Casein protein is the predominant protein found in milk. It makes up about 80% of the protein in cow's milk, while the remaining 20% of protein in milk is whey. Casein protein is extracted from the milk through ultra filtration, without the use of chemicals. This process increases the amount of bioactive milk peptides that support immune function as well as enhance muscle growth. Casein protein has an excellent amino acid profile and is primarily known as an extremely slow-digesting protein.
Casein protein is a slow-digesting protein because it forms a "gel" in the gut, which results in a steady release of amino acids into the blood stream over time. Research shows that when you consume casein, you will reach a peak in blood amino acids and protein synthesis between three to four hours. The total release of amino acids in the bloodstream, however, can last as long as 7 hours after ingestion of casein protein! Whey protein, in comparison, reaches a peak in blood amino acids and protein synthesis in about forty minutes and the total release ends in about an hour.
Since casein protein slowly enters the blood stream, it has very little impact on protein synthesis. It has a powerful effect, however, in suppressing protein breakdown. In other words, it's an awesome muscle-sparing protein. Muscle growth is dependent on the balance of protein synthesis and protein breakdown. To tip the balance in your favor, you want to increase protein synthesis and decrease protein breakdown. You can achieve this by supplementing with whey protein (fast absorption/promotes protein synthesis) and casein protein (slow absorption/suppresses protein breakdown).
To effectively take advantage of whey and casein proteins, you need to use them at the right times of the day. Casein protein is the only protein you should be taking before going to sleep. The reason is because your body needs to be sustained for six to eight hours during your sleep without food. You don't want your hard-earned muscle being broken down in your sleep, so a protein that is slowly released over time is best.