• 9 •
HOLY CRAP:
HERMAN, HAMLET, AND THE
ALL-IMPORTANT HUMAN GUT

O, thou with the beautiful face, may the child Reared on your milk, attain a long life, like The gods made immortal with drinks of nectar.

—SUSRUTA SAMHITA,
fourth to second centuries BC

LIMA HOSTED THE FIFTEENTH MEETING OF THE INTERnational Society for Research in Human Milk and Lactation during a cool austral spring week in October. The society’s cochair, Professor Peter Hartmann, welcomed me heartily. “We’ve never had a journalist before! Maybe you can tell people about our work!”

Hartmann, an Australian now in his seventies, is perhaps the world’s foremost expert in lactation. Even so, he bears the demeanor of someone whose work is largely unacknowledged outside this crowd. He’s a little bent over, and quiet, and a bit harried. He spent the week in Lima clutching his briefcase and scurrying from meals to meetings wearing his beret and a leather jacket. His son, Ben, is also here, not quite as stooped or as sartorial. Ben, thirty-four, runs a milk bank, collecting and storing donated human milk for use in the preemie ward of King Edward Memorial Hospital on the edge of Perth. (What is it with fathers and sons dove-tailing careers around breasts? Ben’s infant, Arlo Peter, has actively benefited from the Hartmann male tradition. “As my poor wife has indeed been subjected to the full barrage of tests by the research group, we certainly had a lot more information at our fingertips than most,” said Ben.)

I sat down with the elder Hartmann during one of the numerous café breaks in a heavily tiled, open-air meeting room at our faux-Renaissance lodge. Originally, he told me, he intended to study dairy science. He got a Ph.D. in bovine lactation. But then Britain changed its export policy, and the Australian dairy market “disappeared overnight,” he said. He secured a lectureship in biochemistry at the University of Western Australia in Perth, and in 1971, his first child was born. That event piqued his interest in the human side of things. He started studying progesterone withdrawal in women after birth, and found a large pool of enthusiastic breast-feeding volunteers through the Australian version of La Leche League. Human lactation was a tough academic sell, though. “Nobody was really interested when I applied for grants. It wasn’t a good career choice.” He smiled impishly, then added, “I proved them wrong.”

Still, he said, “It’s amazing how few people are interested in this incredible organ. The breast is the only organ without a medical specialty. It represents 30 percent of a woman’s energy output, and it’s not represented by a specialty! It’s absolutely appalling!” What he meant by the energy bit is that while a woman is lactating, the metabolic energy required to feed her infant is 30 percent of her total output—or the energy equivalent of walking seven miles—every day. Looked at another way, a male baby requires almost 1,000 megajoules of energy the first year of life. That is the equivalent of one thousand light trucks moving one hundred miles per hour. As the ecologist and writer Sandra Steingraber has put it, “Breastfeeding is a form of matrotropy: eating one’s mother.” No wonder so many women are ambivalent about doing it.

“It’s a magnificent organ to study from a molecular standpoint,” Hartmann continued, occasionally smoothing his trim white beard. “It’s easy to get access to it and harvest molecules. The problem lies with the view of it as an aesthetic breast. You only have to go to the local newspaper and see breasts hanging all over the place.” (Hartmann must be one of the few Western men on the planet who see this as unfortunate.) “The problem is the view of the aesthetic breast gets in the way of the view of the breast-feeding breast. The guys at the tennis club joke they wish they had my job, but no one is doing my job. At other [biological] meetings, you see thousands of scientists. We’ve got less than a hundred.”

He’s right that breasts are often overlooked, at least for noncancer scientific research. The Human Microbiome Project, for example, is decoding the microbial genes of every major human gland, liquid, and orifice, from the mouth to the skin to the ears to the genitals. It neglected to include breast milk, the life-giving, lifesaving, older-than-mammals-themselves elixir. Oops.

There is at least one entity very interested in Hartmann’s research, and that is Medela, the Swiss maker of breast pumps. The company sent a number of representatives to Lima, and they presented a poster explaining their latest product. It’s a new artificial “teat”—that’s Australian for nipple—based entirely on Hartmann’s lab studies regarding flow and suction. I know a thing or two about suction. Just talking about it makes me wince. The new teat is meant to be used with Medela bottles filled with pumped human milk.

