Protein for Healing

For many years, I subscribed to the popular belief that protein was something easily obtained from a "clean," plant-based diet.  Nuts and seeds, quinoa (!), or the ole rice and beans combo were the answers to all the body's needs.  I thought I was being the healthiest.  Animal protein wasn't exactly banned from my table, but it was mostly relegated to the dinner slot.  I had read that it was hard to digest.  My vegetarian friend told me it could turn rancid in the gut.  Neither of us knew what she was talking about but the implications were clear.