When I moved out of an 8-year stint of vegetarianism years ago (into a simple what-I-was-used-to-eating-just-now-with-meat, I hadn't heard of Primal yet), I had some stomach issues that did go away on their own. A holistic herbally lady friend said it was low stomach acid, so I introduced the meat a bit slower and issues cleared.
By the way, the advice on the Swedish bitters is very good, too, just in case you have never heard of them. My whole extended family uses them as needed for such issues. The family probably would get rid of the issues all together if they rejiggered their diets, but hey, everybody makes their own decisions.
I have a mantra that I have spouted for years... "If I eat right, I feel right. If I feel right, I exercise right. If I exercise right, I think right. If I think right, I eat right..." Phil-SC