The Hartmann lab in Perth is well regarded for upending prior notions of how sucking—technically, suckling—works. Experts used to think the infant squeezed the nipple with her tongue, rhythmically releasing milk through this peristaltic action, a bit like wringing a washcloth. But Hartmann and his colleagues, using high-tech ultrasound videos, showed that the baby forms a strong suction with her lips, and it’s when she releases the nipple that milk flows down her throat (and moreover, this being a specialized human infant, she can suck and breathe at the same time, unlike adults).

One day some years ago, Hartmann was flying over Australia, and he found himself gazing out at giant ore piles near the mines. They were large mounds of salt and minerals, smooth and gently rounded. They looked like … his favorite organ. From high in the sky, a stockpile looked just like a breast from a few feet away. It occurred to him that it might be possible to apply giant-earth stereoscopic measuring techniques to the human breast. But he wasn’t merely interested in measuring the volume of a breast; he wanted to measure the synthesis of milk.

“Humans do not produce milk at full capacity, like a dairy cow,” he said. “They down-regulate to match the baby’s appetite. So we had to learn about those differences. How do you measure milk synthesis in a woman? I thought maybe if you could measure the volume of the breast, you could measure synthesis.” So he approached an expert in a mine-measuring technology called Moiré topography, and together they figured out how to calibrate units in something other than metric tons. They call it CBM, for computerized breast measurement, and it has to do with projecting light stripes at an angle onto the breast. “The distortion of the stripes could let you work out the volume of breast!” said Hartmann. “We could do it before and after feeds over a twenty-four-hour period. The difference in volume is the short-term synthesis [of milk] from one breast-feed to another!”

In the old days, people used to measure milk output by simply weighing the baby before and after a feed, but that didn’t reveal information about the workings of each breast independently, or about how much milk a breast could make from hour to hour or day to day. These data could be useful to hospitals, doctors, and, of course, Medela, which funded the research. In a paper describing the work, Hartmann and colleagues found that each breast of the average new mother produces approximately 454 grams, or 16 ounces, every twenty-four hours. Each breast can store about half of that, and both actions are determined by the demand of the infant (one baby in the study ate twice the average). Check this out: even after fifteen months of lactation, each breast can still make 208 grams of milk, even though the breast has returned to its pre-pregnancy size. In other words, the breast becomes more efficient, possibly owing to a “redistribution of tissues within the breast,” according to the paper by Hartmann’s lab. Breasts should get an Energy Star rating.

In any case, thanks to Hartmann, no longer is the dairy machinery such a mystery.

But the dairy product still is. I wanted to find out more. What makes milk so special, if it really is? A lot of Hartmann’s work is in the liquid physics arena, but many of the Peru attendees were molecular biologists, biochemists, or geneticists who are deconstructing the components of milk bit by bit. They’ve been doing this for well over thirty years, and you’d think they’d have figured it out by now. Until very recently, it was thought that breast milk had around two hundred components in it. These could be divided into the major ingredients of fats, sugars, proteins, and enzymes. But new technologies have allowed researchers to look deeper into each of these categories and discover new ones altogether.

Scientists also used to think breast milk was sterile, like urine. But it turns out it’s more like cultured yogurt, with lots of live bacteria doing who knows what. These organisms evolved to be there for a reason, and somehow they’re helping us out. One leading theory is they act as a sort of vaccine, inoculating the infant gut so it can recognize bad actors and fight them when the need arises. At the conference, Mark McGuire, another former dairy scientist recruited to the human lactation field, described how he took forty-seven samples of milk, extracted DNA, and identified eight hundred (yes, eight hundred) species of bacteria living there, including small amounts of staph, strep, and pneumonia, all of which normally live in our bodies. An individual milk sample has anywhere from one hundred to six hundred species of bacteria. Most are new to science.

Then take the sugars. There’s a class of them called oligosaccharides, which are long chains of complex sugars. Scientists have identified 140 of them so far, and estimate there are about 200 of these alone. The human body is full of oligosaccharides, which ride on our cells attached to proteins and lipids. But the mother’s mammary gland cooks up a unique batch of “free,” or unattached ones and deposits them in milk. These are found nowhere else in nature, and not every mother produces the same ones, since they vary by blood type. Even though they’re sugars, the oligosaccharides are, weirdly, not digestible by infants. Yet they are a main ingredient, present in milk in the same percentage as the proteins and in higher amounts than the fats. So what are they doing there?

