Amid the countless edible plants and animals on Earth, there's little consideration for the ground beneath our feet. Intentionally eating dirt, also called geophagy, is a natural instinct and may serve a greater health purpose.
Some humans' urge to consume clay may stem from the activity's protective properties for the digestive system, according to new research to be published in The Quarterly Review of Biology.
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After examining 482 cases of human geophagy and 330 records of the practice among animals in a meta-analysis, researchers led by Sera Young of Cornell University discovered that eating dirt had little to do with being hungry or seeking minerals the body might be lacking. Rather, the team found that geophagy may help stave off pathogens in the gut, especially for pregnant women and pre-adolescent children.
Previous theories held that geophagy resulted from hunger or even a lack of nutrients such as iron in a person's diet, but neither seems to be the case.
The research revealed the types of clay consumed have little iron, calcium and zinc, rendering them low in nutritional value. In addition, older individuals with calcium deficiencies do not generally practice geophagy, which weakens the theory that people turn to the practice when their bodies need specific minerals.
Pregnant women and children living in tropical regions of the world, the individuals who consume dirt often, are also the most vulnerable to parasites and pathogens. Practicing geophagy makes sense to these groups, especially if they're experiencing acute digestive illness.
In another study by Young, she found little evidence to support the claim that geophagy actually introduced harmful pathogens into the digestive system, despite other research linking the practice to increased illness in some school children.
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True, the team found geophagy to occur most frequently among people experiencing gastrointestinal illnesses, but that doesn't mean eating dirt gave rise to them. Instead of introducing pathogens, geophagy is an effort to allay ones already there, researchers say. Scientists have drawn similar conclusions among non-human primate species as well.
But before giving that mud pie a shot, consider the fact that people who practice geophagy gather dirt from deeper in the ground and frequently boil the stuff before munching on it.