University of California researcher Bruce German has a lot to say on the subject of milk - specifica

University of California researcher Bruce German has a lot to say on the subject of milk - specifically, human breast milk. While all mammals produce milk, the makeup of the substance differs from species to species, as one might expect, to cater to that species’ needs. But in researching the composition of human milk, German found a surprise.

From the New Yorker:

Every mammal mother produces complex sugars called oligosaccharides, but human mothers, for some reason, churn out an exceptional variety: so far, scientists have identified more than two hundred human milk oligosaccharides, or H.M.O.s. They are the third-most plentiful ingredient in human milk, after lactose and fats, and their structure ought to make them a rich source of energy for growing babies—but babies cannot digest them. When German first learned this, he was gobsmacked. Why would a mother expend so much energy manufacturing these complicated chemicals if they were apparently useless to her child?

The answer, researchers found, is that these H.M.O.s travel into the large intestine, where they are fed upon by a microbe called Bifidobacterium longum infantis, which will cause them to grow faster and more efficiently than any other gut bacteria. This process is motivated by evolution, and is beneficial to both the bacteria and the child.

As [B. infantis] digests H.M.O.s, it releases short-chain fatty acids, which feed an infant’s gut cells. Through direct contact, B. infantis also encourages gut cells to make adhesive proteins that seal the gaps between them, keeping microbes out of the bloodstream, and anti-inflammatory molecules that calibrate the immune system. These changes only happen when B. infantis feeds on H.M.O.s; if it gets lactose instead, it survives but doesn’t engage in any repartee with the baby’s cells. In other words, the microbe’s full beneficial potential is unlocked only when it feeds on breast milk.

There are a number of other ideas as to why such a vast and diverse number of H.M.O.s exist in humans over other mammals. Some scientists suggest that feeding B. infantis helps to stimulate brain growth; others note that it serves as a defense against pathogens. At a pediatric hospital in California, these microbes might be a solution to help nourish premature infants.

To learn more about H.M.O.s and Bifidobacteria, visit the full New Yorker article here.