Can someone get fat on a primal/paleo diet? Yes. Constant excessive calories will eventually get packed on as pounds. Paleo/primal is not like a safe "eat all you want" buffet (although a paleo buffet would have its attractions.) Ask this question: Were there any obese groks? Perhaps there was a rare exception but it is difficult to imagine any pre-agricultural revolution human being obese. They didn't have excess food enough to have obesity. Indeed women had to evolve into fat storers to have enough energy to be pregnant et cetera. All of this is to say the point of primal/paleo is not to eat all you want. It is to eat what is best for the health of the body. Eating all you can eat is not necessarily good even when primal/paleo.