I disagree with the idea of training both types of muscle fibers. Fast-twitch fibers have the greatest potential for size and strength, so why wouldn't you want all of your fibers to be fast-twitch?
Whenever you do cardio, or long distance running, etc., you are converting fast-twitch fibers to slow-twitch. That's why you will rarely see a powerlifter doing any sort of cardio. IMO, for both the powerlifter and bodybuilder, the best way to go for fat loss without sacrificing the fast-twitch fibers is to do high-intensity interval training.