They don’t feed us, but they do feed many different types of beneficial bacteria that make a home in our guts and help us fight infections. In addition to recruiting the good bugs, these sugars prevent the bad bugs from hanging around. They act as “anti-adhesives,” kicking the bad guys off the gut surface. Some also seem to handcuff themselves to the criminals and escort them off the premises like a micro paddy wagon. “I think the benefits of human milk are still underestimated,” said Lars Bode, an immunobiologist at the University of California, San Diego. “We’re still discovering functional components of breast milk using new technologies and using smaller amounts of milk.”

Bode told me it’s well established that premature infants do remarkably better—as in, an order of magnitude better—on breast milk than on formula. As we’ve been able to keep younger and younger preemies alive, they’re more likely to be very sick. About 10 percent of preemies will suffer from a dreadful disease called NEC, or necrotizing enterocolitis, and about a fourth of those will die from it. NEC is a gut infection that causes the lower intestine to shrivel up and die. Babies who survive this often must have the necrotic portion surgically removed, leaving them with a condition called shortgut syndrome. Because they can no longer adequately digest food, they spend the rest of their lives attached to an IV. But the incidence of NEC is 77 percent lower in breast-fed babies than in formula-fed babies. This is why neonatal units work so hard to get mothers to pump breast milk for their preemies’ feeding tubes. In lieu of that, they use donated milk from milk banks, and in lieu of that, they can buy a newfangled “fortifier” made from concentrated human milk by a company called Prolacta Bioscience. It costs $12,000 per baby.

Naturally, conventional formula companies are falling all over themselves to synthesize these unique human sugars and add them to their cow-milk products. So far, they’ve been able to re-create only a few of the simpler ones, and to not much effect. These newly enriched formulas, for example, do not alter preemie NEC rates, according to Bode. This is because the most “bioactive” molecules are the bigger, more complex oligosaccharides, which are incredibly difficult to make in a lab. “Take one of these special monosaccharides? If you wanted to supplement human milk with it, the package would cost half a million dollars,” he said.

Bode said his lab has also shown that a simpler chain, called GOS, is effective at fighting amoebiasis, a parasite that kills 100,000 people a year. It’s likely GOS could help adults as well as babies.

THE GUT, IT TURNS OUT, IS INCREDIBLY IMPORTANT NOT JUST TO infant health but to adult health as well. Bruce German, a food chemist from the University of California, Davis, drove this point home for me. Picking up the breast ball where the Human Microbiome Project dropped it, German is spearheading the Infant Microbiome Project at the university’s Foods For Health Institute. The idea is to map and characterize oligosaccharides, as well as other human milk components, for eventual infant and adult medical applications. As German put it in a recent video, “We’ll take little tiny droplets of milk and disassemble them completely, understand every single molecule in it … and how they function when ingested by infants… We’re confident it will teach us how to prevent diseases like diabetes and heart disease and ultimately even cure diseases like cancer.”

German speaks in superlatives and alluring metaphors even when he’s not being filmed. “The genomic tree of life is a compelling one,” he told me in a private mini-lecture on microflora over breakfast one morning. A wiry, almost hyper speaker, he began to turn red. “We’re just a tiny branch! The rest of it is all microbial! We’re just a small part of the mass of microbial life. To a large extent, we live our life at their say-so. We have to form a pact with the world around us. Recruiting protective microflora is the very first thing we do in life.” He wasn’t eating, but now he sipped his coffee. “Put yourself in the mindset of an infant. You’re born, you are dropped in the mud, literally, where the microbial community thinks of us as lunch. So you must develop a community that protects you for life.”

He continued in his riveting, pretend-you’re-a-baby mode. Clearly he’s a man used to speaking to glassy-eyed undergraduates. “If you’re a preemie and you probably came out by C-section and you’re not breast-fed, you’re acquiring bacteria in your gut from the hospital that will reside there for the rest of your life.” He winces. “That’s not the way you want to do it. Normally, the mother hands down bacteria to her infant by means we still don’t fully understand. If there’s a successful transfer, it will be handed down mother-todaughter for generations. Now we think one C-section could break that chain.” He plunks down his coffee cup. “You’ve lost touch with your genetic ancestry.”

Could another way to break the microbial chain occur if the mother herself was not breast-fed? Are we now looking at a couple of generations of orphaned intestines, cut off from their full bacterial legacy? I asked German and he nodded. “Exactly.” He said he’d like to see every baby (who doesn’t receive breast milk) get a dose of Bifidus infantis at birth, like a vitamin K shot.

