Don't eat dirt

Don't eat dirt. It's bad for you.

This might seem like a head-slappingly obvious piece of advice, but there have been a slew of reports in recent years suggesting just the opposite.  Here are a few headlines:

• "Eating Dirt: The benefits of being (relatively) filthy" in Scientific American
• "Eating Dirt: It might be good for you" from the ABC News website
• "Eating dirt can be good for the belly, researchers find" from Science Daily, summarizing a 2011 anthropological study in the Quarterly Review of Biology
• "The old and mysterious practice of eating dirt, revealed" at NPR.org, describing a documentary film, Eat White Dirt, released last year.

And there's even a blogger who claims that dirt is "the missing superfood."

These articles describe a custom in which women, especially pregnant women are advised to eat dirt or clay, which some people claim offers health benefits. The ABC News story quotes a Georgia woman saying about the clay she eats, "The good stuff is real smooth. It's just like a piece of candy."

There's even a name for this practice: geophagy, or "earth eating." The NPR story claims this practice goes back millenia. Of course, ancient humans tended to die before they reached the age of 40, so I'm not sure I want to imitate their dietary practices.

Dirt is not the new superfood. Quite the contrary: dirt is the home of some nasty parasites, including a type of worm call toxocara, which can make you extremely ill. These worms are invisible to the naked eye–you can't see them crawling around–but they can cause devastating disease and even death.

This came to my attention last week in a case report in the New England Journal of Medicine (written by Dr. Steven Feske and colleagues) about a 38-year-old pregnant woman who was admitted to Massachusetts General Hospital with back and neck pain, vomiting, and headache. She was initially treated and released, but 11 days later,

"...she began to hyperventilate and her vision went black from the periphery to the center. The symptoms lasted for approximately 2 minutes and were followed by spots in her visual fields, headache, neck pain that radiated to her arms, nausea, and dizziness."

Mass General ran extensive tests, and her brain MRI showed lesions "suggestive of multiple strokes." Given all her symptoms, her physicians suspected that she was infected by a parasitic worm (a helminth or nematode) caused by eating dirt or clay. The patient was originally from Guatemala, where nematode infections are common, and where dirt-eating during pregnancy is encouraged in some areas. As they explain in the NEJM article:

“According to a tourist brochure from the Christian shrine in Esquipulas, Guatemala, 'In Guatemala, eating clay tablets combines healing, devotional reminders, blessings from Our Lord of Esquipulas, good fortune, and pregnancy nutrition.' ” 

Some of the tests came back positive for Toxocara, a parasite roundworm. Only then did the patient reveal that she had been eating dirt, but not from Guatemala, which she had not visited in several years. She had eaten dirt from a neighbor's yard in Massachusetts.

Fortunately, there is an effective treatment for Toxocara infection, and the patient recovered and delivered a healthy baby.

The roundworms that cause toxocariasis are commonly found in dirt in the U.S. They are transmitted by dogs, who spread them around through their feces. Pretty disgusting, right? A variety of other nasty parasites are transmitted through soil, including other kinds of roundworms, whipworms, and hookworms.

So don't eat dirt. It's not good for you. Really.