Thanks to high school Biology, we all understand how important proteins are. in fact, we have been told about proteins right since primary school days in elementary science. In case you are a little rusty on that bit of knowledge, allow me quickly remind you in one short sentence: Protein is an essential nutrient, responsible for multiple functions in your body, including building tissue, cells and muscle. Imagine the picture of a child with kwarshiorkor - that helps reinforce just how bad protein deficiency can be. There are very many sources of protein, but some of the best and most readily and affordably available are mentioned below.