This bacterium is one of German’s favorites. Bifidus infantis has seven hundred genes, all of which evolved to live and thrive in a unique microbial environment: the infant gut. There, B. infantis eats the oligosaccharides that rain down in breast milk. The bacterium produces proteins that pull those special sugars inside it, where they get broken down and digested so that they are unavailable for other (worse) bacteria. Furthermore, said German, “Bifidus can overwhelm bad bacteria. It recruits a whole schoolyard of supportive organisms.” As I’ve said, these human milk oligosaccharides are not found anywhere else in nature. “It’s clear that these bacteria co-evolved with our oligosaccharides,” continued German. “It’s our true symbion.”

It’s good to know all this, but it’s also another intense failing for modern mothers to feel guilty about. I couldn’t help but wonder if I’d somehow flubbed the important microbial hand-off to my children. Some of the blame I could cast to my mother, who might not have given me the adequate goods in just four weeks of nursing. But I get a pit in my stomach when I think of the repeated rounds of antibiotics I took for mastitis while nursing my son: cephalexin, amoxicillin, dicloxicillin. Was I killing off everything good in his gut as well as in mine?

The adult gut can recover from antibiotics within a few months because of mysterious reserves of bacteria in our bodies, our housemates, and to some extent, our food. But the infant, who is bacterially “naive” and building colonies for the first time, might not. These thoughts snowballed in my mind, because my son has had gastrointestinal trouble for most of his life. The poor guy is chronically constipated. One pediatric gastrointestinal specialist I took him to shrugged off a search for root causes, saying, “Well, some people just have slow motility, like a sloth.” That’s my son, the sloth.

I sought out David Newburg, a biologist from Boston who has been studying the connections between breast milk, intestinal microflora, and disease for over two decades. A tall, tanned man with a trim goatee, I often saw him enjoying the Peruvian pastry table, as did I.

“Can I ask you a personal question?”

Newburg raised his eyebrows. “In that case, I’m going to need two tea sandwiches,” he replied.

I told him the story of my mastitis and the antibiotics. Was my son’s problem my fault?

“It’s definitely possible,” he said, making me feel wretched. Good tests to diagnose the gut’s array of normal and abnormal microflora are still a few years out, he explained. Changing the microflora is even harder. Someday, though, these things will be a routine part of medical care. In the meantime, Newburg recommended Ben regularly take probiotics (such as the lactobacillus found in yogurt and supplements) as well as eat foods rich in prebiotics (the complex carbohydrates that beneficial bacteria need to thrive). Although breast milk is the world’s best source of prebiotics for humans, they can also be found in Jerusalem artichoke, Belgian endive, onions, asparagus, and some other plants not terribly alluring to a nine-year-old.

I told Newburg what Bode had said about it being so difficult and expensive to synthesize human-milk prebiotics.

“Hah!” said Newburg, baring a little professional rivalry. “We know how to do it. Come visit my lab. We’re up to our necks in shit.”

I know, most people would have declined this offer and fled. But by now I had fallen too far down the milky rabbit hole and was weirdly entranced by gut flora, that unexpected and invisible pillar of human health. I kept thinking of German’s image of us living at the behest of the microorganisms, not the other way around— “Who’s really cultivating whom?” he’d asked dramatically. The microflora outnumber us by a lot. There are ten times more microbacteria in our guts than there are cells in the human body. A song lyric kept playing in my head: Patty Griffin’s “You are not alone.”

And so, a few weeks later I was negotiating the steep, rainslicked steps outside of Higgins Hall on the Boston College campus. I maneuvered past a rather severe statue of St. Ignatius and into the new and immaculate molecular sciences building, where Newburg commands a spacious realm on the fourth floor.

Wearing black jeans, a black golf shirt, and sandals, Newburg welcomed me into his lab. It looked like a cross between a kitchen and a Kinko’s. The boxy, beige machines are actually mass spectrometer contraptions, such as the snazzy new “triple quad.” It sounds like a Vail chairlift and looks like a photocopier, but it costs around half a million dollars and breaks down molecules into gradually smaller components. To distinguish and identify different molecules, these machines utilize color, molecular weight, or, my favorite, “time of flight.” This one sends molecules pinging down a zigzag chamber and then up a small cylinder the size of a stovepipe. No two longchain molecules make the lap (or, technically, have the same mass-to-charge ratio) in exactly the same way. Many of the substances Newburg is finding in human milk have never been seen before.

