According to the Department of Anaesthesia and Intensive Care of the Chinese University of Hong Kong, a protein drink is digested in approximately two hours. According to Wikipedia, the digestion starts in the stomach and is completed by the time the food reaches the ileum.
After initial digestion, a protein shake leaves the stomach in approximately 30 minutes, according to The Department of Anaesthesia and Intensive Care of the Chinese University of Hong Kong. The Journal of the International Society of Sports Nutrition reports that viscous liquids such as protein shakes need 1.5 hours to pass the small intestine, where final stages of the digestion process are carried out.
