Casein is the predominant protein in milk. For example, the protein in cheese and cottage cheese is casein. Sometimes it's shown on the label as caseinate or micellar casein. Milk (casein) is a slow digesting protein that provides a steady stream of amino acids to your muscles -- up to 7 hours. It also has a naturally high glutamine content, higher than whey, egg or soy. Because of its prolonged release effect, it's one of the best proteins for preventing muscle breakdown and is very low in lactose.
Protein powders with casein are excellent for meal replacements for a breakfast shake or when you want a shake to really fill you up. A milk protein-based shake is commonly taken right before bed to keep your muscles fueled with protein throughout the night.