Eating dirt: It’s actually better than you think

Although “eating dirt” is a slur that goes back to the Old Testament, millions of people crave and eat earth, from Georgia to Zanzibar and nearly everywhere in between. It is particularly common during pregnancy.

Hundreds of animal species also seek out and eat earth. In most cases, the earth that is craved is not the dark, humus-rich soil in your garden, but is rather smooth and clay-rich.

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The recent UN-declared World Soil Day paid homage to the importance of soil for our well-being. But when you think of the many ways that soil is integral to life — from food production to soccer fields — eating it to protect against illness is probably is not one of them. 

Many attest they eat dirt not out of desperation, but relish the option, describing it with great pleasure. In 15 years of studying geophagy, I have listened to people on four continents who have told me how their “mouth waters just talking about it.” 

Humans go to great lengths to eat the earth they crave; they pay $20 for a plastic bag  of “white dirt” to be shipped discreetly to their house, walk long distances to the spot with the “good earth,” and hide the practice from their doctors, dentists and friends. Geophagy is trendy, but it sure isn’t new; descriptions of cravings for earth date back 2,000 years.

Animals such as parrots and spider monkeys also go to great lengths to get the earth they crave, risking attack when they descend from the tree canopy or emerge from the jungle to exposed sites of clay.

The craving and consumption of items that aren’t considered food is known as pica (after the magpie, a bird thought to have an indiscriminate appetite). Some pica behaviors, like eating coins or batteries, are associated with serious mental illness and are clearly pathological. But the craving of earth, rarely carries with it the connotations of mental illness, although it can be stigmatizing.

The causes of this more innocuous form of pica, geophagy, have remained an enigma since Hippocrates first documented it. Why do humans and animals take such risks to eat it?

In our recent review of geophagy among 136 species of non-human primates, we found evidence that geophagy could be a very important strategy to adapt to the many and increasing stressors that primates in the wild experience. 

Climate change and increased greenhouse gases — specifically carbon dioxide — are driving declines in the nutritional quality of many plants preferred by primates. We suspect that eating earth is an unappreciated adaptive strategy to overcome this. 

Geophagy makes it possible for primates to eat plants that would otherwise be harmful, as the earth shields them from plant toxins. This can occur when earth binds the offending item before it enters the bloodstream or when it forms a barrier in the gut that prevents pathogens or toxins from passing through. So too does consumption of clay by humans shield us from toxins.

For hundreds of years, it has been thought that earth could be a sort of multivitamin of Mother Nature, that it provided a micronutrient — such as iron — that was otherwise missing from the diet. However, empirical support for this hypothesis is lacking. Soil samples that don’t contain iron are often preferred over samples with iron. In several sets of experiments, we have shown that there is generally minimal iron present that can be absorbed by our bodies.

So, the most promising explanation is a fairly counter-intuitive one: soil is protective. Earth rich in clay can shield us and other animals from harmful bacteria, viruses, or chemicals in food. Think of it as a mud mask for the gut.

Eating earth when we are experiencing nausea or diarrhea (the side effects of exposure to harmful pathogens or toxins), can help us to feel better. In this scenario, it protects us against some of the consequences of toxins or pathogens. The “kao” in the brand name for the anti-diarrheal Kaopectate comes from kaolin, a type of clay.

That so many species, including us humans, go to such lengths to eat earth suggests that there is something to it. This something, this enigma, deserves more attention from both the medical and zoological communities. Understanding the causes and consequences of geophagy could lead to important insights into keeping many humans and animals healthy.

So instead of asking “why on earth,” you may want to reconsider what eating dirt may do for all of us. 

Sera Young is an assistant professor of anthropology and global health at Northwestern University and a Public Voices fellow through The OpEd Project. She received the Margaret Mead Award for her book, Craving Earth. Follow her on Twitter: @profserayoung.