Erik Eckholm reports in the New York Times
"Clay Eating Proves Widespread But Reason Is Uncertain," on 22 July 1986:
The practice of eating dirt, usually fine clays, is so common in so many societies that it must be regarded as a normal human behavior rather than an oddity, according to scientists who are studying it. Yet why hundreds of millions of people and dozens of animal species consume earth remains a mystery, and information about the health effects is contradictory and incomplete.
Some evidence indicates that consumption of soils, a practice known as geophagy, can supply minerals otherwise deficient in local diets, fight nausea, indigestion and diarrhea, and even counter ingested poisons. One anthropologist makes a strong case that, by neutralizing the toxic chemicals in wild tubers in the Andes of South America, dietary clays permitted the consumption and later domestication of the potato, now one of the world's main foods.
But medical experts warn that some varieties of clays being consumed can induce dangerous nutritional deficiencies, and physicians have identified a ''geophagic syndrome'' among practitioners in the Middle East who suffered serious ailments following heavy, chronic clay consumption.
The eating of clays occurs among cultural groups on every inhabited continent, observes Donald E. Vermeer, an geographer at Louisiana State University, placing it ''in the normal range of human behavior.'' Often the clay is prepared as a standardized product - shaped or pounded into nuggets and in some cases cooked. In West Africa, a favored variety is smoked and traded more than a thousand miles.
Geophagy is prevalent in Asia, the Middle East, parts of Latin America and in the rural South of the United States. In Sub-Saharan Africa hundreds of cultures including both farmers and nomads consume dirt, mainly clay but in some cases sand, Dr. Vermeer said.
Historical records of earth-eating in Europe go back to 300 B.C., when Aristotle described it, notes Darla E. Danford, a nutritional specialist at the National Research Council. Since then it has been documented ''in both sexes, in all races, and in animals as well as humans,'' and ''in all socioeconomic groups,'' she said. Over the centuries, clay was often prescribed to counter illnesses and poisons, and in some countries it has been mixed into bread dough.
Clay consumption is nearly everywhere most common among pregnant women, perhaps because of its antinausea effects, experts hypothesize. The limited data indicate that from 30 percent to 50 percent of pregnant women in large areas of Africa and among rural blacks in parts of the American South consume clay, according to Dr. Vermeer, and that hundreds of millions of women worldwide do it during pregnancy.
Africans captured in the slave trade brought the habit to the United States with them, which presumably explains its traditional prevalence among blacks. While modernization has probably led to less clay eating in the South in recent decades, Dr. Vermeer said, to some degree the practice seems to have ''gone underground'' because of the stigma many Americans attach to it.
To this day, many rural Southern blacks dig clays with the desired sour taste from local pits, often from subsoil in roadbanks, Dr. Vermeer said. ''In Alabama, damage to roadbanks in some places has been so extensive that the highway department has posted signs requesting local residents not to dig into them,'' he noted.
The clay is baked and often mixed with vinegar and salt. In northern cities, some women who crave clay have their favorite types sent by Southern relatives, while others consume Argo starch, which has similar properties, as a substitute.
Some poor whites in the South also eat clay despite strong social pressures not to. Although American physicians tend instinctively to condemn the practice, ''no current evidence indicates that normal consumption of clays in the American South is either beneficial or harmful,'' Dr. Vermeer said. Eating of excessive quantities can cause intestinal blockage.
Much more research is needed on the incidence and health effects of geophagy, experts in medicine, anthropology and animal physiology asserted recently at a symposium at the annual meeting in Philadelphia of the American Association for the Advancement of Science. One of the few certainties is that the chemical properties of soils eaten around the world differ greatly, making it unlikely that there is any single explanation of why people eat earth or how it affects them.
Although the few available studies usually attribute the practice to women and small children, the incidence among adult men may be under-reported, according to Dr. Danford, who has found in studies of institutionalized, mentally handicapped individuals that many men consume dirt.
