Turns out those kids making mud pies in the backyard might be onto something. After deliberating three hypothesizes for why people compulsively eat earth (known as geophagy), researchers have narrowed it down to one: eating earth may protect the stomach against toxins, parasites, and pathogens Why on Earth?: Evaluating Hypotheses about the Physiological Functions of Human Geophagy. Sera L. Young, Paul W. Sherman, Julius Beau Lucks, and Gretel H. Pelto. The Quarterly Review of Biology, 2011; 86: 2.

Wanna Get Dirrty – Analysis

Geophagy (not to be confused with a name for a middle school course) is one of the most common forms of pica, the compulsive intake of non-nutritious substances such as earth, clay, chalk, soap, and ice. Dating back to ancient Greece– almost 2,000 years ago– geophagy has been reported on every inhabited continent and almost in every country Pica during pregnancy: a frequently underestimated problem. López, LB., Ortega Soler, CR., de Portela, ML. Escuela de Nutrición, Facultad de Medicina, Universidad de Buenos Aires. Archivos Latinoamericanos de Nutrición 2004 Mar;54(1):17-24..

In this most recent study, researchers analyzed 480 cultural accounts of geophagy, which included the circumstances under which earth was consumed and by whom. Researchers initially suspected food shortages played a part, but they found geophagy was common even when food was readily available. Plus, people ate dirt in such small quantities, it would unlikely fill an empty stomach Why on Earth?: Evaluating Hypotheses about the Physiological Functions of Human Geophagy. Sera L. Young, Paul W. Sherman, Julius Beau Lucks, and Gretel H. Pelto. The Quarterly Review of Biology, 2011; 86: 2.

Another proposal suggested people crave dirt because it supplies nutrients they lack such as iron, zinc, or calcium; however the type of earth people ate most is a kind of clay lacking these nutrients. The association between geophagy and anemia didn’t pan out either since people’s craving for earth continued after taking iron supplements Why on Earth?: Evaluating Hypotheses about the Physiological Functions of Human Geophagy. Sera L. Young, Paul W. Sherman, Julius Beau Lucks, and Gretel H. Pelto. The Quarterly Review of Biology, 2011; 86: 2. Some research even suggests clay can bind to nutrients in the stomach, making them difficult for the body to absorb and digest Pica in pregnancy: new ideas about an old condition. Young, SL. Department of Pediatrics, University of California, Davis, California. Annual Review of Nutrition 2010 Aug 21;30:403-22..

The study’s results pointed most directly to the protection hypothesis: earth works as a shield against ingested parasites, pathogens, and plant toxins. Basically, instead of considering a mud mask for the face, maybe it's time to try one for the stomach! Believe it or not, geophagy is most commonly documented in pre-adolescent children and women in their early stages of pregnancy... and both are especially sensitive to parasites and pathogens. In addition, people often eat earth during times of gastrointestinal stress and in tropical climates, where microbes flourish Why on Earth?: Evaluating Hypotheses about the Physiological Functions of Human Geophagy. Sera L. Young, Paul W. Sherman, Julius Beau Lucks, and Gretel H. Pelto. The Quarterly Review of Biology, 2011; 86: 2.

Before grabbing a handful of dirt to ease tummy troubles, keep in mind all earth is not created equal. People most often eat a type of clay found deep in the ground– uncontaminated by pathogens and parasites– and most usually boil the clay before eating it.

TLDR

Eating earth may protect the stomach against toxins, parasites, and pathogens

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