Eating well is over half of your success in this gym. If you're training your ass off and are not paying attention to what you're fueling your body then you are pretty much not maximizing your time involved. Fitness is really two parts. One part is training. Place stress on the body and in return the body will adapt to those stressors and become stronger, better, and fitter.
The second part is recovery.
This is composed of both diet and sleep. Lack in either department will put a serious damper on your success in the gym. Here we will address the issue of diet and our stance on what and how much you should be fueling with.