I like where you are going but let me throw this out there.  In Barbie World you can pig out and stay thin because genitikis and you don't have to work out for a six pack because what ever fattie excuse basically it's the world pigs believe is real.  Now she hits the real world and continues to eat like that and we keep Amy but her role is as a stunt double for what happens when you eat too much and let yourself go.  For the rest of the movie its about Barbie learning real self care like eating a human amount of food and working out and turning her from a beast to a person with both inner and outer beauty.  While in her journey she can meet inspirational people that are doing their best like a girl who is still killing it in the gym despite losing her legs in an accident.  Or a poor girl that is doing her best to put together a balanced meal with cheap pantry staples like beans and rice.