A new study has provided the most probable explanation for human geophagy — the eating of earth — it protects the stomach against toxins, parasites, and pathogens.
The first written account of human geophagy comes from Hippocrates more than 2,000 years ago, said Sera Young, a researcher at Cornell University and the study's lead author.
Since then, the eating of earth has been reported on every inhabited continent and in almost every country. Despite its ubiquity, scientists until now have been unable to definitively explain why people crave earth. Several hypotheses had been considered plausible.
Some researchers have hypothesized that earth has a protective effect, working as a shield against ingested parasites, pathogens, and plant toxins.
In the study, Young and her colleagues analyzed reports from missionaries, plantation doctors, explorers, and anthropologists to put together a database of more than 480 cultural accounts of geophagy.
The database includes as many details as possible about the circumstances under which earth was consumed, and by whom. Overall, the Cornell researchers found the protection hypothesis to fit the data best.
The database shows that geophagy is documented most commonly in women in the early stages of pregnancy and in pre-adolescent children.
Both categories of people are especially sensitive to parasites and pathogens, according to Young and her colleagues. In addition, geophagy is most common in tropical climates where foodborne microbes are abundant.
Finally, the database shows that people often eat earth during episodes of gastrointestinal stress.
More study would be helpful to confirm the protection hypothesis but the available data at this point clearly support it over the other explanations, the researchers said.
The study will be published in the June issue of The Quarterly Review of Biology.