Cheese is one of the most commonly craved foods, suggesting the possibility of opiate activity, as has been demonstrated with other craved foods, particularly chocolate. Like other dairy products, cheese contains casein, which is the major protein in cow's milk. This is unlike human milk, in which the primary protein is whey. Casein includes αs1-, αs2-, β- , and κ-casein, with αs1 and β forms predominating. Human and bovine casein molecules are cleaved during digestion to release opioid peptides that are believed to have biological properties relevant to infant physiology and behavior. Specifically, β-casein is cleaved to form β-casomorphins. Like other opiate agonists, β-casomorphins prolong gastrointestinal transit time and have an antidiarrheal effect.