This purpose of this study is to perform a pilot investigation to determine if opioid peptides such as casomorphin can be detected in human plasma after cheese ingestion.

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.

Casomorphin receptor binding has been demonstrated in opiate receptor assays and bioassays. Duodenal aspirates from human volunteers given cow's milk have demonstrated the presence of several casomorphins, particularly β-casomorphin-7. Few studies have assessed the presence or action of casomorphins in humans. The ability of casein-derived opioid peptides to pass into the bloodstream is not well characterized, and is the subject of the present study.

Inclusion Criteria:

• Age greater than 18 years
• Male or female
• Either self-described as having a strong liking for cheese, or have been following a vegan diet for a least the previous six months.

Exclusion Criteria:

• Unstable medical status
• Physical condition affecting eating behavior, digestion, or intestinal absorption
• Dairy allergy or lactose intolerance
• Pregnancy
• History of severe mental illness
• Smoking during the past six months
• Alcohol consumption of more than two drinks per day
• History of substance abuse or dependency followed by any current use
• Inordinate fear of blood draws