bulksupplements Casein Protein Powder - Low Carb Protein Powder What Is Casein Protein Powder? Casein protein powder is a protein derived from milk. Milk contains two types of protein: casein and whey. Whey protein is fast digesting, which means it is absorbed extremely quickly and is great for taking immediately after exercise. Casein protein is slow-digesting, which means it releases amino acids slowly instead of quickly like whey. Casein protein is often taken before periods of rest and sleep. Casein Protein Powder Benefits* Casein protein powder contains BCAAs and may assist in the recovery of muscles after strenuous physical activity. Supplementation of casein protein may also help with general development of lean muscle mass at a faster rate.