Chasing Nature

by Adam Spangler
October 20, 2010

Researchers at the University of California, Davis, recently discovered a strain of bifido bacteria in the intestinal tract of breastfed babies that coats the lining of the baby’s gut and prevents disease-producing bacteria from getting through. Mothers are thought to be the source of the beneficial bacteria, but it has yet to be detected in adults. Where does it come from? How did it get there? Add it to the list of human milk’s unsolved mysteries.

Somewhere a biochemist sits, leafing through this newest human milk research and wondering if it will ever end. For more than a hundred years, industrious mothers, doctors, pharmacies, entrepreneurs, and corporations have been trying with varying degrees of success to perfect a manmade formula that mimics human milk. But human milk has been evolving for over 200 million mammalian years. Undaunted, the chemist rises from his chair and continues his pursuit—chasing nature but never catching up.

Formula generates billions of dollars in sales, but formula will likely never earn more than a silver medal, in part because manufacturers don’t know exactly what it is they are chasing. For starters, human milk not only changes from mother to mother but over the course of hours, days, weeks, months, even over the course of a single feeding. Determining its composition, much less recreating it in a lab, is an impossible task. But scientists persist in trying.

What makes human milk so special?
Scientists first discovered that human milk is mostly water (about 85 percent) and some combination of proteins, fats, carbohydrates, vitamins, and minerals. Milk production begins as colostrum, a thick, yellow liquid produced during pregnancy and the first days after birth—a high-protein mixture with less lactose (milk sugar) and a higher concentration of antibodies (proteins that protect against infection) than mature milk. Human milk’s ability to resist infection by boosting the development of the infant’s immune system may be the most important difference between formula and breast milk. Several days after birth, milk-producing cells begin to secrete mature milk—lower in protein and higher in fat, carbohydrates, and calories needed for energy and growth.

The changes that occur during feedings can be thought of as appetizer and entrée. First for the baby’s palate arrives foremilk, both watery and higher in sweet-tasting lactose. What follows is the hindmilk—thicker, higher in fat, and more filling. (Interestingly, nature didn’t make dessert).

That’s the basics, the very basics, because still in these fundamental ingredients there are unknowns as to the specific type, amount, ratios, and delivery system of each component, as well as what that means to the final product when it’s ingested and digested.

But it gets even more complicated. Human milk includes live cells and so-called “bioactive” compounds that pass from mother to child, sometimes in indigestible portions of breast milk that remain in the intestinal tract and do who knows what. This is where the front line of the research is happening now, and where formula makers are running into their largest obstacles to date as they tinker with their recipes. Getting certain protein ratios right is one thing; creating living cells (that could survive a shelf life no less) is still science fiction no matter the “complete nutrition” claims formula-makers market.

Mothers’ bodies create antibodies specific to pathogens and viruses that she has been exposed to and passes them to her child through her milk, and science can’t replicate that. Researchers can’t even tell you exactly what is in human milk, and why study after study show breastfed babies are routinely healthier with stronger development of cognitive, motor, visual skills, and immune systems.

Pharmaceutical efforts to replicate human milk highlight the complexity of this living fluid. For example, infants require a certain amount of iron. Formula contains substantially larger amounts of iron than human milk. Why? Doctors use the term bio-available or bioactive to describe the ease with which something is absorbed into the body’s system after ingestion. The iron in human milk is highly bio-available, so only small amounts need to be included. Iron found in formula is harder for the baby to absorb and it loses its effectiveness over time, so more iron is added to formula mixtures in an attempt to compensate for the lack of bio-availability and the time it takes for the formula to get from factory to baby.

Researchers will continue to examine human milk as a source of something completely new, something they didn’t know, some benefit that a manmade product simply can’t copy. In reporting about the UC Davis research, the New York Times interviewed two of the doctors who conducted the study. Dr. Bruce German called human milk an “astonishing product of evolution.” And as if there is any question about what is best for babies, Dr. David Mills added, “It’s all there for a purpose, though we’re still figuring out what that purpose is.”