It is when you eat more calories than your body needs that you begin to put on extra weight. Exercise increases your body's need for calories. Exercise helps you lose weight by burning off calories. In addition, exercise increases the rate at which your body burns calories even when you aren't exercising. The reason for this is you body builds up muscle mass at the same time it is reducing body fat.
Muscle cells use more energy then fat cells.
Even though exercise uses up lots of calories, you will get the best results when you combine exercise with a sensible food plan. It takes a lot of exercise to burn enough calories to make a difference. To lose one pound of body fat, the average person must use up 3,500 calories. Trying to burn 500 calories every day for one week to lose just 1 pound of body weight for most people is unrealistic. You have just lost a pound in a healthy way.