Like whey protein, casein is a complete protein containing all of the Essential Amino Acids. Also like whey, casein is made from cow’s milk. One major difference is casein’s rate of digestion, which is much slower than whey. This is why many active adults consume a casein protein shake before bed. A study published in the Journal of the International Society of Sports Nutrition suggests timing might not be as important as hitting a daily protein target.

Thirteen male subjects participated in a 10-week training program. All received 1.8 grams of protein per kilogram of body weight through foods. They also consumed 35 grams of casein protein per day. Some subjects drank their casein shakes at night while others consumed them during the day.

Compared to measurements taken before the program began, subjects gained an average of 2.8 kg of muscle mass with daytime casein and 2 kg with nighttime casein. Leg press strength increased 80.1 kg with daytime casein and 83.9 kg with nighttime casein. Bench press strength increased 12 kg for the daytime group and 8.3 kg for the nighttime group. These were not considered statistically significant differences.