Applied Nutrition Micellar Casein protein, or what is also known as cheese, is found in cow’s milk, and casein protein in milk represents 80% of the total proteins in it, and this protein is also present in milk and is found in high-quality protein sources because it contains all the essential amino acids that the body needs from food because it cannot manufacture it on its own. In addition, casein is easier for the body to digest and absorb and helps muscle cells continue to synthesize protein while you sleep.