This says it pretty straight forward 
Taken from sherdog.netMetabolic function for dummies (why the numbers aren't ALL there is to it)."Okay, so this thread is born out of the routine posting up here of "calories in vs calories out is THE important thing when considering weight gain/loss." I've long said it isn't, it's AN important thing, but there is no THE important thing because of some variables that occur in the human body that thwart this idea. So here I'm going to spell it out once and for all, that you don't just "eat more" to gain LEAN MUSCLE MASS. The holes in this theory are as follows, wether anyone likes it or not:
1) The body adapts to caloric intake being raised or lowered. Let's say for instance you're in a cutting phase. So you lower your caloric intake to tentatively burn stored bodyfat. As a shock to your system this will straight-away work quickly. However, you will inevitably plateau. This is because your body will systematically adjust to raised and lowered caloric intake by either burning or storing lesser or more calories. This is why everyone, when cutting or bulking, hits plateaus.
2) Some calories are more readily stored as BODY FAT. Yes, it's true. There is a reason for this, though. Out of carbohydrates, protein, and dietary fat, the fat is the most fattening (fat fattening...who'da thunk it!?). The reason is because as the body digests these macronutrients it requires the burning of calories to do so. Digesting fat requires the FEWEST amount of calores burned to digest (2-3 times less than carbs, 10 times less than protein). Thus, dietary fat yields the greatest net caloric intake for BODYFAT STORAGE.
3) Your hormones shift as you shift your caloric intake drastically. The most pertinent factor here is that high protein yields high IGF (Insulin Growth Factors) in the body, regardless of overall caloric intake. So it's important that a good bulk of (most of) your net caloric intake come from lean protein sources, not just any old food you can find that has high calories.
4) Glycemic Index impacts fat storage. The American Journal of Clinical Nutrition concluded that low GI eating supports processing of bodyfat even with high calories. Carbs that convert slower to glucose are more benefitial because they hinder bodyfat storage by affecting insulin secretion (meaning they do not cause insulin spikes). High GI foods used as a dietary staple for gaining mass will lead to greater bodyfat storage as insulin levels are spiked, high insulin levels make the body EXTREMELY efficient at storing fat.
5) Meal Frequency affects your metabolism. This is why how many meals per day you eat is important. You would be better served with 7 meals per day as opposed to 4 or 5. Why? Because every time you eat your metabolism increases a little and cortisol is suppressed. I don't think I need to further elaborate on that.
6) Time of day affects your metabolism. Oh no, here comes the voodoo about eating o'clock. It's long been known that insulin sensitivity is greater later on in the day, thus higher calories from any old source later in the day means insulin spiking, which means greater fat storage and possibly, diabetes.
Summation: - The numbers are also a factor, but they are far from the ONLY factor. They are a good bottom-line to go by, but not a nutritional guideline. Anyone who tells you otherwise and says "oh it doesn't matter what you eat as long as you have good protein and a lot of calories" without giving you the above information is tentatively steering you towards not only becoming FATTER, but also possibly having cholesterol problems, being diabetic, and having blood-pressure problems, all of which are more-times-than-not the result of terrible eating habits. And no, I repeat, NO...training alone will not alleviate these problems. In fact they may only serve to further complicate them. Now, leave us consider one thing now that many of you young impressionable people have read this. THIS IS NOT TO BE TAKEN AS GOSPEL. Why? It all kind of sounds okay doesn't it? Sure. Common sense will serve you well (on the flipside, lack of common sense will not avail your nutritional goals no matter how dilligently you stick to a single school of thought) here, but there is one variable NONE OF US can evade.
EVERYONE'S PHYSIOLOGY IS SLIGHTLY DIFFERENT. This means that some of these things apply moreso to some of you than they do to others. As well as some of you may not even BE affected by some of these things and others very health may depend on them. So regardless of information, YOU have to take your Health as YOUR OWN responsibility. Much the same as you do your intelligence. Meaning, before any of you dolts asks me to cite sources and shit think about this:
No. I'm not going to debate with you. Make your own decision wether you believe it or not. I will not do your thinking for you in terms of your own body. Furthermore, I will not attempt to stand on the shoulders of people who have done extensive studies and research and profess to know for FACT things I have only seen on a document. There is no need to attempt to substitute someone else's intelligence for your own. There is a subtle difference between relaying information, and representing onesself as a false prophet, if you get my meaning. Someone tells you something, if it smells like bullshit then chances are it is. If it sounds reasonable chances are it MIGHT be true enough to apply to you. And I'll tell you what sounds like bullshit to me.
Simply "eating more" to gain LEAN MUSCLE MASS. If this were true overeaters would be the most muscular people around with some exercise. I have an Uncle who is a trucker, and unloads and loads shit from his trucks on a daily basis, which equates to as strenuous a workout as most weight regimens. And he's FAT. How? He eats like shit, end of story. Plus, if this were true there would be NO SUCH THING as hardgainers. Almost every twig I've ever met looking to put on weight eats like a fucking horse as it is. Why then are they still skinny? See above. The foods they eat do NOTHING to combat their metabolic processes that keep them from storing MUSCLE.
You do NOT have to risk health complications to gain weight. There is a reason most bodybuilders, ESPECIALLY those over 250lbs eat "healthy" (despite occasional cheating) and stay relatively the same weight. There is also a reason bodybuilders (and any athlete for that matter) who do not abide by sensible eating habits look and are fatter during their off-seasons when they gourge themselves with un-healthy food. This isn't fucking brain surgery people."
