Breast Milk: The Swiss Army Knife of Bodily Fluids

We here at mental_floss appreciate urine, and blood is vital. But for sheer versatility, you just can’t beat breast milk. So say scientists today in the journal Trends in Biochemical Sciences, who characterize the fluid as a food, a fertilizer, an umbrella, a clock, a remote control, and a wastebasket.

“Breastfed at Tiffany’s”—that’s the actual name of the journal article—compiles the findings of more than 70 research papers on breast milk and breastfeeding. While the research on the substance is plentiful, the chemistry of the stuff itself remains elusive. Most mammal milk contains around 30 to 50 different sugar molecules. Human milk has more than 200. This complexity is both fascinating and frustrating to chemists.

“Despite its recognized benefits, the structural richness of breast milk has also impeded the characterization of the multiple effects of milk components on infant physiology,” the authors write.

A new mother can make up to 4 1/2 cups of milk per day, a process that requires a tremendous amount of energy. But it’s worth it, the authors write, because of all the things breast milk can do.

To begin with the obvious: Breast milk is terrific nourishment for a fast-growing newborn human. In particular, the rich milk called colostrum, which a mother typically makes just before and after a baby’s birth, has high concentrations of proteins and beneficial carbohydrates.

Breast milk is also a form of protection for infant and mother. Studies have shown that “the ultimate personalized medicine,” as the researchers describe it, decreases infant mortality, can reduce a child’s risk of later obesity, and can even help protect mothers against later breast and ovarian cancer.

Breast milk also helps support the growth of healthy bacteria in a baby’s gut. At birth, each person is equipped with only the bacteria they collected as they exited their mother. (Some have suggested supplementing this bacterial load through a technique called "vaginal seeding," but the jury is still out on its effectiveness.) In order to protect yourself and develop a healthy microbiome, you’re going to need more than that, and you’re going to need to feed them. The plentiful sugar compounds in breast milk give brand-new baby bacteria the sustenance they need to survive and grow.

“Infants don't have the machinery to digest these sugars so they are literally for the bacteria,” paper co-author Thierry Hennet said in a press statement. “It's like a seeding ground, and breast milk is the fertilizer.”

And breast milk contains vitally important antibodies called immunoglobulins, as well as proteins called cytokines, defensins, and lactoferrins, all of which help strengthen and build a baby’s fragile immune system.

As a clock, breast milk helps regulate both hormone circulation in a woman and weaning in her baby. During pregnancy, an ebb and flow of hormones keep a woman from lactating too soon. Once the baby is born, chemicals in the milk itself trigger a decrease in those hormones, allowing a free flow of milk to the baby.

For milk sugars to be absorbed in the gut, they must first be processed by an enzyme called lactase. Our bodies make lactase until we’re around 2 or 3 years old. When that tap shuts off, the sugars proceed, unprocessed, into our gut, where they can cause bloating, cramps, and nausea (a.k.a. lactose intolerance). That intolerance is a not-so-subtle sign for a child’s body that it’s time to stop breastfeeding.

Breast milk also operates as a remote control for a baby’s growth. The hormones leptin, insulin-like growth factor 1, and adiponectin contribute to an infant’s fat storage, metabolism, and overall body growth.

Lastly, there’s the wastebasket function, which is as undesirable as it sounds. Harmful chemicals, including pesticides, heavy metals, and medications, can accumulate in a mother’s breasts and breast milk, then pass into her child.

Breast milk's other claim to fame? It influenced the scientific name for humans, mice, cows, weasels, and everything in between. According to the authors, “Breast milk is ultimately why Carolus Linnaeus, as the father of seven children, chose the term Mammalia to define our own class of animals in the tree of life.”

Of course, breastfeeding is not an option or the right choice for every mother. Experts agree that baby formula, designed specifically to meet infants' nutritional needs, is a safe alternative.