Earlier this week, Nicholas Wade of The New York Times reported on a fascinating new discovery about the role of certain sugars found in human breast milk that play an important role in protecting the infants gut from dangerous bacteria.
While breast milk has been shown to confer a range of benefits to the baby, from protection against certain diseases to improved cognitive performance, the notion of a protective coating for the gut is something new. Indeed, one of the scientists working to "deconstruct" milk as part of his research is quoted saying that in this phenomenon of evolution, "mothers are recruiting another life-force to baby-sit for her baby."
The details of this three-way relationship between mother, child and gut microbes are being worked out by three researchers at the University of California, Davis — Bruce German, Carlito Lebrilla and David Mills. They and colleagues have found that a particular strain of bacterium, a subspecies of Bifidobacterium longum, possesses a special suite of genes that enable it to thrive on the indigestible component of milk.
This subspecies is commonly found in the feces of breast-fed infants. It coats the lining of the infant’s intestine, protecting it from noxious bacteria.
Infants presumably acquire the special strain of bifido from their mothers, but strangely, it has not yet been detected in adults. “We’re all wondering where it hides out,” Dr. Mills said.
The sugars are very similar to those found on the surface of human cells, and are constructed in the breast by the same enzymes. Many toxic bacteria and viruses bind to human cells by docking with the surface sugars. But they will bind to the complex sugars in milk instead. “We think mothers have evolved to let this stuff flush through the infant,” Dr. Mills said.
Dr. German sees milk as “an astonishing product of evolution,” one which has been vigorously shaped by natural selection because it is so critical to the survival of both mother and child. “Everything in milk costs the mother — she is literally dissolving her own tissues to make it,” he said. From the infant’s perspective, it is born into a world full of hostile microbes, with an untrained immune system and lacking the caustic stomach acid which in adults kills most bacteria. Any element in milk that protects the infant will be heavily favored by natural selection.
“We were astonished that milk had so much material that the infant couldn’t digest,” Dr. German said. “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.”
This program aired on August 6, 2010. The audio for this program is not available.