Gastric bypass surgery weight loss results can vary, but most people will lose weight quickly over the 12 months following surgery. Typically people see about one-third of their excess weight lost over the next one to four years. The second year post-surgery shows the most dramatic improvements, not only with weight loss, but with improved health and quality of life. A weight loss of 65 to 80 percent of excess body weight is common, especially when the prescribed diet and exercise plan are followed.