Perhaps the two most popular proteins on the market today are Casein and whey. They are both derived from milk, but they have very different attributes. In typical cow’s milk, 80% of the protein is casein protein and 20% of the milk protein is whey.  These proteins are considered complete proteins, meaning they contain all of the essential amino acids that you require from food and that you can not produce yourself.  The main difference between these two proteins is that casein protein is absorbed much slower into your body than whey. Casein is broken down for four to five hours in your body after it is consumed, while whey is broken down in only 90 minutes.  Casein is best to take before sleeping because, while you sleep, your body goes into a fasted state. Slow-release protein gives your body protein to absorb all through the night, providing you with a constant release of amino acids and protein synthesis throughout the night.  Whey protein, on the other hand, is perfect for a post-workout boost since it is absorbed quickly and will kickstart muscle recovery fast.