Would the U.S.A. prison system benefit from a standard dog food like (for humans) food system?

I was wondering why cook meals and let people get fat in prison? I see on TV prison people eating better than me! Why not have very basic supplement, like dog food (for humans) that would supply the most basic nutrients? Maybe several varieties formulated for Diabetics, Aging, youth, special supplement.... I think it could save the Government Billions! Too, maybe people would not want to commit crime based on the basic sustenance they would be forced to eat?