As I said in my original comment, this might seem obvious to you but unfortunately it’s not obvious to everyone. In addition, it’s also not necessarily correct: you can get fatter because you expend less energy too. I think empirically it seems like just looking at calorie intake and assuming the energy expenditures are fairly flat is a decent story but that’s definitely not a conclusion you can reach a priori.
As I said in my original comment, this might seem obvious to you but unfortunately it’s not obvious to everyone. In addition, it’s also not necessarily correct: you can get fatter because you expend less energy too. I think empirically it seems like just looking at calorie intake and assuming the energy expenditures are fairly flat is a decent story but that’s definitely not a conclusion you can reach a priori.