You cannot force people to be healthy. The kind of person you find in prison is not the kind of people who would be healthy inside or outside of prison walls. They are irresponsibile about everything and hardly models of hygene.
Joke: "What has four arms, four legs and four teeth?" Answer: "Two San Quinton inmates."
(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie.Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")