The habit of eating clay, mud or dirt is known as geophagy. Some experts lump it into the same category as pica, which is the abnormal urge to eat coins, paint, soap or other non-food items.

Cultures worldwide have practiced geophagy for centuries, from the ancient Greeks to Native Americans. In most places the habit is limited to women, especially women who are pregnant or of child-bearing age.

The practice is common in sub-Saharan Africa, and many anthropologists believe geophagy was brought to the United States by African slaves. It is now most commonly found among African-American women in the rural South.

Though the practice is rarely if ever recommended by medical professionals, some nutritionists now admit the habit of eating clay may have some real health benefits.

"It is possible that the binding effect of clay would cause it to absorb toxins," said Dr. David L. Katz, nutrition expert at the Yale School of Medicine and a medical contributor for ABC News.