Henry was a man of large appetites, in so many ways. Until he was in his late 30s, he was an Adonis and Olympic-level athlete, and he ate to match the calorific needs of his muscular, 6'2" body. Like many athletes, he continued to eat this way even when middle age slowed down his metabolism, meaning that while he still rode and jousted as much as ever, he was getting a bit thick in the middle. We've all, I believe, seen this happen to formerly strapping men. They call it the "dad jeans" phase in America; when men start wearing jeans a little bigger, a little looser, and with a little more room in the backside. They are by no means obese, but they are no longer the ab-showing gods of their youth.
That was the stage Henry was in when he had his terrible jousting accident in January of 1536. After the accident, he never jousted again. His legs had become too weak (either from the osteomyelitis-related ulcers or from McLeod's syndrome) to hold himself into the saddle when a lance struck him. However, he did still ride long hours almost every day in hunting, and while he remained an equestrian, his girth remained in check. Sadly for the king, the ulcers on his legs began to be too painful to ride or to even move around easily. In a relatively short time period Henry changed from a sportsman to a near-invalid.
Contrary to popular belief, it is not being fat per se that makes you ill; it is being sedentary that kills you. You can be up to 'morbidly' obese and in excellent health if you are getting regular exercise, even if it is mild to moderate exercise. In Henry's case, the more sedentary he became, the fatter AND sicker he got. A lack of exercise probably caused him to develop Type II diabetes and heart disease as well. As he gained excess fat and his muscles deteriorated from lack of use, it made it harder for him to move, which meant he got even LESS exercise, which in turn meant he got MORE ill and obese. It was a vicious cycle that killed him only 11 years after his last jousting accident.
For more details on his health, and explanations of the various maladies he may have had or probably didn't have, I summed them up in Henry VIII's Health in a Nutshell, which you might enjoy reading.
Kyra's books include Blood Will Tell: A medical explanation for the tyranny of Henry VIII, Henry VIII's Health in a Nutshell, Edward VI in a Nutshell, The Jezebel Effect: Why the slut shaming of famous queens still matters and the novel Mansfield Parsonage.