What to Eat When Building Muscle? Our body begins to think we are being “starved” of protein, so in a self-defence mode it tries to keep protein in us, hence why when we damage the muscles, our body panics and begins forcing protein in there which is excellent. Muscle building nutrition is essential.We all know the basic foods we should be eating but we forget about some of the little tricks out there.We all know we should be eating things like chicken breasts, Full steaks, plenty of fatty fish like trout, rainbow trout, salmon, sardines, tilapia, full eggs, whey protein, casein protein.