Casein protein is a type of protein supplement that is derived from milk. It is a slow-digesting protein that is rich in essential amino acids, making it ideal for promoting muscle growth and recovery. Casein protein is often referred to as the “slow-release” protein, as it is slowly broken down by the body over a period of several hours, providing a sustained release of amino acids to the muscles. This makes it a popular choice for use as a nighttime protein supplement, as it can help to prevent muscle breakdown during periods of fasting such as sleep.