Babies, Breast Milk, and Bifidobacteria

by Meghan Rosen

It does a body good.

Earlier this year, a London ice cream parlor debuted an attention-grabbing new flavor that made headlines around the world and sold out within days. The flavor, Baby Gaga, was infused with Madagascan vanilla and lemon zest and served in a martini glass chilled with liquid nitrogen. But at over $22 a serving, customers weren’t coming for its gourmet spices or upscale presentation; they were coming for its star ingredient, its claim to fame: human breast milk.

Just a week after giving birth, women who exclusively breastfeed produce, on average, more than 500 milliliters of milk per day. In parlor measurements, that’s about a pint of liquid. At 6 weeks, this amount has typically increased by about 50%; in some highly productive women, it can even double. For women with an abundant supply, excess milk can be drawn out with an electric pump and stored for future consumption (by baby, or in London, by high-paying ice cream connoisseurs.)

In an interview with the Daily Mail, the London parlor’s proprietor played up the novelty of his new flavor, but his description of its taste (‘creamy and rich’) was comfortably familiar. Flavor-wise, how does milk from humans compare to milk from cows? Can you even taste a difference? I don’t live in London, but I do have an ice cream maker. It’s in my freezer, right next to 2 liters of frozen breast milk.

Three weeks after the birth of my daughter, nightly pumping sessions left me with an unexpected, but not altogether unwelcome problem: I ran out of bottles to store milk in. (It’s not uncommon for women to produce too much or too little milk; it often takes weeks to establish a supply that matches the baby’s appetite.) After moving on to glass jars, ice cube trays, and finally, proper storage baggies, I had amassed enough milk to make more than 100 servings of ice cream (following Baby Gaga recipe proportions).

As bodily fluids go, breast milk is not an unlikely candidate for dessert innovation. After all, the most abundant component is sugar; the next is fat. Those two ingredients are about all you need to make a tasty frozen treat, and since a mother’s milk is steeped in the flavors, smells, and colors of what she eats, additives may even be unnecessary. A garlicky dinner, for example, predictably changes the taste of human breast milk, and babies tend to like it. One study even found that babies preferred their mother’s garlic-imbued milk to milk that was garlic-free.

After sugar and fat, the third most common component of human breast milk is not what you might think: it’s not protein, it’s not vitamins, in fact, it’s not even digestible by babies. Human milk includes a hefty proportion of molecules called oligosaccharides, or HMOs, (essentially long chains of simple sugars linked together in different conformations) that travel from the mother’s breast to the infant’s mouth and pass right on through its digestive tract.

Until recently, scientists considered these compounds just a bulky byproduct of lactation; after all, if it didn’t directly provide nutrition for the baby, what could it be good for?

But making milk isn’t free; for the mother, it’s actually quite expensive. It takes about 500 calories to fill and continually restock the breasts with a baby’s daily nourishment. Typically, a woman will burn fat stored during pregnancy or simply increase her food intake to meet the demand, but if she’s not getting enough nutrients, her body will tap into its own emergency reserves (like her bones or her teeth) to provide the baby with what it needs.

Rich milk makes for chubby, healthy babies, and healthy babies have a greater chance at survival, but it’s a finely balanced system: take too much from the mother and her health may be at risk. If every part of the milk comes at a cost, it’s unlikely that any part would be extraneous (especially those that are most abundant). Why waste the calories?

The initial understanding of HMOs wasn’t exactly wrong – babies can’t use the long chains of sugar as a source of nutrition – but it was missing one key point: other organisms can. HMOs may be indigestible by humans, but they’re the perfect food source for bacteria: in particular, Bifidobacterium longum infantis, a species that’s specialized to live in a baby’s gut.

Researchers at UC Davis have shown that bifidobacteria have a unique set of genes that is particularly suited for allowing growth in an infant’s intestine, where HMOs are abundant. Their work, profiled in the NY Times last year, helps explain why humans may have evolved to invest so heavily in a milk ingredient that is, for us, inedible.

Because bifidobactera thrive on HMOs, they have a leg up on other, less benevolent bacteria that are also clamoring for a home in the intestine. The well-fed bifidobacteria crowd out potential pathogens, effectively protecting the baby from infections. Breastfed babies tend to have fewer intestinal diseases and less constipation than their formula-fed counterparts: much of this is attributed to a gut full of beneficial bacteria living in harmony with their newborn human host.

Besides cultivating a community of ‘good’ intestinal bacteria, HMOs are also thought to trick ‘bad’ bacteria by mimicking the cells lining a baby’s gut. Instead of attaching to the baby’s cells and sneaking past its defenses to start an infection, pathogens bind to HMOs (which are replenished every time the baby nurses) and are flushed out with the waste.

Breast milk is tailor made for guarding a baby’s newly developing immune system, (according to the World Health Organization, it’s the best thing parents can feed their infants) and many people are willing to pay a premium for it. For mothers with milk supply problems, there’s an unregulated, craigslist-style market where human breast milk can fetch more than $2.50 an ounce, and women advertise their milk as ‘organic’, ‘vegetarian’, and, ‘free-range’. (The FDA does not approve.)

Human milk is a hot commodity, and not just for new parents. At, among buyer listings for ‘Local Milk’ and ‘Special Diet Milk’, there’s also a category for ‘Men Buying Milk’. (As of today, there were 17 buyers.)

Although breast milk is the gold standard for baby food, its cost can be prohibitive (unless you are making your own, human milk is much more expensive than formula), and its quality is not guaranteed (infectious diseases can be passed through milk, and there’s no screening in place to protect potential buyers). Current formula alternatives attempt to imitate human milk, but lack the immune-protective benefits and bacterial-promoting pre-biotics (like HMOs).

It might be possible, however, to create a more milk-like formula by studying human breast milk; this could give premature infants (whose mothers’ milk often takes longer to come in) a healthier start to life. Donated milk, however, is in short supply for milk-banks, and even shorter supply for research. A lactation consultant at UC Davis told me milk researchers on campus were always thrilled to receive human milk donations because they're not easy to come by. Unless, like me, you happen to have a freezer full of them. And live in Davis. For now, I think home made ice cream may have to wait.