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,
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