Study: Animals and humans eat clay to rid toxins

June 10, 2011 By Krishna Ramanujan, Cornell University

A woman collects geophagic soil on Pemba Island, Zanzibar, Tanzania. (Sera Young)
(Medical Xpress) -- The phrase "eat dirt" takes on a whole new meaning when used by biologists, who have widely observed that humans, birds and mammals all engage in geophagy. A new Cornell study concludes that in humans, it's best explained as providing protection from dietary chemicals, parasites and pathogens.

So said lead author Sera Young, Ph.D. '08, of the study, published in the June issue of the Quarterly Review of Biology. Young will be a research scientist in nutritional sciences at Cornell beginning July 1 and is the author of "Craving Earth: Understanding Pica -- the Urge to Eat Clay, Starch, Ice and Chalk" (2011).

Reports of human geophagy have puzzled for hundreds of years, said co-author Paul Sherman, Cornell professor of neurobiology and behavior. It has been described in almost every country but most frequently in the tropics.

Other previous explanations for geophagy have included hunger or the need to acquire such nutrients as iron, zinc or calcium.

The researchers analyzed 482 cultural accounts of human geophagy and 330 accounts of geophagy among 297 species of birds, reptiles and , including 70 primate species. Young and colleagues entered details of these accounts into a database and then looked for patterns to evaluate each hypothesis.

They found that people who practice geophagy never claim to do it just to fill an empty stomach; they eat only small amounts and do so even when food is plentiful. Similarly, the researchers found that the type of dirt people eat is rich in clay, which lacks bio-available nutrients, dispelling the idea that geophagy adds nutrients to a person's diet. Data suggest, in fact, that geophagic earth can bind such micronutrients as iron and zinc, which may explain the strong association between geophagy and anemia.

The researchers found that geophagy occurred most often among pregnant women and children in where thrive. It was also associated with the of toxic substances and gastrointestinal distress. In pregnant women, immune systems are adaptively turned down so as not to reject the fetus, but at the same time, food-borne pathogens can be harmful to the health of both mother and fetus, said Sherman.

"Geophagy is most common in the first trimester of pregnancy, the time when the embryo is most vulnerable," Sherman said. Similarly, children and adolescents are highly susceptible to toxins, which may explain why they also practice geophagy, he said.

People who eat dirt search out specific soils they consider to be clean and safe. The dirt is also typically carefully prepared and even heated before ingesting.

While this is the most comprehensive study examining geophagy in humans, according to the authors, previous animal research has shown that poisoned rats will eat clay when offered a variety of substances, and researchers also have documented that various primates including chimpanzees and such birds as parrots ingest clay soil after eating toxic fruits or experiencing gastrointestinal distress.

"In most of the places where people eat earth, they don't have as much access to medical treatment, and geophagy has been practiced long before modern medicine," said Sherman. "Geophagy has been something that has been looked down on, but it's not just a mistake -- rather clay is a natural medicament, which acts much like commercial Kaopectate."

Other co-authors include Cornell researchers Julius Lucks, who will start July 1 as an assistant professor of chemical and biomolecular engineering, and Gretel Pelto, a visiting nutritional scientist. The study was funded by the Hertz Foundation, National Institutes of Health, Wenner-Gren Foundation and the Stephen H. Weiss Presidential Fellowship fund at Cornell.

Explore further: Eating dirt can be good for the belly, researchers find

Related Stories

Eating dirt can be good for the belly, researchers find

June 2, 2011
Most of us never considered eating the mud pies we made as kids, but for many people all over the world, dining on dirt is nothing out of the ordinary. Now an extensive meta-analysis forthcoming in the June issue of The Quarterly ...

Morning sickness is pregnancy 'wellness insurance'

June 26, 2008
Morning sickness. It's the bane of many of a pregnancy. And many a future mother wonders at the apparently unnecessary suffering.

Morning sickness protects mom and baby

July 13, 2006
A British study says nausea and vomiting caused by "morning sickness" is nature's way of protecting mother and baby from food poisoning.

Explaining chemotherapy-associated nausea

January 30, 2008
A new study from the Monell Center increases understanding of the biological mechanisms responsible for the nausea and vomiting that often afflict patients undergoing chemotherapy. The findings could lead to the development ...

Big, social, Island-dwelling birds live longest

January 13, 2010
( -- Research may help explain underlying evolutionary principles that shape life spans for many organisms, including humans.

Study: Seafood safe and healthy to eat

October 17, 2006
U.S. scientists say people can safely decrease their risk of heart disease by substituting seafood for other animal proteins.

Recommended for you

Gene mutation found to cause macrocephaly and intellectual deficits

November 13, 2018
The absence of one copy of a single gene in the brain causes a rare, as-yet-unnamed neurological disorder, according to new research that builds on decades of work by a University at Buffalo biochemist and his colleagues.

Can scientists change mucus to make it easier to clear, limiting harm to lungs?

November 12, 2018
For healthy people, mucus is our friend. It traps potential pathogens so our airways can dispatch nasty bugs before they cause harm to our lungs. But for people with conditions such as cystic fibrosis (CF) and chronic obstructive ...

Mutations, CRISPR, and the biology behind movement disorders

November 12, 2018
Scientists at the RIKEN Center for Brain Science (CBS) in Japan have discovered how mutations related to a group of movement disorders produce their effects. Published in Proceedings of the National Academy of Sciences, the ...

Researchers explain how your muscles form

November 12, 2018
All vertebrates need muscles to function; they are the most abundant tissue in the human body and are integral to movement.

Salmonella found to be resistant to different classes of antibiotics

November 12, 2018
Brazil's Ministry of Health received reports of 11,524 outbreaks of foodborne diseases between 2000 and 2015, with 219,909 individuals falling sick and 167 dying from such diseases. Bacteria caused most outbreaks of such ...

High fat diet has lasting effects on the liver

November 9, 2018
Consuming a high-fat, high-sugar diet causes a harmful accumulation of fat in the liver that may not reverse even after switching to a healthier diet, according to a new study by scientists from Weill Cornell Medicine and ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.