I watched that last night. I was flipping back and forth between that and Addicted to Food. I'm telling you, I'm addicted to those shows. Maybe b/c I can't imagine how one can let oneself go so so much to get to that point.
Did a quick search. "Joined For Life: Abby and Brittany Turn 16" will be repeated on The Learning Channel on Sunday evening, March 25.
Probably because he weighed 250 lbs as a kid. That means he probably dieted off and on most of his life. Each time he dieted, his metabolism slowed more and more. Pretty soon he was gaining weight on 1200 calories. After awhile, he probably just gave up, ate what he wanted and waited to die.