" " Geophagic earth collected from a rain forest on Pemba Island, Zanzibar. Both humans and animals seek out this earth to eat. Sera Lewise Young

In gas stations and flea markets all around the southeastern United States, you can find a cardboard box full of blocks of white clay. They're unmarked, but the people looking for them know what they're for. In Kenya, you can buy reddish dirt on the street, formed into little pellets that look like baby carrots. In Uganda, you can buy "Yankee Doodle" brand dirt at the grocery store. A website called Earth's Clay Store sells clays from all over the world and ships them right to your home. But what are you supposed to do with it when it gets to you?

Well, you eat it.



Pica

You might have a vague sense that you've heard of people eating dirt before — pregnant women, maybe? Pica is the overarching term for craving and eating things that aren't food. In the 6th century, a physician named Aëtius of Amida noticed people sticking non-food items in their mouths, the way magpies (pica, in Latin) pick up random objects in their beaks. He figured these people had entirely indiscriminate appetites for just any old thing and termed the behavior after the magpie.

It turns out, pica is kind of a misnomer, because pica cravings are actually very specific, but according to the Diagnostic and Statistical Manual of Mental Disorders (DSM), it includes a range of behaviors. Some people crave paperclips, batteries or coins — these cravings are considered by the DSM to be on the spectrum of obsessive-compulsive disorder, schizophrenia, clear mental illnesses — but pica can also include cravings for raw starch (amylophagy), ice (pagophagy) and dirt (geophagy).

" " Geophagic earth is collected from the wild, sold in open-air markets and even in grocery stores throughout East Africa. Sera Lewise Young

Geophagy is one form of pica found in almost every country in the world.

"I was surprised when I first saw it," says Sera Young, assistant professor in the Department of Anthropology at Northwestern University. "I was studying pregnant women ethnography in Zanzibar, and I asked a woman what she ate when she's pregnant, and in Swahili she said, 'Every day I take earth from this wall and eat it.' I was just learning Swahili and was pretty good at it, but I really didn't think I was understanding correctly. My research assistant was like, 'Yeah, you heard right!'"

Young ended up writing her Ph.D. dissertation on geophagy, and winning the Margaret Mead Award in 2013 for her book "Craving Earth" which detailed her research about geophagy practices worldwide. In her research, Young tracked down medical literature; historical texts; research on animal behavior, soil science and parasitology, and came to the conclusion that there are four explanations as to why people eat dirt.



1. It's Aberrant Behavior

The most common and longest-running conventional wisdom about geophagy is that there is no good reason for it — it's a pathology, it's aberrant behavior of some unknown origin.

"It's the 'women, they know not what they do' explanation," says Young. "It was basically white men writing about this for the past few hundred years, and it was dismissed as aberrant. It's true, it is often women, and most often pregnant women who especially don't know what they're doing. And it's most common around the equator, in the tropics, so of course brown people definitely don't know what they're doing. We can refute this — there are so many species of animals that go to great risk to get clay and charcoal, like the colobus monkey that steals charcoal from villagers."

But even so, we know very little about geophagy because for centuries scientists were stubbornly lacking curiosity about it.



2. Dirt Is Mother Nature's Multivitamin

The first explanation scientists have come up with to explain why hundreds of thousands of people worldwide crave and eat dirt is that there must be something useful in the clay — micronutrients of some kind.

"The Mother Nature's multivitamin explanation is a really intuitive one," says Young.

But no dice. For starters, although the clay her study participants in Zanzibar were eating was tinged with red, indicating iron content, investigations into whether that iron could be absorbed and used by the body came up empty. Plus, according to Young, people generally prefer whiter clay: If you gave a geophagist the option of snacking on Georgia white kaolin or the reddish clay found on Zanzibar, they'll almost always pick the white kaolin, which does not contain iron.



3. Dirt Provides Protection from Germs

The explanation that eating dirt is somehow protective doesn't make much intuitive sense — after all, we're supposed to stay away from dirt, wash our hands, clean our clothes, take off our shoes when we enter the house. If you'll recall from the last time you read the Bible, even the snake had to eat the dust as punishment for talking Eve into eating the forbidden apple.

But clay face masks suck the impurities from your skin, and they're made of dirt, right? According to Young, eating clay might coat the inside of the gut, in much the same way a mud mask coats the face. But why would somebody need an intestine mud mask? The answer is, protection from pathogens and harmful chemicals.

Most toxins enter your body in the things you eat. You digest the food and it's absorbed through the wall of your intestine and into your bloodstream — lots of pathogens and chemicals get to us in this way, too. Clays can bind to the mucin (mucus) layer inside your gut, forming a barrier.

"In rabbits, clay has been shown to stimulate the production of mucin, creating a barrier to potential harmful pathogens or chemicals getting into your bloodstream," says Young. "It can also bind with whatever harmful thing you're eating. For example, in the Andes, people eat wild potatoes which contain these toxic chemicals called glycoalkaloids. But after they dip the potatoes in clay, they become safe to eat."

But while eating clay might protect from pathogens and harmful chemicals, which is especially important for pregnant women, there's something of a Goldilocks Principle at play here: you want to shield yourself from the harmful stuff, but you also don't want to protect yourself from the nutrients you need. For example, if you eat a steak that's full of both bioavailable iron and pathogens, but you eat clay at the same time, the iron will become bound by the clay, and won't be absorbed by your gut. Although the clay might be protecting you from pathogens to some extent, it's also preventing you from absorbing the nutrients.



4. Dirt Makes Your Tummy Feel Better

The third explanation for why people eat dirt or clay is that it might help with nausea, vomiting and diarrhea by coating the stomach. After all, a number of anti-diarrheal treatments have kaolin in them. Kaolin puts the puts the Kao- in Kaopectate!



How Cravings Start

Though the reasons for geophagy are still rather mysterious, the question remains: How do people find out they have a craving for dirt in the first place?

"There are instances of people having these cravings de novo — without having tried it before," says Young. "But the fact is, if you grow up seeing your mom sending your dad to go get this exact dirt, or see your aunties are eating dirt, you see it in the stores for sale, you're much more likely to engage in it."

But Young also stresses that geophagy is far more common than we realize — although it's perceived as an exotic behavior that happens in far-away places, people are eating clay all the time in the U.S.

"People don't like to talk about it or admit it. When I'm doing ethnographic interviews, I always ask 'how much earth do you eat?' instead of 'do you eat earth?', because so many people have sworn they don't eat it, and later tell me they do but they lied because 'I didn't want you to think I was poor.'"