I was surprised to read in The New York Times Science section this week that a full twenty one percent of breast milk is indigestible—human babies can’t break it down and therefore don’t use it for nutrition.
The article—a review of research being conducted by a group at the University of California, Davis—points out that the milk-mom-baby system has had 200 million years of mammalian evolution to perfect itself, so scientists have always wondered what purpose nature had for the extra ingredients.
The answer seems to be that the complex sugars in question (derived from lactose, the main carbohydrate in milk) don’t feed the baby, they feed a strain of bacteria called Bifidobacterium longum. Why would this be important?It turns out that these Bifido microbes coat the lining of an infant’s digestive tract and ward off toxic bacteria that would potentially make the baby sick. In the meantime, unwanted bacteria also bind to the complex sugars (the indigestible ones that were previously a mystery) and get flushed out of the baby’s system.
So it’s an intricate system of sugars and bacteria—and the amazing part to me is that until recently, we thought that what constitutes almost a quarter of breast milk didn’t serve any purpose at all. It makes you wonder what other secret components of breast milk are out there, doing an important job that we don’t even know about.