The Benefits of Human Breast Milk

Colonization of the human infants’ gastrointestinal tract by bacteria occurs only after birth. It is known that human breast milk encourages colonization of the newborn’s gut by beneficial bacteria and discourages colonization by harmful ones, but how exactly does it do that? An article in the Proceedings of the National Academy of Sciences provides a tantalizing glimpse into the likely mechanisms.

About 4-12% of the macronutrient composition of human milk consists of a structurally diverse group of complex sugars called oligosaccharides. These oligosaccharides are indigestible by the infant, and so for many years scientists thought they had no function. It turns out that they are digestible by a particular group of beneficial bacteria called bifidobacteria. The presence of these oligosaccharides in human milk gives the bifidobacteria a nutritional advantage over less desirable bacteria in the human infant’s gut. In other words, these oligosaccharides are produced in human milk specifically to provide nutrients to beneficial bacteria, rather than to nourish the infant.

Some of these oligosaccharides have another interesting property; they bind to certain harmful bacteria, thus preventing them from attaching to the epithelial cells lining the gut. Researchers think that these oligosaccharides may flush out harmful bacteria during that very vulnerable time in early life when the infant’s immune system has not yet developed fully.