Regular exercise is as important as eating regularly. Just like there is a such thing as being mal or undernutritioned, there is also a such thing as being overnutritioned which converts to being overweight. Over nutrition coverts to being overweight because the body uses the nutrients in the amounts that it needs and stores the rest as fat.
However, when you are active in exercise, the stored fat is used as energy and therefore burned. You have to move as much or more than you eat to maintain a healthy lifestyle.