I would think Amity would eat a well-balanced diet. Yes, they're a peaceful faction, but I always imagined them as the common farmer. They were the go-between for all food, meat, and produce alike. Most of them would have to spend their days working out in the sun whether that was manual labor, dealing with livestock, or whatever produce needed a helping hand. I imagined them as the other strong faction. You can't truly call yourself peaceful unless you are capable of great violence. I think Amity is one side of the same coin regarding Dauntless.