General

I want to know if anyone has managed to go from a thin body to a very massive body +500lbs.
Because I have the impression that people weighing +500 lbs were all already fat, whereas people who gained by starting out slim can't get over 300 lbs.
I also have the impression that the thin people who win have visceral fat (balloons) and not soft subcutaneous fat.

I'll let you know when I get there

But for real, it's possible, not easy or likely, but possible over a long enough timeframe. Look at old pictures of the model LisaLou, she was a track runner or something like that, over the course of a decade she's gotten massive.