Maybe, though I suspect there are probably a lot of laws around what you can and cannot do so better get several good lawyers to check what the laws really are around this. Drug treatment programs often work like this so that is the first place to look for laws to watch out for.

I've heard of other attempts at things like this. Generally you are not locked into a cell, you are removed to a very remote location by bus so that if you want to leave you have to go through a formal withdrawal process - while waiting for the bus - during which they convince you to stay). They then not only control your diet they also give you exercise (often lead by military drill instructors) thus being a healthier environment than a diet cell. I have no idea how much money they make.