Casein is a protein that is found in milk and used independently in many foods as a binding agent. Technically, it is part of a group called phosphoproteins, collections of proteins bound to something containing phosphoric acid.It may also be called caseinogen, particularly in European foods.) Casein is a slow acting protein (opposite of whey) that is ideal for taking right before sleep if you are in the bodybuilding game. 6) Saying something causes cancer blindly and something does not is total ignorance because each individual reacts differently.