Involuntary servitude means you have no choice, not that you aren't fed in the process. Indeed, even slaves are usually fed and housed since they constitute an investment on their owners' part (usually not well fed or housed, of course). The camps where you were forced to work without eating were known as death camps, which fortunately would fall under the cruel and unusual punishment clause here.
Note all that extreme overcrowding, a lack of nutritious food as well as a lack of heating and cooling were mentioned in the demands. If they are correct, it's hard to imagine worse conditions aside from outright torture.
They are incarcerated for a reason (yes there are cases of innocence - but realistically, the majority of offenders are in there for a reason). Whether it was a crime out of necessity, passion or simply because the perpetrator was downright crazy - they committed a crime, and their legal rights should be minimized to a minimum without making it a case of human rights violations.
If a work or education program can be offered to help people possibly correct their lives, excellent - if rehabilitation is possible - great. But they should not have the same rights as regular law abiding citizens.