Can't we just use literal prisoners?

That's what I always thought about the kind of research RFK Jr is always talking about. Normally it's not ethical to do food / medicine trials with prisoners, but these would be trials like giving regular food to one set of prisoners and food without dyes or chemicals to the other. The "test group" would just be getting healthier food.

Seems like just radically measuring portion sizes might fit into the same kind of thing. And you could probably measure activity level more easily, too.