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30% материнского молока предназначается именно им
Как известно, этот блог обходил стороной сиськи, хохлосрач и котиков отчего и платился популярностью. Но к чему эта преемственность?  Тем более, когда речь "почти" напрямую заходит о прекрасной части женского тела. Да и вечер уже. Цитирую суперкнигу I Contain Multitudes о микробах. 30% материнского молока предназначается именно им.

“Mother’s milk is full of antibodies which control the microbial populations of adults – and babies take up these antibodies during breastfeeding. When immunologist Charlotte Kaetzel engineered mutant mice that could not produce one of these antibodies in their milk, she found that their pups grew up with bizarre gut microbes. They were full of species that are typically found in people with inflammatory bowel diseases, and many of these bacteria wormed their way through the gut walls to inflame the lymph nodes lying underneath. As we saw earlier, many harmless bacteria are harmless only by virtue of where they are. Milk keeps them restrained. And it does much more than that. Milk is one of the most astounding ways in which mammals control their microbes.

 Milk is a mammalian innovation. Every mammal mother, whether platypus or pangolin, human or hippo, feeds her baby by literally dissolving her own body to make a white fluid that she secretes through her nipples. The ingredients of that fluid have been tweaked and perfected through 200 million years of evolution to provide all the nutrition that infants need. Those ingredients include complex sugars called oligosaccharides. Every mammal makes them but human mothers, for some reason, churn out an exceptional variety – scientists have identified over 200 human milk oligosaccharides, or HMOs, so far. They are the third-biggest part of human milk, after lactose and fats, and they should be a rich source of energy for growing babies. But babies cannot digest them.

When German first learned about HMOs, he was gobsmacked. Why would a mother spend so much energy manufacturing these complicated chemicals if they were indigestible and therefore useless to her child? Why hasn’t natural selection put its foot down on such a wasteful practice? Here’s a clue: these sugars pass through the stomach and the small intestine unharmed, and land in the large intestine where most of our bacteria live. So, what if they aren’t food for babies at all? What if they are food for microbes?

This idea dates back to the early twentieth century, when two very different groups of scientists made discoveries that, unbeknownst to them, were closely connected. In one camp, paediatricians found that microbes called Bifidobacteria (or Bifs to their friends) were more common in the stools of breast-fed infants than bottle-fed ones. They argued that human milk must contain some substance that nourishes these bacteria – something that later scientists would call the ‘bifidus factor’. Meanwhile, chemists had discovered that human milk contains carbohydrates that cow milk does not, and were gradually whittling this enigmatic mixture down to its individual components – including several oligosaccharides.

These parallel tracks met in 1954, thanks to a partnership between Richard Kuhn (chemist, Austrian, Nobel laureate) and Paul Gyorgy (paediatrician, Hungarian-born American, breast-milk advocate). Together, they identified all the HMOs, pulled them out of milk, and fed them to bacteria. And, to their chagrin, nothing grew. The problem soon became clear: HMOs are not an all-purpose food for Bifs. In 2006, the team found that the sugars selectively nourish one particular subspecies called Bifidobacterium longum infantis, or B. infantis for short. As long as you provide it with HMOs, it will outcompete any other gut bacterium. A closely related subspecies – B. longum longum – grows weakly on the same sugars. The ironically named B. lactis, a common fixture of probiotic yoghurts, doesn’t grow at all. Another probiotic mainstay, B. bifidum, does slightly better but is a fussy, messy eater. It breaks down a few HMOs and takes in the pieces it likes.

By contrast, B. infantis devours every last crumb with a cluster of 30 genes – a comprehensive cutlery set for eating HMOs. No other Bif has this genetic cluster; it is unique to B. infantis. Human milk has evolved to nourish this microbe and it, in turn, has evolved into a consummate HMOvore. Unsurprisingly, it is often the dominant microbe in the guts of breast-fed infants. It earns its keep. As it digests HMOs, B. infantis releases short-chain fatty acids (SCFAs) that feed an infant’s gut cells – so while mothers nourish this microbe, the microbe in turn nourishes the baby. Through direct contact, B. infantis also encourages gut cells to make adhesive proteins that seal the gaps between them, and anti-inflammatory molecules that calibrate the immune system. These changes only happen when B. infantis grows on HMOs; if it gets lactose instead, it survives but doesn’t engage in any repartee with the baby’s cells. It unlocks its full beneficial potential only when it feeds on breast milk. Likewise, for a child to reap the full benefits that milk can provide, B. infantis must be present. For that reason, David Mills, a microbiologist who works with German, actually sees B. infantis as part of milk, albeit a part that is not made…

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