The point is that the reason that there's so much diet advice out there beyond calories in < calories out is that accomplishing calories in < calories out on an ongoing basis is HARD.
The advice (aside from the scams and a little bit of idiocy) is on how to achieve that deficit in a way that minimizes the willpower required - because humans suck at willpower and one's biology is constantly trying to undermine that willpower in order to achieve the "store more reserves" imperative.
The advice (aside from the scams and a little bit of idiocy) is on how to achieve that deficit in a way that minimizes the willpower required - because humans suck at willpower and one's biology is constantly trying to undermine that willpower in order to achieve the "store more reserves" imperative.