The lab is a bank for two main kinds of substances: human diseases and the breast milk that fights them. To obtain the diseasecausing organisms, Newburg collects infant feces. He and his colleagues isolate the pathogens (such as botulinum, campylobacter, Vibrio cholerae, and Escherichia coli) and grow them in an anaerobic chamber similar to our guts. He especially treasures a source in Mexico, a clinic that sends him samples rich in things like rotavirus. Otherwise, he finds them through local hospitals and lactatingmom networks. “Just to handle baby poop is an incredibly long and complex process,” he said, involving informed-consent paperwork and hospital review boards. Some of his fecal freezers are set to –80 degrees Celsius, the temperature of outer space. Other incubators mimic body temperature for growing human cells from the lining of intestines and lungs (breast milk is also ferociously adept at fighting pneumonia). Leaving the tissue culture room, I saw a tube the size of a beer glass stuffed with what looks like raw steak. “That’s a liver,” said Newburg.

For him, analyzing baby shit is practical and urgent. Globally, 1.4 million children under five die each year from diarrheal illnesses. This makes sense if you consider that 20 percent of the world’s population doesn’t use any sort of toilet, and nearly half doesn’t have access to decent sanitation. Nearly a billion people don’t live near clean drinking water. At the same time, human milk is so effective at fighting infections that if all children were exclusively breast-fed the first six months of life, one in five childhood deaths could be prevented.

“Breast-fed poop doesn’t smell too obnoxious,” Newburg said. “It’s more like sour cheese or milk. Frankly, even as a guy, I got used to it.” Newburg led me to a normal-looking fridge to show off some of his precious collection, but he gasped when he saw the door was slightly ajar. A box of test tubes was wedged clumsily into the door. A small puddle had formed on the floor below it. “Oh no,” he said. A lab tech had accidently left the door open overnight. It occurred to me that the only thing worse than a freezer full of poop was a freezer full of thawing poop—especially for Newburg, who would have to deal with the scientific consequences. He lifted a test tube packed with brown goo and shook it. “I think this whole fridge is compromised,” he muttered.

After he washed his hands, we settled into his adjacent office for a chat. A poster-sized, soft-focus photograph of a blonde woman nursing a baby loomed above his desk (“My wife doesn’t like it,” he said of the image). Books such as Phospholipids Handbook, Gray’s Anatomy, and Modern Nutrition in Health and Disease packed the front wall. Like many men in this field, Newburg told me he didn’t start out intending to study lactation. His field was neuroscience. But running a rat experiment three decades ago, he noticed his formulafed pups “never performed as well as the nursed ones. A normal person would have said, ‘fine,’ but not me. I took a sabbatical to study essential nutrients for brain development,” and the rest is history.

He became intrigued by the indigestible oligosaccharides, and soon he had established that they must function to fight pathogens in the infant gut. In the 1980s, his lab (then at Harvard) rather startlingly discovered that human milk inhibits the transmission of HIV, among other things. He didn’t know exactly how, and he still doesn’t, although he’s closer to knowing which oligosaccharide compound is responsible. “We do know that the transmission of HIV through milk is much less than through any other medium,” he said. He fully expects to identify the heroic sugar complex, then make it and offer it up as a therapy in the real world. “We’ll study it and we’ll find out,” he said. “It would be much more effective than a vaccine, I think.”

Already, Newburg’s company, Glycosyn (he cofounded it in 2002), is making a “2-linked fucosyloligosaccharide” known to help ward off norovirus, E. coli, cholera, and campylobacter. Because, as Bode pointed out, it’s too expensive to synthesize these molecules from scratch, Newburg has a different strategy. He’s teaching yeast to produce them for him by converting a natural product they make into a building block called fucose. He then takes that and links it to lactose “because that’s what mom does.” Some other companies in Europe are making oligosaccharides from plants or cow’s milk and putting them in infant food, but Newburg says it’s not the same.

Glycosyn will start testing its product in humans sometime in 2012 or 2013. Newburg told me the final product will probably resemble a sugar packet that can be mixed into food or formula. It will be ideal for babies on formula or babies and toddlers who are weaning, which can be a treacherous process in developing countries with unsafe food and water. Newburg’s product will be like NutraSweet for the survival set, the mysterious stuff of breasts purified into a paper packet.

