The practice of dirt-eating, or geophagy, is common, perhaps because "clean" dirt appears to impart some protection against parasites and pathogens.
There’s a habit that’s had scientists puzzled: the practice of geophagy—eating dirt. People around the world munch on dirt, and not just when they’re hungry enough to eat anything. So is there any nutritional or health benefit? A meta-analysis published in the Quarterly Review of Biology may offer a clue.
Researchers collected more than 480 reports from missionaries, plantation doctors, explorers and anthropologists. These included who was eating dirt and under what circumstances. Seems that dirt doesn’t offer much in the way of nutrition—but it may protect against toxins, pathogens and parasites.
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Journal Paper: Sera L. Young, Paul W. Sherman, Julius Beau Lucks, Gretel H. Pelto, "Why on Earth?: Evaluating Hypotheses about the Physiological Functions of Human Geophagy." The Quarterly Review of Biology 86:2 (June 2011).