Posted on 06/02/2011 3:24:23 PM PDT by decimon
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 Review of Biology helps explain why.
According to the research, the most probable explanation for human geophagy—the eating of earth—is that 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, says 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 up to now have been unable to definitively explain why people crave earth. Several hypotheses had been considered plausible. Some researchers think geophagy is simply a consequence of food shortage. In other words, people eat dirt to ease the pangs of hunger, even though it doesn't provide any nutritional value. Others have suggested that nutrition is exactly why dirt is consumed; perhaps people crave dirt because it provides nutrients they lack, such as iron, zinc, or calcium. Still others posit that earth has a protective effect, working as a shield against ingested parasites, pathogens, and plant toxins.
To sort through the possible explanations, 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. The researchers could then use patterns in the data to evaluate each potential explanation.
They found the hunger hypothesis unlikely. Studies in the database indicate that geophagy is common even when food is plentiful. Moreover, when people eat dirt they tend to eat only small quantities that are unlikely to fill an empty stomach.
The nutrition hypothesis was also a poor fit to the data. The database shows that the kind of earth people eat most often is a type of clay that contains low amounts of nutrients like iron, zinc, and calcium. Plus, if calcium deficiency drove people to eat dirt, one would expect them to do it most often at life stages when they need calcium the most—adolescence or old age. But that isn't the case, according to the database. Reports do indicate that geophagy is often associated with anemia, but several studies have shown that cravings for earth continue even after people are given iron supplements. What's more, some research suggests that clay can bind to nutrients in the stomach, making them hard to digest. If that's true, it's not a lack of nutrients that causes geophagy; rather it could be the other way around.
Overall, the protection hypothesis fits the data best, the Cornell researchers found. 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. It's unlikely the intestinal problems are caused by the dirt itself because the type of clay people usually eat comes from deep in the ground, where pathogens and parasites are unlikely to contaminate it. Plus, people usually boil the clay before eating it.
More study would be helpful to confirm the protection hypothesis, the researchers say, but the available data at this point clearly support it over the other explanations.
"We hope this paper stimulates [more] research," Young and her colleagues write. "More importantly, we hope readers agree that it is time to stop regarding geophagy as a bizarre, non-adaptive gustatory mistake."
"With these data, it is clear that geophagy is a widespread behavior in humans … that occurs during both vulnerable life stages and when facing ecological conditions that require protection."
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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).
Young has also released a book on the subject called Craving Earth: Understanding Pica—the Urge to Eat Clay, Starch, Ice, and Chalk.
The premier review journal in biology since 1926, The Quarterly Review of Biology publishes articles in all areas of biology but with a traditional emphasis on evolution, ecology, and organismal biology. QRB papers do not merely summarize a topic, but offer important new ideas, concepts, and syntheses. They often shape the course of future research within a field. In addition, the book review section of the QRB is the most comprehensive in biology.
University of Chicago Press Journal ... I’m surprised they’re not advising us to eat something else.
In the movie “And Then There Were None” based on the Agatha Christie story, the butler says that just before they serve a roast that was dropped on the floor. “Everybody has to eat a pound of dirt before they die”.
Does making out in the sand at the beach count at midnight? That sand was pretty good!
Years ago, there was a show about immunology on PBS.
One of the things they talked about was a group of hippy-types living in a commune in Va, I think.
Most of what they ate they grew themselves.
Once a week, they actually took some of the local garden dirt and sprinkled it on their salads.
And according to the reports, these people NEVER got sick. Never.
Problem is, I know enough about botany and biology and local fauna that I realize you could probably do this 100 times and be totally fine.
The 101st time you try it, you pick up some cootie that basically starts digesting YOU from the inside out!
LOLOLOLOL!
My mother in law often said “eat a peck of dirt before you die”. What a character she was. She was also an ardent fan of Reagan.
IIRC penicillin was discovered when Fleming had accidentally let some petri dishes get contaminated, and he didn’t realize it until he put them under the scope.
A worldwide search was then started to find related species of penicillium that had higher production rates.
After searching wordwide, nobody found anything, and one of the scientists conducting the search spotted an orange at a market right near the clinic that had a bit of blue mold on it so he said What the hey! and bought it, JACKPOT!!
The subspecies that they use today produce literally many thousands of times more that the original.
Interesting factoid: the penicillium that makes penicillin is closely related to another species of the penicillin bacteria that is the stuff that makes blue cheese blue!
There have been rare cases of people allergic to penicillin going into shock after exposure to blue cheese.
Like I always say (I really do):
GOD MADE DIRT, DIRT DON’T HURT!
I suspect that peoples who eat dirt know which dirt to eat and possibly prepare it somehow.
Just like most plants, which are somewhat edible. But many have alkaloids in them that will make you hurl.
But I have two plants that grow in my yard (right next to my garden!) that if you even took a few leaves, chewed them up and spit them out, you’d be dead before nightfall.
Foxglove and hemlock.
Hemlock is particularly bad because it has a very herbal smell to it. An immigrant gal from SE Asia living in Tacoma died from it last summer because she mixed it in her salad or soup, can’t remember which.
I recall someone telling me about a book written regarding how women ate certain types of dirt down south during the Civil War or something along those lines.
Correct. But they’re not protozoa and they’re not viruses so I tend to lump them together. But that’s OK, cause I’m not a microbiologist...
;-)
I am absolutely convinced we are too clean and too sterile. I am convinced that a little dirt and grime and junk is good for both kids and adults. I don’t mean live with rotting food and germs and diseased people. But we live in such sterile cleanliness from the cradle, I really wonder if things like Asthma and Autism adn some allergies come from the body not having to build up defense early enough, or being tested often enough. What doesn’t kill you makes you stronger, etc.
I’m convinced. I think a little cigarette smoke is good for you now and then. I said, a little.
I remember when that group of 8th graders knocked me down and made me eat dirt. That’s when I gave up teaching. Didn’t get sick, though.
Yeah, I guess that would be...disconcerting.
Dang, someone already got to the North Korean jokes.
Okay...
The drawback to eating dirt...
...if you soil yourself, it’s with actual soil.
I had one of those herbs and roots kind of grandmothers in Kentucky who used to advise that a pound of dirt a year was good for you.
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