This was on tonight & it made me think/question if there ever was a story written with a similar scenario but where a thin/fit women body swapped with an chubby over-eater & over time physically transformed the present body to resemble the personality of the host. (i.e fit body gained weight & fat body became fit). It seems to me that there was something like this written but I'm not finding it, perhaps I'm wrong, if so it sounds like a good premise, "hint".