I didn't say it was trivial, just not a crazy amount! :-)
No doubt calories in/calories out must ultimately be obeyed, and you could w/ strictly controlled feeding achieve any weight you want by titrating calories, but I think people often misinterpret this fact to mean that any two isocaloric diets will result in the same weight; that's untrue because the "out" side of the equation is not constant -- different foods have different effects on your metabolism.
(And also appetite, which from a pratical perspective, is also hugely important -- most people don't rigerously eat X calories, they eat until they don't feel like eating anymore.)
No doubt calories in/calories out must ultimately be obeyed, and you could w/ strictly controlled feeding achieve any weight you want by titrating calories, but I think people often misinterpret this fact to mean that any two isocaloric diets will result in the same weight; that's untrue because the "out" side of the equation is not constant -- different foods have different effects on your metabolism.
(And also appetite, which from a pratical perspective, is also hugely important -- most people don't rigerously eat X calories, they eat until they don't feel like eating anymore.)