hehe, I have high tolerance I'll give some details. Basically your body is the ultimate constantly evolving machine. It 'evolves' or adapts to physical stress very well. Frequen heavy lifting is a big physical stress. In order to 'evolve' your body wants to put on more muscle so that it can handle the same stress adequately next time it faces it. If you are eating a certain amount and not really gaining or losing weight while not lifting, obviously you are gonna need to eat more to add this muscle, that entire e=mc^2 thing...matter doesn't get created or destroyed, only changed forms, and that equation there also account for energy/mass which is why you need more calories than just for adding more weight...energy!, kinda neat that theory of relativity can be (loosely) applied to body building
Anyway, if you constantly have the calories coming your body will be much more willing and able to adapt to the stress of heavy exercise. And, most importantly, it doesn't really do this adapting while your lifting. It does it while you are resting and on your days off. So if you're only eating big on lifting days you aren't giving your body the fuel it needs on rest days to add the mass. Also, eating high calories every day will let your body know its ok to add muscle because the building blocks and the fuel are gonna be there...its like would you try and rebuild a car if you could only get spark plugs once a year and gas only once every month? No, it owuld be pointless and a waste of your time. Thats why consistancy is important... I'm sure others have other opinions but I think thats the gist of it. Search more if you want other opinions...just keep in mind they will be wrong and that mine is the only correct one!
J
