Q&A: Why People Eat Dirt

Would you eat sand, chalk, coffee grounds, or chicken poop? Some people do, and it’s called pica—the craving and purposive consumption of non-food substances. 

Though pregnant women and children are reportedly the most common pica practitioners, scientists haven’t thoroughly documented its prevalence. That’s why a team including Christopher Golden, an eco-epidemiologist and National Geographic Conservation Trust grantee, conducted the first population-based study of pica in Madagascar, where many people are known to practice the behavior.

Weird & Wild recently talked to Golden to get the dirt on pica, as well as a few surprises from his research.

picture of a man preparing "tany manara."
A man in Madagascar prepares "tany manara," a form of white earth often consumed to prevent the onset of future illness. Photographs courtesy Christopher Golden.

Q. How did you get involved in researching pica?

A. I started getting interested in Madagascar when I was 9 and did a report on the ring-tailed lemur. From then on I was completely in love with Madagascar—I’ve now been working there for 13 years. I started off doing work in behavioral ecology and later exploring connections between natural resource use and human health. I’m interested in how [pica] impacts [people’s] health status. Specifically this topic got to be an interest to me [via study co-author Sera Young of Cornell]. She’d done extensive work on pica, but there have never been studies done in Madagascar on this subject.

Why hasn’t there been any studies in Madagascar?

I’m not sure, because it’s incredibly prevalent. Though it’s concealed, it’s not concealed well—you even find soils for sale at the market.

A picture of someone holding "vato malemy"
"Vato malemy," a reddish clod of river sediment thought to cure gastrointestinal illness.

What were the main findings, and how were they surprising?

What we found was that Madagascar was acharacteristic of previous pica studies—the prevalence rates were very high in general across the board. We found high rates within men, and not these peak rates during pregnancy and adolescence. That’s a major charasteristic of pica, you see these peaks during pregnancy and adoloscence, and that gets into the [two main] mechanisms by which pica is explained. [One is that pregnant women and adolescents] crave trace minerals in soil, because nutritional needs during rapid growth and pregnancy peak, and your nutritional needs also increase.

[But] when [scientists have] actually gone to look to see whether that’s physiologically or biologically possible, you can’t derive a lot of bioavailable metals and minerals from soil. It’s still possible people are craving or eating it for this reason even though it may not serve any health purpose. The other mechanism is that specific soils [may be] serving to cleanse and deworm consumers’ intestinal tract. Unlike typical case studies of pica, we didn’t find [peaks in pregnancy and adolescence] in our studies—and high rates of use in men.

A girl holding vato malemy in Madagascar.

What’s your interpretation of the results?

My interpretation is that Madagascar is a unique place where men are participating in pica more than in any other places. My guess, which is not substantiated, is that prior research study designs may have ignored men in their study samples as an artifact of studying pregnant women.

So why were people practicing pica?

My research hasn’t done enough analysis or data-crunching to be able to tackle that. Anecdotally, one major reason why people were eating certain types of soil in the study was [preventative] health benefits or to bring good luck. Further, certain soils were used to treat gastrointestinal illnesses.

Would this be true of people in the industrialized world as well?

You can draw parallels in the U.S. because this behavior is not exclusive to rural populations in developing countries. There are many people who are participating in pica within the U.S.—ie. people that sell [the red] clays in Georgia. A close college friend of mine is a frequent consumer of chalk. It is very prevalent, yet stigmatized and thus underreported.

Is there a story or surprising substance from your field research in Madagascar that our readers might be interested in?

[One of the substances] I didn’t expect was chicken feces. Also, the specificity by which people will select particular substances. Visually the same, but differences apparent to the consumer.

Overall, why is this an important topic of study?

Generally it’s a lot about closing knowledge gaps—before this behavior was underreported in Madagascar, and now we’ve closed that gap. It’s the first study that shows pica being highly prevalent in men, and opens up this whole field of research to [ideally] have fellow researchers acknowledge both men and women in their studies. We may be misunderstanding a lot of evolutionary underpinnings by focusing so exclusively on a target demographic population that we think this is prevalent for, such as pregnancy.

The study appears October 17 in the journal PLoS ONE


Meet the Author
Christine Dell'Amore, environment writer/editor for National Geographic News, has reported from six continents, including Antarctica. She has also written for Smithsonian magazine and the Washington Post. Christine holds a masters degree in journalism with a specialty in environmental reporting from the University of Colorado at Boulder. Her book, South Pole, was published in 2012.