Slow digesting, by definition, means that the body is unable to process a food or supplement quickly. For instance, the body’s ability to process a soluble protein like whey is significantly faster than an insoluble protein like casein. Casein forms micelles — basically, clumps or clusters — layers of which are slowly peeled off during digestion. It can take up to seven hours to completely digest certain casein proteins, such as micellar casein, allowing the body to gradually utilize its properties.
Sometimes, a quick-digesting protein, such as whey, may pass too rapidly through the digestive system and into the intestines for the body to properly take advantage of all of the nutrients. Taking casein right before bedtime is ideal, as it provides a slow release of aminoacids, helping to prevent muscle breakdown and thus keeping your system more anticatabolic.