Actually prisoners are studied quite a bit. It’s an interesting question!
I emailed some professors out of curiosity. Here’s one study that’s interesting. They also apparently use unappealing food (all high carb of course) that is nutrient dense but tastes unappealing as punishment. At any rate, according to this one, it states that women typically gain more weight than men.
I do know it’s an issue (at least in Statesville here) that food costs are cut and cheaper things are utilized more frequently at the expense of prisoner health.