What if our breastmilk has evolved not only to nourish human infants, but also equally importantly to feed a very important microbe? From an evolutionary perspective, this makes sense. The healthy commensal bacteria living in human digestive tracts provide us with valuable benefits that we cannot provide ourselves. Nourishing probiotic bacteria helps grow healthy babies.
Researchers at the Foods for Health Institute at the University of California, Davis have been exploring this issue. Chemist Bruce German is leading this effort.
Breast milk has over 250 compounds called human milk oligosaccharides, or H.M.O.s. In fact, they are the third most plentiful ingredients found in human milk. The puzzling thing about this is that human babies cannot digest H.M.O.s. Why would the human body go to such effort to produce them in the milk if the baby cannot digest them? If they provided no benefits, one would expect that evolutionary pressures would have discouraged them from remaining as a component in the milk in such high numbers.
Breastfed babies have very high levels of Bifidobacterium in comparison to their formula-fed peers. It turns out that one particular bacteria subspecies thrives on H.M.O.s – Bifidobacterium longum infantis. Perhaps unsurprisingly, studies have shown that B. longum infantis does several things which are really beneficial for human infants.
When B. infantis digests the H.M.O.s, it produces short chain fatty acids. The babies can digest these helpful compounds and are nourished by them.
One thing that distinguishes humans from other mammals is our large brains. Sialic acid is necessary for brain growth. When B. infantis digest H.M.O.’s they produce sialic acid as a byproduct. Could it be that these microbes are partially responsible for encouraging human intelligence?
When the healthy microbes make contact with the cells in the digestive tract, they prompt them to produce adhesive proteins that decrease the permeability of the gut lining. This means that it is harder for pathogens to enter the body from the digestive tract and thus reduces illness and disease.
B. infantis can survive in the digestive tract without H.M.O.’s, but in the absence of exposure to breast milk, this microbe provides none of the beneficial effects outlined above. Supplementing formula-fed babies with B. infantis in the absence of breast milk will provide them with no benefit.
Mark Underwood is a pediatrician at U.C. Davis Children’s Hospital. He is making practical use of Dr. German and his colleagues’ research. To encourage healthy growth in babies that are born very prematurely (and have been given lots of probiotic bacteria-killing antibiotics as part of their delivery), he is giving them a combination of donated breast milk and B. infantis. Previous experiments that gave such babies probiotics alone had limited success, but Dr. Underwood believes that giving the bacteria along with their favorite food will have a much better outcome.
To read more about this exciting research, you can read an excerpt from “I Contain Multitudes: The Microbes Within Us and a Grander View of Life,” by Ecco, an imprint of HarperCollins Publishers that is published in the New Yorker Magazine on July 22, 2016