Originally Posted by big

Absolutely. Diet is the key to bodyfat reduction.

If you're looking to gain mass and shed fat at the same time, take a read of some of the carb cycling posts that guys like Tom B and Paul S. If you're wanting to do both simultaneously (which is actually a good idea IMO assuming you're relatively lean already and have some reasonable mass behind you), you want to get yourself into calorie surplus by adding carbs around the times you train (especially right afterwards), but remain in a slight deficit the rest of the time. In effect, this is a timed carb diet.