The short answer to this question is yes. Most importantly, exercise can help keep weight off in the long term. Exercise can help you manage your weight in two ways:
Much of the weight re-gain that people experience after dieting is due to the metabolism slowing down and the loss of muscle that occurs. In general terms – if you lose muscle, your metabolism will slow down. This is why ‘quick fix’ weight-loss diets are ineffective in the long-term. People who diet without exercising will almost always put all the weight back on; some may even gain extra weight.
Exercise increases your lean muscle mass. Muscle weighs more than fat so it is possible that your weight could actually increase in the short-term following exercise. In which case, do not be disheartened – you need to stop thinking in terms of body weight and start thinking in terms of fitness body composition* which are much more important.
*Body composition is the amount of lean muscle tissue in the body in comparison to the amount of fat.