Sheldon had MS. He blogged about it inconspicuously on his site in a small Health section. As I recall it messed with his balance and he could no longer ride a bike, so he was riding around on a tadpole recumbent trike (thus satisfying Bikesnob's most stringent "Would you still ride if... " question).

on his site, he says that he used to weigh 270 lbs, and lost 50lbs with Atkins. i'm sure he gained plenty back when MS took his ability to ride a two-wheel bike (and probably many other physical activities) away from him. anyway, physical fitness doesn't necessarily prevent heart disease.