Elks and bears, raccoons and parrots, giraffes and zebras are among the many animals that have been spotted eating earth. In Kenya some elephants make perilous nocturnal climbs to hillside caves in search of their favorite dirt. Like people, animals tend to choose subsoils, usually claylike but sometimes sandy, according to Bernadette M. Marriott, a researcher in comparative medicine at the University of Puerto Rico. Sheep in New Zealand annually consume hundreds of pounds each, and agricultural scientists have debated whether to add soil to the rations of intensively produced livestock.
Some studies indicate that by eating dirt, animals are correcting dietary mineral imbalances. Dr. Marriott's research on monkeys in Puerto Rico and Nepal, for example, indicates that the animals are deriving a significant share of the iron they need from clay soils, which they consume from specific sites to which they return over and over. Possibly, she said, the monkeys also ingest bacteria in the soil that provide antibiotic or other pharmaceutical effects.
Rats eat clay to offset ingested poisons, according to Denis Mitchell of the University of Southern California. Rats, which are relatively indiscriminate eaters, often swallow toxic materials ranging from natural chemicals to pesticides.
In experiments, rats fed compounds that caused them stomachaches and diarrhea ate much more clay than normal. The fine clay particles may help prevent intestinal absorption of toxic materials or promote the body's excretion of them, Dr. Mitchell said, an important aid since rats do not vomit when they eat poisons.
Nearly all of the 160 wild potato species growing in the Andes contain toxic chemicals, and so do two of the eight species cultivated and consumed by local Indians. The Indians prevent these tubers from causing gastrointestinal distress either by leaching out the chemicals or by eating the tubers with a dip made of clay and a mustardlike herb, reported Timothy Johns, an anthropologist at the University of California at Berkeley. Some local clays, which are sold in mountain markets, are especially good at chemically countering the poisons - at ''getting rid of the bitter taste,'' as the Indians describe it.
Dr. Johns says this may explain how ancient Andeans were able to begin consuming toxic wild potatoes and eventually domesticate many milder varieties.
Indians in the American Southwest likewise use clay as a condiment with toxic wild tubers, and hunter-gatherer peoples have been observed eating clay with acorns for the same reason. Lurid accounts of famine victims in China or medieval Europe who were reduced to eating dirt may not reflect hunger, as horrified observers imagined, but the need to eat clay as famine victims turned to toxic wild foods, Dr. Johns hypothesized.
The clays consumed by one Nigerian tribe are rich in calcium, contributing to infant development, Dr. Vermeer reported. Another type of West African clay that is widely mined and traded is high in kaolin, which, like the commercial product Kaopectate that contains it, functions as an antidiarrheal.
Despite these many possible medical benefits, experts warn against the attractive assumption that clay eating necessarily represents an instinctive effort to meet nutritional or other medical needs. They point to well-documented hazards. Some kinds of clay are known to bind chemically with iron, zinc and other minerals, preventing their absorption by the body, and clay eating has been periodically associated with anemia for hundreds of years. It is probably this binding power, Dr. Danford observed, that accounts for clay's ancient popularity as a poison antidote.
Extreme overindulgence in clay eating can block the colon, which can lead to perforation of the colon and death. A more common problem is the geophagic syndrome seen over the last three decades among scores of clay eaters in Portugal, Iran, Turkey, Egypt and other Middle Eastern countries. The syndrome involves anemia and zinc deficiencies, growth retardation, delayed sexual maturity, and liver and spleen enlargement, Dr. Danford said.
The victims included both men and women, some of whom ate several cups of clay a day. But this threat may be limited; a study found that clay from Turkey had a higher capacity to bind iron and zinc than clay samples from New Mexico and Georgia.
Dr. Danford warned that dirt eaters anywhere should receive careful medical evaluation, especially pregnant women and children, who could be disastrously affected.
But Dr. Vermeer observed that in many cultures with long histories of dirt eating no ill effects have been documented and in some cases there appear to be benefits. He said he disagreed with the common assumption of physicians that the practice should be stamped out.
Calling above all for more research, the experts agreed with Dr. Danford's statement that the practice of dirt-eating remains ''full of paradoxes.'' (source: The New York Time
s, 22 July 1986)