As someone who extols the benefits of breast milk but wants to improve formula, Newburg has garnered some criticism from both sides. If there’s one thing the lactivists hate, it’s better formula, because they think it can never really be good enough. “It’s frustrating to see moms who don’t breast-feed, but I understand why some don’t,” said Newburg. “I don’t think their children should be punished. My orientation is to the baby.”

LECHISTAS, PREPARE YOURSELVES: FORMULA WILL GET BETTER and so will a bunch of other foods, supplements, therapies, and medications thanks to the unlocked secrets of milk. A quick survey of what other biotech companies are doing shows the range of benefits being urgently, greedily, attributed to human milk. It’s important to remember from chapter 2 that lactation likely evolved from the immune system; its primary function was not nutrition but protection. Most of the cells in milk are macrophages, which disable viruses, fungi, and bacteria. I already mentioned Prolacta Bioscience, which is concentrating and pasteurizing donated human milk—and then selling it—as an “immunonutrition” supplement for preemies weighing less than 2.5 pounds. In the Brave New World department, several companies are reengineering other animals to produce the unique ingredients of human milk, because it’s still easier and cheaper to raise a herd of transgenic goats than it is to beg or buy large quantities of milk from suburban mothers.

One of the most sought-after components of human milk is a glycoprotein called lactoferrin. Known to have keen anti-inflammation, antioxidant, and anti-infective properties, it’s an iron-binding machine that outcompetes pathogens. Lactoferrin can also be found in tears and saliva and genital secretions, but in tiny percentages compared to milk. It’s possible to inject animal embryos with the human gene that makes it. Some companies are genetically altering cows, goats, and even rabbits, then isolating the human lactoferrin from the milk. One Japanese company has begun marketing capsules, which it calls “Lactoferrin Gold.” Three liters of modified cow’s milk are needed to make one capsule. I can see why they named it after a precious ore. To make lactoferrin, another company bred a whole herd of cows from one long-dead transgenic bull named Herman. But altered mold fungus can make it too. A biotech outfit with over a hundred lactoferrin patents intends to use the fungal product for fighting cancer and healing wounds.

According to one economic analysis, if lactoferrin were added to infant formula, it would create an extra $15 billion in value. If added to eye drops, oral hygiene, soaps, and shampoos, another $10 billion. Cancer drugs: $19 billion.

That’s just lactoferrin, but there is also active research on other components. Stem cells, for example, teem from human milk, particularly from the dense colostrum produced in the early days of nursing. Before the baby is five days old, she’ll receive five million stem cells from the mother. No one really knows why. Are they colonizing the baby in case she needs them? Are they just a by-product from the newly functional mammary gland? Then there’s a very cool protein called alpha-lactalbumin. In the acids of the infant stomach, the protein refolds itself and picks up a neighboring fatty acid, also from the milk, forming a new complex. The scientist who discovered it fifteen years ago, a Swede named Catharina Svanborg, dubbed it HAMLET, for human alpha-lactalbumin made lethal to tumor cells.

This HAMLET ditches the pretty soliloquys and dons a superhero cape, diving into the nuclei of malignant (and viral) cells and freezing the gears. It effectively prevents malignant DNA from replicating and then in a final grand stage gesture causes the cells to implode. Weirdly and auspiciously, it seems to destroy only bad cells, leaving the good ones alone. Laboratory experiments have shown that HAMLET kills forty different types of cancer cells in a dish, including those of the bladder, lymphoma, skin, and brain, but it has not been tested much in humans yet. Still, the reason Svanborg began looking at milk is that several studies found that formula-fed children have significantly higher rates of childhood lymphoma than their breast-fed peers.

All this ought to make nursing mothers feel a little more valuable. Maybe they’ll wise up and start registering with insurance companies as health-care providers. Or maybe they’ll join the rawmilk underground. A few already have: an Internet site called Only The Breast lists classifieds with wording like “scrumptious mommy milk.” At four dollars per ounce, it costs 262 times the price of a barrel of oil. The marketplace for human milk in most of the United States and in the rest of the world is unregulated so far, despite the fact that it’s capable of transmitting hepatitis and other maternal diseases along with lactoferrin. Nonprofit human milk banks (there are eleven in North America) heat the milk to pasteurize it, but the process also kills some of its bioactive ingredients. While donor milk is used mostly in neonatal intensive care units for preemies, older children and adults sometimes buy it for treating various illnesses or for soothing the harsh mucosal effects of chemotherapy.

