Well, here's what I know about jail. I know someone who spent time in Tent City (that crazy county jail in Phoenix.) She was on the female side. Anyway, she said when she was there she was the only one losing weight. There's a lot of people in there who are addicts and are skin and bones when they go in, their jail clothes just hang on them. But once they are there a while, the clothes start to fit and they start to get their color back. The food sucks and is disgusting, but it's still 3 square meals a day and no drugs, so these girls are getting cleaned up better than they do in their own lives, and many of them actually have appetites (which they don't when on the drugs.)
Of course, jail sucks. A lot of aggresion and so on. Fights over tiny little things. But, she has a lot of self-care issues. Like major ones. Weeks and weeks without showering or brushign her hair. Her hair turns into these huge mats. Well, when she was in there she went in with her hair hard as a rock stuck together. When she came out, it was beautifully brushed and braided. She said all her cell mates took turns working on her hair. So, evne though there is a lot of crap in jail, there was kindess, too.
So, her one time in jail was her last. Hopefully it will be that way for your son. Hopefully this will turn him around. Sometimes people need to lose everything before they see what they had. I know that sucks. I wish it wasn't that way.