A new study, the subject of a story by Nicholas Wade in The New York Times this week, reveals a little more of the magic of breast milk. It turns out that complex sugars in human milk encourage the growth of "good" bacteria that form a lining in a baby's gut, protecting her from dangerous microbes.

The baby can't digest the complex sugar, but the bifido bacteria can. In an article in the Proceedings of the National Academy of Sciences, Bruce German, Carlito Lebrilla and David Mills and colleagues describe the "intriguing strategy" lactation represents — to nourish microbes that can in turn protect a baby who has not yet developed an immune system of his own.

Dr. German told Wade, "We were astonished that milk had so much material that the infant couldn’t digest. Finding that it selectively stimulates the growth of specific bacteria, which are in turn protective of the infant, let us see the genius of the strategy — mothers are recruiting another life-form to baby-sit their baby."

The researchers used mass-spectometry-based tools to examine the structures of the complex sugars in breast milk. Their findings made the researchers think that milk holds even more secrets, even perhaps some that could help struggling newborns or even older humans.

Said Dr. Mills, "It’s all there for a purpose, though we’re still figuring out what that purpose is. So for God’s sake, please breast-feed."