As Bruce German had reminded me in Peru, these breakthroughs in the understanding of milk are not just interesting; they are fundamentally altering what we know about human health. “The story that is compelling to me is the fascinating interplay between bacteria and humans,” he’d said. “This whole story is part of a revolution in science itself, where the chemistry-dominated science of the twentieth century is giving way to the biology-dominated science of the twenty-first century. Such a shift is sometimes difficult to appreciate, especially for people outside the scientific community. For milk and bacteria there is an easy point of entry for people to see the vivid contrast: twentieth-century chemistry—use chemicals to kill all bacteria; twenty-first century—use biomolecules and organisms to guide a supportive microbial ecology. It’s a new world of science.”

NATURE HAS DESIGNED MILK TO BE INGENIOUS, BUT IT’S THE breast itself that directs the show. Biologists bat around the concept of “crosstalk,” how one part of the body communicates with another and vice versa. In the case of the lactating breast, the organ is communicating not only with its immediate landlady but also with the infant. From the very beginning, the breast appears to know whether the infant is a boy or a girl, at least in rhesus macaque monkeys, which have similar milk to humans and have been studied more comprehensively than their human relatives. In the macaques, mothers of sons produced fatter, more-energy-dense milk. Katherine Hinde, a professor in the human evolutionary biology department at Harvard University, thinks this might be because macaque males have slightly higher growth rates and as adults weigh about 30 percent more than females (human males weigh about 15 percent more than females). But Hinde has another, more devious social theory as well. She discovered that macaque mothers produce fattier milk for sons, but they make more milk for daughters, meaning the maternal energy investment is about the same. In that matrilineal primate society, daughters learn from hanging around their mothers longer and more often, and thinner milk means they stay close for more frequent feedings. The sons, by contrast, might be “tricked” by the mother’s fattier milk into feeling sated and therefore not feeding as often. It’s not a bad thing for the sons; they have more time to play and explore, skills they’ll need down the road when they leave the group.

How does the breast know whether the infant is male or female? Probably because hormones called placental lactogens talk to the breast during pregnancy, when it is building the structures it will need for making milk. Girls evidently get the skim-milk machinery. Mom wants to produce good milk, but she doesn’t want to kill herself doing it, which brings up an interesting dynamic between mother and infant: competition. Babies have evolved their own tricks to get as much of their mother’s resources as they can: Witness the tightly interwoven placenta (made by the embryo) that becomes essentially parasitic. The mother’s body has genes to expel the fetus a little before the due date. The baby’s genes—put there by the father, presumably—tell it to stay put a little longer.

The breast picks up the tug-of-war after birth, slipping endocannabinoids into the milk. Note the root cannabis in there. These substances, which cause the munchies, probably play a role in enticing infants to eat. But they also regulate appetite so infants feel very full by the end of a feed and thus don’t eat too much. Interestingly, formula lacks these compounds, and formula-fed babies have a notoriously higher caloric intake. It’s one of the speculations about why we have a childhood obesity epidemic.

While looking out for the mother, the breast is also looking out for the baby. It is constantly sussing out his or her nutritional and immunological needs. When the breast senses an infection brewing in the baby, it somehow tips off the mother’s immune system and in turn the milk puts out more lactoferrin and the relevant antibodies. When the baby is older than one year, the milk contains more fat and cholesterol to match the baby’s energy needs. When a baby is born prematurely, the mother’s milk, as if anticipating its role, contains more protein and caloric density for a tiny tummy. Is it a coincidence or did we evolve that way, despite the unlikelihood that many preemies survived in our early history?

The breast is like a smartphone and juice bar in one. It communicates with the mother’s body, the baby’s body, and the environment. The breast knows the condition of the mother. Stress, for example, can cause her to hold back her output of milk. It can also send more cortisol into the milk, which appears to affect the longterm personality of sons (but not necessarily daughters), perhaps making them more exploratory or hypervigilant to grow up in a difficult environment. We know that a tough environment can affect a mother’s stress levels. After the terrorist attacks of 9/11, many new mothers all over the country experienced temporary problems producing enough breast milk. My son was eight weeks old. Looking back, I wonder if this event played a role in our early difficulties with supply and demand. Unlike my mother, though, I never kept a nursing log.

