I have to disagree. The more muscle you build, the more weight you CAN lose. Muscle is where the calories are burned, so weight work in the gym will pay big benefits in weight loss. Yes muscle is heavier than fat, but it doesn't have to put weight on you in the long run. Now if you are slim and are adding muscle, yes you will be adding weight. Who care about that anyway. It's not problem. But if you are exchanging fat for muscle, you will likely lose weight due to the amount of fat lost when a little muscle starts to do its magic.