Other fascinating―and disturbing―findings have emerged.
Human milk contains casein, too, albeit less than in cow's milk and in a slightly different form.
In studies of women who had recently given birth, Swedish researchers found that opiates from breast milk sometimes pass from the breast into a woman's own bloodstream and then into the brain.
Some women with very high levels of these opiates in their blood― opiates that came originally from the casein in their own breast milk― have developed postpartum psychosis.
It had long been suspected that this syndrome of confusion, hallucinations, and delusions (symptoms that go beyond the mood changes of postpartum depression, a more common disorder) is not simply due to the stresses of childbirth, the arrival of maternal responsibilities, or the loss of youthful innocence.
The fact is, something is poisoning the brain.
The Swedish researchers suggested that that “something” might be an opiate released from casein in mother's milk.
The point is, casein is as much a drug as a nutrient, and it is a primary ingredient in all milk products, but especially in cheese.
Cheese contains far more casein than is found in milk from either cows or humans.
And it holds other druglike compounds as well.
It contains an amphetamine-like chemical PEA, phenylethylamine, that we looked at earlier, which is also found in chocolate and sausage.
And there are many hormones and other compounds in cheese and other dairy products whose functions are not yet understood.
Researchers are gradually tearing them apart and trying to understand their biological effects, including their contribution to the cheese craving that is so common.