A person puts on weight when the calories consumed are more than those spent in activity. Thus, there are ONLY two ways of losing weight a) reduction in the number of calories consumed and b) increase in the expenditure of calories by way of regular exercise. Most people who are slightly heavier than their ideal weight may be able to lose that weight by dietary changes and exercise. Some people may also be prescribed drugs that reduce the appetite and promote weight loss. Weight loss through dieting and exercise requires significant motivation on part of a person and is often difficult to sustain in the long term. It is possible to lose around 10-15% of the body weight and maintain it by disciplined eating and regular exercise. For most people, however, the lost weight comes back on sooner or later.
People who weigh significantly more than their normal weight may not be able to lose enough weight by dietary discipline and exercising alone. Also, it is harder for this group to maintain the lost weight. For example, a person whose ideal weight is 80kg but weighs 120 kg is carrying 40 kg of excess weight (EW). It may be hard for this person to maintain a reasonably low calorie diet and exercise enough to lose weight. This person may lose 10-12kg through sustained effort but losing 40kg is an almost impossible task. The heavier a person, more is the likelihood that he will have some joint / back problems that restrict his ability to exercise regularly and vigorously. Thus such a person may lose a few kilograms and put them back on (or more) over the next few years. It is well known that when a person loses weight both fat (2/3) and muscle mass (1/3) is lost, but when the weight is regained it is purely in the form of fat. Thus with multiple cycles of such a “yo-yo” weight loss and weight gain over years a person may end up losing significant muscle mass at the cost of accumulating fat. This has serious health implications.
For people who are severally obese, weight loss or bariatric surgery is the only proven way of achieving significant and long-lasting weight loss. The success of weight loss surgery is determined by looking at the amount of excess weight lost (EWL) at two years, and maintained in the long term. Excess weight is the weight a person carries in addition to their ideal weight. For example if a person weighs 150kg and his ideal weight is 100kg, then the excess weight is 50kg. Now, if he loses weight and weighs115kg he will have lost 35kg (out of the 50kg excess weight) Thus the EWL is 35kg out of 50kg or 70%. Within two years of weight loss surgery a person loses 60-75% of the excess weight (depending on the type of surgery) and maintains around 50-65% EWL at 8-10 years after surgery. With disciplined eating and regular exercise (which becomes easier once significant weight is lost) a person may even lose more weight than this and maintain the loss.