I also don't gain weight. I'm 22 male and I've been skinny since the third grade and have never been able to havea normal looking body. I think it's much more painful and bizarre not gaining weight, than for people who do! And the funny thing is, my entire life I've always eaten more in food in quantity than anybody around me. Since going paleo, my body size has actually felt and looked more rounded and even and bit more muscular. I've also lost some height which is good because I'm too tall for how skinny I am. Haven't lost any weight to be concerned about though, but havn't put any on. I'm currently experimenting with starchy vegetables because it's my guess that keeping our overactive insulin production high by keeping loads of carbohydrates is hyper metabolizing our entire system. I'm hoping a very low carb diet will make me feel better.