That's not what the OP is suggesting, though. "calories in, calories out" does not mean that my 2,000 calories is the same as someone else's 2,000 calories. It

That's not what the OP is suggesting, though. "calories in, calories out" does not mean that my 2,000 calories is the same as someone else's 2,000 calories. It means that if I am gaining weight eating 2,000 calories a day, I will eventually lose weight if I eat fewer and few calories. (ie, I may not lose weight at 1,900 calories per day, but I would absolutely lose weight at 500 calories per day.)