The Magic Of Breasts

The Guardian:

Scientists used to think breast milk was sterile, like urine. But it's more like cultured yoghurt, with lots of live bacteria doing who knows what. These organisms evolved for a reason, and somehow they're helping us out. One leading theory is they act as a vaccine, inoculating the infant gut. A milk sample has anywhere from one to 600 species of bacteria. Most are new to science.
Then there are the sugars. There's a class of them called oligosaccharides, which are long chains of complex sugars. Scientists have identified 140 of them so far, and estimate there are about 200. The human body is full of oligosaccharides, which ride on our cells attached to proteins and lipids. But a mother's mammary gland cooks up a unique batch of "free" or unattached ones and deposits them in milk. These are found nowhere else in nature, and not every mother produces the same ones, since they vary by blood type. Even though they're sugars, the oligosaccharides are, weirdly, not digestible by infants. Yet they are a main ingredient, present in milk in the same percentage as the proteins, and in higher amounts than the fats. So what are they doing there?
They don't feed us, but they do feed many types of beneficial bacteria that make a home in our guts and help us fight infections. In addition to recruiting the good bugs, these sugars prevent the bad bugs from hanging around. "The benefits of human milk are still underestimated," said Lars Bode, an immunobiologist at the University of California, San Diego. "We're still discovering functional components of breast milk."

There's also a whole lot about how the environment affects what ends up in the milk.  Prior to scrapping the EPA, Republicans may want to read the article.