R1 Casein is a slower digesting protein compared to whey protein. As a slower digesting protein R1 Casein works well between meals and at bedtime when more sustained amino acid delivery is desired. The most important muscle building and regeneration processes occur at night while you're sleeping. Therefore, it is necessary to provide your muscles with the nutrients that are needed for these processes. Casein is a slow-digesting protein that breaks down more slowly, delivering its amino acids over several hours.