Ed Yong in The New Yorker:
The Foods for Health Institute, at the University of California, Davis, has the appearance of a Tuscan villa, its terra-cotta-walled buildings overlooking a large vineyard and a garden that bursts with summer vegetables. It is led by a chemist named Bruce German, and if there were a world title in extolling the virtues of milk he would surely hold it. At our first meeting, he spent half an hour monologuing on the subject, bouncing on an exercise ball and kneading a tattered shred of bubble wrap as he spoke. Milk, he said, is a perfect source of nutrition, a superfood that is actually worthy of the label. This isn’t a common view. The number of scientific publications about milk is tiny, compared with the number devoted to other bodily fluids—blood, saliva, even urine. The dairy industry has spent a fortune on extracting more and more milk from cows, but very little on understanding just what this white liquid is or how it works. Medical-funding agencies have generally dismissed it as irrelevant, German said, because “it doesn’t have anything to do with the diseases of middle-aged white men.” And nutritionists have looked at it as a simple cocktail of fats and sugars, one that can be easily duplicated and replaced by formulas. “People said it’s just a bag of chemicals,” German told me. “It’s anything but that.”
Milk is a mammalian innovation, common to platypuses and pangolins, humans and hippos, its ingredients varying according to what each species needs. Human milk is a particular marvel. Every mammal mother produces complex sugars called oligosaccharides, but human mothers, for some reason, churn out an exceptional variety: so far, scientists have identified more than two hundred human milk oligosaccharides, or H.M.O.s. They are the third-most plentiful ingredient in human milk, after lactose and fats, and their structure ought to make them a rich source of energy for growing babies—but babies cannot digest them. When German first learned this, he was gobsmacked. Why would a mother expend so much energy manufacturing these complicated chemicals if they were apparently useless to her child?