500 is pretty normal on MPA, and does stop working for most people eventually, even if they're a really high bmi. A lot of non-anorexic overweight people do underestimate their calories, but I remember when I was on 500 cal/day, counting and weighing everything, and stopped losing weight after about 25lbs. I was 70lbs, but I'm guessing it's a similar biologic response whether you're underweight or overweight. The body doesn't want to die. (Lol sorry I doubt anyone cares but I just wanted to say that)