This is from the 3,000 calorie challenge thread, I finally explained this in a way that I was reasonably satisfied with, so I wanted to put it here, too.
How the whole “fat first, overeat later/ calories don’t count” thing works:
The body’s regulation of fat is messed up, so the concept of “excess calories” falls apart.
Lean Larry and Beefy Bob both need 1500 calories to get through the day.
Lean Larry eats 1500 calories. His body burns them all as fuel.
Beefy Bob eats 1500 calories. His body burns 750 and turns 750 into fat. Bob has so little available to run his system, he slows down to compensate. He also gets very hungry, because his body didn’t let him burn all 1500 of those calories, even though he really needs 1500 calories, it stored them as fat. Since he did need them, but his body misapplied them, his body tells him to go eat more.
His body created the fat inappropriately because his fat regulation mechanisms are not functioning properly, because his diet, combined with his genetics that predispose him to fat regulation breakdown under certain conditions, combine to break down that fat regulation system and essentially “break” his body’s normal ability to correctly deal with his food. So his body takes perfectly normal, healthy, appropriate calories and inappropriately turns them into fat. Then, because Bob is now fatter, having been robbed of the calories he needed to function by his body’s messed up decision to take half of them and stuff them in his fat cells, his body tells him to go get more calories.
So to the naked eye, it appears that Bob eats too much and therefore he’s fat. But in fact, Bob’s fat, so he eats more. (Not “too much” - he’s eating what his body is telling him to eat after his body decided to make half his calories into fat.)
Conventional wisdom dictates that it’s Beefy Bob’s tough luck and he evidently needs to confine himself to 750 calories a day in order to avoid gaining weight, and 500 if he wants to lose. Obviously, since bob is tired and hungry eating 1500 calories, eating 750 calories is going to put him into a coma and when he wakes up he’s going to want to eat everything in sight. But conventional wisdom says that’s what he should do, and if he doesn’t, it’s because he’s weak-willed and self-indulgent.
But Bob’s body, given only 750 calories, will burn 300 and store the other 450 as fat. then Bob will grow weaker, more lethargic, and insanely hungry. If Bob fails to eat more calories, Bob’s body is likely to start breaking down Bob’s muscles and non-fat tissue for fuel, because Bob’s regulatory system for all this is fucked up and his body wants him to have a certain amount of fat, and will make sure he does, no matter how much ***or how little ***Bob actually eats.
Which explains why Bob finds it so incredibly difficult to lose weight. His body doesn’t want him to and makes him very miserable to keep him from doing so.
All this is a result of a very high carbohydrate diet, likely very high in very simple carbs, which cause Bob’s pancreas to send tons of insulin into his body to deal with the carbs. Insulin is the body’s primary fat-regulation hormone and it is responsible for this mayhem. The goal is to dial down insulin’s mayhem. So Bob needs to dial down the carbs until he finds what level of carbohydrate he can safely eat without triggering this messed up fat regulation system to inappropriately store his food as fat instead of burning it off.
So, if Bob might be able to safely consume 50 grams of high-fiber carbohydrate without causing the insulin mayhem, he will be able to eat whatever protein and fat he likes, because his body’s fat regulation mechanism will work correctly, burning, storing, and excreting whatever it needs to to keep his system at optimal function, including his weight. If he usually needs 1500 calories and he eats 2000, his correctly functioning fat regulation system will recognize Bob has no need for 500 calories of bodyfat, so it will burn them off and excrete them rather than store them.
This same correctly-functioning system will recognize, once it is pulled out of it’s carbohydrate -induced haze, that Bob’s body already has way more fat than Bob actually needs, so, even though Bob is eating his normally required 1500 daily calories, it will kick into gear and start burning off that excess.
And that is how and why a carb-restricting diet that pays no attention to calories works.
Of course this is insanely simplified, but the best I can do. If you want to know more, read this book.