Ultimately, the QUALITY OF YOUR AMINO ACIDS will determine your rate of growth. If you think Taco Bell and McDonalds will build muscle-tissue, YOUR'E WRONG!
I eat primarily egg, beef, chicken, turkey, fish, and dairy, with all of my carbohydrates coming from oats, yams, and select fruits and lots of vegetables. All of my fats are from natural animal sources, limited dairy, eggs, and some nuts.
I eat approximately 700-1,000 calories per meal, and I eat every 2-3 hours--no exeptions. I never even have to force-feed, since I have been eating like this for over 10 years. I get very hungry, very often. My body NEEDS the nutrients. I have an extremely fast metabolism and a very ectomorphic skeleton.
Contary to popular belief, you can gain MORE MUSCLE TISSUE while eating a lower calorie surplus from CLEAN FOOD, then you can gain from a higher calorie surplus from SHIT FOOD. So, don't convince yourself that you can eat whatever the fuck you want because it will build muscle, it WON'T! I can gain more muscle on 4,000 calories of quality amino acids, fats, and carbs, than I can from 8,000 calories of shit. A good example of this is how bodybuilders can GROW while dieting for a contest, due to the intake of extremely high quality calories.
As far as TRAINING, I believe that most bodybuilders are severely UNDER-TRAINING, but that's another issue entirely.