If you were to look at a protein molecule with a powerful microscope, it would look like a long string of beads. Each “bead” is a protein building block called an amino acid, and, during digestion, the individual amino acids come apart and are absorbed into your bloodstream so that your body can use them to build proteins of its own.

So the calf digests the proteins in milk, breaking apart the chain of beads and using these amino acids to build skin cells, muscle cells, organs, and the other parts of the body.

However, casein is an unusual protein. While it does break apart to release individual beads, it also releases longer fragments—chains that might be four, five, or seven amino acid beads in length. These casein fragments are called casomorphins—that is, casein-derived morphine-like compounds. And they can attach to the same brain receptors that heroin and other narcotics attach to.

In other words, dairy protein has opiate molecules built right into it.

Opiates in dairy products? What the heck are they doing there, you might ask. Well, imagine if a calf did not want to nurse. Or if a human baby was not interested in nursing. They would not do very well. So, along with protein, fat, sugar, and a sprinkling of hormones, milk contains opiates that reward the baby for nursing.

Have you ever looked at a nursing baby’s face? The infant has a look of great intensity and then collapses into sleep. Of course, we imagine that to be the beauty of the mother-infant bond. But the fact is, mother’s milk delivers a mild drug to the child, albeit in a benign and loving way. If that sounds coldly biological, it pays to remember that nature never leaves anything as important as a baby’s survival to chance.

Opiates have a calming effect, and they also cause the brain to release dopamine, leading to a sense of reward and pleasure.

A cup of milk contains about 7.7 grams of protein, 80 percent of which is casein, more or less. Turning it into Cheddar cheese multiplies the protein content seven-fold, to 56 grams. It is the most concentrated form of casein in any food in the grocery store.

Call it dairy crack. Just as cocaine manufacturers have found ways to turn an addictive drug (cocaine) into an extremely addictive one (crack), dairy producers have found their own ways to keep you coming back. In the Middle Ages, cheese makers had no idea that cheese might concentrate milk’s addictive qualities. But today’s cheese industry knows all about cheese craving and is eager to exploit it. It is doing its level best to trigger cheese craving in vulnerable people.