how do prisoners have so fit bodies if they don't eat enough protein?

hey, as the title says, how do prisoners who are eating crap, not getting enough protein manage to have so toned bodies?

Doesn't that mean that the protein that most people online recommend that you need to grow muscles is too much? I am not talking about body builders or professional athletes, but the rest of do we really need 1.6g per kg of protein, if not more that some suggest? Researches show different numbers. Some say 1g is enough others say 1.6g...how do you know what to follow?

Nevertheless, I have to say that I understand that every body has different needs and corresponds differently to these things. Also, age and sex plays a factor, but as a rule of thumb I think that there should be a rule.