[National Geographic blog post] Could mothers’ milk nourish mind-manipulating microbes?
From the 8 April 2015 post
Breast milk seems like a simple nutritious cocktail for feeding babies, but it is so much more than that. It also contains nutrients that feed the beneficial bacteria in a baby’s gut, and it contains substances that can change a baby’s behaviour. So, when a mother breastfeeds her child, she isn’t just feeding it. She is also building a world inside it and simultaneously manipulating it.
To Katie Hinde, an evolutionary biologist at Harvard University who specialises in milk, these acts are all connected. She suspects that substances in milk, by shaping the community of microbes in a baby’s gut, can affect its behaviour in ways that ultimately benefit the mother.
It’s a thought-provoking and thus far untested hypothesis, but it’s not far-fetched. Together with graduate student Cary Allen-Blevins and David Sela, a food scientist at the University of Massachussetts, Hinde has laid out her ideas in a paper that fuses neuroscience, evolutionary biology, and microbiology.
It begins by talking about the many ingredients in breast milk, including complex sugars called oligosaccharides. All mammals make them but humans have an exceptional variety. More than 200 HMOs (human milk oligosaccharides) have been identified, and they are the third most common part of human milk after lactose and fat.
Babies can’t digest them. Instead, the HMOs are food for bacteria, particularly the Bifidobacteria and Bacteroides groups. One strain in particular—Bifidobacterium longum infantis—can outcompete the others because it wields a unique genetic cutlery set that allows it to digest HMOs with incredible efficiency.
Why would mothers bother producing these sugars? Making milk is a costly process—mums quite literally liquefy their own bodies to churn out this fluid. Obviously, it feeds a growing infant, but why not spend all of one’s energy on filling milk with baby-friendly nutrients? Why feed the microbes too? “To me, it seems incredibly evident that when mums are feeding the microbes, they are investing on a greater return on their energetic investment,” says Hinde. By that, she means that setting up the right communities of microbes provides benefits for the baby above and beyond simple nutrition.
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