I was a bit surprised to learn that this corpulent king was actually quite dashingly good looking in his youth. However all images of him in public consciousness are always this obese guy. He was also quite the athlete from what I have gleaned from the histories. I know he must of liked to eat but is there anything, like a event or something that led to this change in attitude?
What happened?
Edit: clarification
While it's hard to point to a single factor determining anyone's weight, Henry VIII's bad legs were almost certainly a factor. He had some lower body injuries in his youth, but a major factor seems to have been a badly-healed injury from jousting accident in 1536. Problems related to the badly-healed injury nearly killed him, he developed ulcers on his legs that required painful treatment and limited his mobility at times.
There's been some theorizing about genetic diseases and attempts at coming up with a more concrete diagnosis, but I can't tell you how much of it's valid.