this is a subject that is very close to me, in ways i guess i'm not really ready to reveal as yet.
What you are really asking is "what is the cause of morbid obesity?" All of the reading i have done indicates that it is a complex disease, with genetic, behavioral and environmental factors. It can't be attributed to just one cause. There are many many as yet unexplained biological factors that impact overeating: leptin, the stomach hormone grehlin, brain chemicals, genetic predisposition.
I have seen the show you talked about, and remeber, the man was already suffering from moribid obesity BEFORE he met and married the woman. I don't doubt she also played a part, as many in the show seemed to notice.
Morbid obesity is a terrible disease, and the sufferers often are regarded in the same way as those of us with depression: just get over it: just stop eating: etc etc.

I have watched several of those shows profiling people with morbid obesity and just like us, each one is an individual with a painful disease, you can just see theirs on the outside.

Boo Radley