Cells in the breast communicate with cells in the bone, telling the bone how much calcium to release for milk production and when to start guarding it again. A mother loses up to 6 percent of her calcium for her baby, but the stock more than fully replenishes within a few months after weaning. In terms of things like energy and minerals, breast-feeding takes a severe toll on mothers, though not as severe as the toll of gestating and delivering a fetus. Breast-feeding actually helps the mother recover from these events by tweaking her metabolism and protecting her heart. It’s a critical part of how the enterprise was designed for our benefit as well as our baby’s.

Internist and researcher Eleanor Schwarz had told a story in Peru about her inspiration for a study. “I was storing some of my milk in bottles in the refrigerator, and I noticed it looked like buttermilk,” she’d recalled. “That’s how fatty it is. Was there some relationship between the bottle of butter I was storing in the fridge and my future cardiovascular risk?” In other words, was the fact that her body was mobilizing her fat and siphoning it into milk helpful to her arteries or not? Some studies had shown that women who breast-feed lose more pregnancy weight than mothers who don’t, but the data were inconsistent, and there wasn’t much information about types of fat they lose or where it came from in their bodies.

Schwarz started crunching the numbers from the giant data set of the Women’s Health Initiative, a long-term national health study. She found that while there wasn’t much difference in weight loss between mothers who did and didn’t breast-feed, women who didn’t were 10 percent more likely to suffer cardiovascular disease and type 2 diabetes later on. She examined numbers from another study of 100,000 slightly younger women and found that those who breast-fed for just three months had a threefold lower risk of aortic or arterial calcification after adjusting for other lifestyle and economic factors. While pregnancy itself had put these women at risk for weight gain compared to women with no children, lactation had returned their lipid profiles back to baseline, a benefit that remained for decades. Mothers who nursed their babies also had less belly fat, which is known to be linked to heart and metabolic problems. “My current thinking,” Schwarz concluded, “is that humans are mammals, and never lactating is not normal. I think breast-feeding plays an important role in a woman’s recovery from pregnancy. It’s like liposuction in terms of how much fat it’s pulling off the body.”

A NURSING MOTHER, OF COURSE, HAS NO IDEA ALL THIS CROSStalk is going on. She just knows her baby is hungry, and she can help. But food is a powerful currency. Add some hormones and she’s a goner. Within hours of birth, my son and I (and then my daughter and I) became what scientists call “the mother-infant dyad”—a fully self-contained unit. For us, the hinge of it was a pair of breasts. Knowing that I could give my babies all they needed was nothing short of astonishing. Through breast-feeding, I grew more confident in my ability to be a mother.

Unfortunately, not many mothers get this far. For such a clever, highly evolved system, it’s too bad that breast-feeding is so ridiculously hard to do. I recently chatted with a young mother at a family gathering. Her eight-week-old baby girl was swaddled in pink, happily sleeping in her arms. “I tried breast-feeding for five days,” said the woman, “but then the pain started. I was like, “that’s it, I’m done.” She’s not alone; approximately 80 percent of newly lactating mothers have sore nipples, and many of them quit at the first sign of discomfort.

The big contradiction is that breast-feeding is so natural, and yet so completely unintuitive. What’s really natural is for women to have a love-hate relationship with it, and this is something the lechistas don’t tend to admit. Just as we’ve evolved to breast-feed, we’ve also evolved to be flexible, even whimsical, in our feeding habits. Some cultures and individuals nurse their children for years; others, not at all. In fact, humans are the only primates who wean their young long before they can forage on their own. We do this because we can, not because it’s always the best thing for the baby.

Anthropologist Dan Sellen from the University of Toronto, who was also in Peru, said that most humans in foraging cultures weaned their young at about thirty months, “a pattern known to be optimal for growth and development.” But there were always outliers—societies where the norm was nursing much further out or for much shorter periods. This flexibility—born from our human opportunism—may be natural, but it may also be problematic at the extremes enabled by manufactured formula, according to Sellen. As he pointed out, early weaning is sometimes okay from a nutritional perspective, but less so from an immunological one, especially as you look globally. When I returned from Peru, he sent me a recent paper of his. Its conclusion: the “mismatch between optimal and actual infant feeding practices in contemporary populations is widespread and presents a major public health challenge.”

In a book about the unnatural (as well as the natural) history of the breasts, here is where we must deliver some more sobering as well as some strange news: not only is breast-feeding hardly practiced these days the ways nature intended, but the very stuff itself is oddly compromised.

In a great paradox of modern life, just as we’re on the brink of truly understanding what’s in human milk that can help us, the components are shifting.

As of late, breast milk has an unanticipated, new, ingredients label.