• Muunuu

The answer to lactose intolerance might be in Mongolia

In July 2017, archaeogeneticist Christina Warinner headed there to learn about the population’s complex relationship with milk. In Khatgal, she found a cooperative called Blessed by Yak, where families within a few hours’ drive pooled the bounty from their cows, goats, sheep, and yaks to supply tourists with heirloom dairy products.

Warinner watched for hours as Blessed by Yak members transformed the liquid into a dizzying array of foods. Milk was everywhere in and around these homes: splashing from swollen udders into wooden buckets, simmering in steel woks atop fires fueled by cow dung, hanging in leather bags from riblike wooden rafters, bubbling in specially made stills, crusting as spatters on the wood-lattice inner walls. The women even washed their hands in whey. “Working with herders is a five-senses experience,” Warinner says. “The taste is really strong; the smell is really strong. It reminds me of when I was nursing my daughter, and everything smelled of milk.”

Each family she visited had a half-dozen dairy products or more in some stage of production around a central hearth. And horse herders who came to sell their goods brought barrels of airag, a slightly alcoholic fizzy beverage that set the yurts abuzz.

Airag, made only from horse milk, is not to be confused with aaruul, a sour cheese, created from curdled milk, that gets so hard after weeks drying in the sun that you’re better off sucking on it or softening it in tea than risking your teeth trying to chew it. Easier to consume is byaslag, rounds of white cheese pressed between wooden boards. Roasted curds called eezgi look a little like burnt popcorn; dry, they last for months stored in cloth bags. Carefully packed in a sheep-stomach wrapper, the buttery clotted cream known as urum—made from fat-rich yak or sheep milk—will warm bellies all through the winter, when temperatures regularly drop well below zero.

Warinner’s personal favorite? The “mash” left behind when turning cow or yak milk into an alcoholic drink called shimin arkhi. “At the bottom of the still, you have an oily yogurt that’s delicious,” she says.

Her long trip to Khatgal wasn’t about culinary curiosity, however. Warinner was there to solve a mystery: Despite the dairy diversity she saw, an estimated 95 percent of Mongolians are, genetically speaking, lactose intolerant. Yet, in the frost-free summer months, she believes they may be getting up to half their calories from milk products.

Scientists once thought dairying and the ability to drink milk went hand in hand. What she found in Mongolia has pushed Warinner to posit a new explanation. On her visit to Khatgal, she says, the answer was all around her, even if she couldn’t see it.

Sitting, transfixed, in homes made from wool, leather, and wood, she was struck by the contrast with the plastic and steel kitchens she was familiar with in the US and Europe. Mongolians are surrounded by microscopic organisms: the bacteria that ferment the milk into their assorted foodstuffs, the microbes in their guts and on the dairy-soaked felt of their yurts. The way these invisible creatures interact with each other, with the environment, and with our bodies creates a dynamic ecosystem.

That’s not unique. Everyone lives with a billions-strong universe of microbes in, on, and around them. Several pounds’ worth thrive in our guts alone. Researchers have dubbed this wee world the microbiome and are just beginning to understand the role it plays in our health.

Some of these colonies, though, are more diverse than others: Warinner is still working on sampling the Khatgal herders’ microbiomes, but another team has already gathered evidence that the Mongolian bacterial makeup differs from those found in more-industrial areas of the world. Charting the ecosystem they are a part of might someday help explain why the population is able to eat so much dairy—​and offer clues to help people everywhere who are lactose intolerant.

Warinner argues that a better understanding of the complex microbial universe inhabiting every Mongolian yurt could also provide insight into a problem that goes far beyond helping folks eat more brie. As communities around the world abandon traditional lifestyles, so-called diseases of civilization, like dementia, diabetes, and food intolerances, are on the rise.

Warinner is convinced that the Mongolian affinity for dairy is made possible by a mastery of bacteria 3,000 years or more in the making. By scraping gunk off the teeth of steppe dwellers who died thousands of years ago, she’s been able to prove that milk has held a prominent place in the Mongolian diet for millennia. Understanding the differences between traditional microbiomes like theirs and those prevalent in the industrialized world could help explain the illnesses that accompany modern lifestyles—and perhaps be the beginning of a different, more beneficial approach to diet and health.

Nowadays, Warinner does her detective work at the Max Planck Institute for the Science of Human History’s ancient DNA lab, situated on the second floor of a high-rise bioscience facility overlooking the historic center of the medieval town of Jena, Germany. To prevent any errant DNA from contaminating its samples, entering the lab involves a half-hour protocol, including disinfection of foreign objects, and putting on head-to-toe Tyvek jumpsuits, surgical face masks, and eye shields. Inside, postdocs and technicians wielding drills and picks harvest fragments of dental plaque from the teeth of people who died long ago. It’s here that many of Warinner’s Mongolian specimens get cataloged, analyzed, and archived.

Her path to the lab began in 2010, when she was a postdoctoral researcher in Switzerland. Warinner was looking for ways to find evidence of infectious disease on centuries-old skeletons. She started with dental caries, or cavities—spots where bacteria had burrowed into the tooth enamel. To get a good look, she spent a lot of time clearing away plaque:​ mineral deposits scientists call “calculus,” and that, in the absence of modern dentistry, accumulate on teeth in an unsightly brown mass.

Around the same time, Amanda Henry, now a researcher at the University of Leiden in the Netherlands, put calculus scraped from Neanderthal teeth under the microscope and spotted starch grains trapped in the mineral layers. The results provided evidence that the population ate a diverse diet that included plants as well as meat.

Hearing about the work, Warinner wondered if looking at specimens from a medieval German cemetery might yield similar insights. But when she checked for food remains under the microscope, masses of perfectly preserved bacteria blocked her from doing so. “They were literally in your way, obscuring your view,” she recalls. The samples were teeming with microbial and human genes, preserved and protected by a hard mineral matrix.

Warinner had discovered a way to see the tiny organisms in the archaeological record, and with them, a means to study diet. “I realized this was a really rich source of bacterial DNA no one had thought of before,” Warinner says. “It’s a time capsule that gives us access to inf