Just because you lift weights, it does not mean that you are going to get big and bulky. In order to stimulate your metabolism, you need to put on some new muscle because they require calories for maintenance. When you start to atrophy (muscle shrinks), less calories are required to maintain it. When that happens, your metabolism slows down and when you increase your caloric intake over how much expend, you will start to gain fat. Muscle is good for you, it needs to be fed, it likes to burn calories, which in turn is a positive. A body with great muscle tone is not a bad thing!
Oregon Personal Trainer