem. With regard to its treatment, both conventional methods-such as medical nutrition therapy, exercise, pharmacological treatment, behavior change therapy- and surgical methods applied with new techniques are becoming increasingly widespread in our country and in the world. To determine the pre-operative nutritional status of the patient and the postoperative nutritional follow-up are extremely important in order to prevent possible nutritional complications. The purpose of this review is to examine the preoperative and postoperative principles of bariatric surgical procedure.