exactly WHERE are you basing your observation? you spend a lot of time in prison visiting inmates, or are you thinking that Oz is realistic?
I can tell you're not a guard or you'd have seen the mess hall.
Surely you thought this out better. Prison food is crap. Bologna and white bread with generic chips is lunch...
However, if you work out for 3 hours a day, everyday, you're going to be huge. I would definately work out all the time, as to avoid the anal rapings.
I suggest you go to prison for 3-5 and try their workouts. Watch your ass though. You don't wanna get violated.. Or do you?