In order to test this hypothesis, Dr. John Hunter, a geologist at Michigan State University, compared the typical daily consumption of clays in Africa to the suggested dosage of several mineral supplements sold in the U.S. Testing both the mineral content and bioavailability of various clays sold for consumption in the markets of Ghana, Dr. Hunter determined that the clays compared favorably in magnesium, potassium, copper and zinc. The bioavailability of calcium in eaten clays reached 4% of U.S. Recommended Daily Allowance, with iron supplementation reaching as high as 66% of RDA.
These conclusions are especially significant as calcium intake is typically low among African populations that eat clay, and iron deficiency affects as much as 80% of the populace, made more severe by parasitic infection. According to Dr. Hunter, “These levels of mineral-nutrient supplementation point clearly to the practical value of clay eating. Normal dietary intake usually meets daily needs, and clay eating plays a supplementary role.”
A similar study simulated human digestion in the laboratory in order to determine the availability of nutrients in holy clay tablets regularly consumed in by pregnant mothers in Central American Belize. The study, published in The Geographical Review, found that pregnant women eating clay from these tablets could supply nearly 20% of the U.S. RDA for iron and calcium, and significant amounts of magnesium, copper and zinc.
The nutrition hypothesis continues to be studied. While some scientists believe iron-deficient anemia may cause a craving to eat earth, some believe it may actually be caused by eating excessive clay. Others note that, given the diversity of the cultures that historically have used dietary clays and the diverse nature of the clays themselves, it is likely that not all clays are ideal for the same set of uses or conditions, and equally likely that the ingestion of clay does not necessarily serve a single purpose.
Though the study of clay consumption has revealed the potential for digestive and nutritional benefits, scientists believe the most conclusive evidence points to detoxification as a primary benefit of clay eating throughout human history. Its use appears to be one borrowed from and shared by numerous animal species, attesting to
One example from the animal kingdom is the use of clays by animal species that regularly scavenge for a wide variety of foods, often of varying toxicity. Researchers discovered that the ingestion of clays by such species, among them birds, parrots, rats and primates, enables a diverse diet without suffering the toxic effects of substances consumed. The chemical structure of earthen clays determines their suitability as a detoxicant.
Their crystalline shape includes hexagonal networks of silicon-oxygen tetrahedrons, giving them a large surface area with which to bond with potential toxins. In addition, hydroxyl ions and colloidal properties within their structure promote the ability to bind and exchange metals as well as adsorb water and other organic compounds. In cultures across continents, anthropologists and mineralogists have documented and substantiated the use of clays to reduce bioavailability of plant toxins from foods and make them more edible.
These practices are known to have been used by native cultures in present-day Bolivia, Peru and Arizona to eliminate the bitterness of wild potatoes and prevent stomach pains and vomiting, evidenced in the laboratory by the clay's ability to adsorb glycoalkaloids found in the potato species.
Also documented is the practice of baking clay with acorn flour in breads, used historically among peoples of present-day California, Sardinia and Sweden. In examining the mineralogy of the acorn bread clays, a study published in the American Journal of Clinical Nutrition supports the effectiveness of clays both as adsorbers of toxins and as contributors of trace minerals to the diet. Their function was found to reduce the toxicity of acorns by as much as 77%, and to potentially provide 38% of the adult RDA of Calcium.
Similarly, laboratory researchers at the University of Chicago Department of Ecology and Evolution recently demonstrated the ability of kaolin clay to adsorb three commonly ingested chemical toxins using a sophisticated technique modeling the human digestive system. Clay was found to adsorb and thus reduce the toxicity of tannic acid and quinine by 20-30%. Researchers noted that in a true human system the effect could be even greater due to clay’s ability to slow the movement of the digestive process, allowing greater absorption of nutrients and greater adsorption of toxins.
The study of clay eating by anthropologists, geologists, nutritionists and ecologists has in the end come full circle to teach us what we least expected to discover. Historians have long placed the origins of medicine among the Greeks, with Pasteur’s breakthroughs and the development of germ theory playing an equally important role in shaping medicine as we know it today. It seems that this vantage point is exactly what caused our cultural inability to understand the true message behind the clay eater’s practice.
Puzzling over “why people eat dirt,” we labeled earth and clay as non-food substances, but we failed to see the link between clay and our own culturally sanctioned and regularly consumed non-food – conventional pharmaceuticals. We failed to understand that the internal use of clay functions as perhaps the very first medicine practiced by humans, because it seemed outside the realm of possibility that medicine could have been intelligently practiced in pre-historic times.
But good science is particularly adept at shifting paradigms when it encounters them. Timothy Johns of the McGill University School of Dietetics and Human Nutrition has published several papers examining the evolution of early medicine. He defines medicine as the learned behavior of ingesting substances to alleviate distress or maintain health. He and other researchers have placed the earliest examples of these behaviors clearly among higher primates, such as apes and chimpanzees, who consume minerals and forage for plants to perform non-nutritive therapeutic functions.
These behaviors are learned and passed to offspring, and, scientists theorize, were ultimately passed on to early man. One such example was observed and successfully analyzed by Sabrina Krief and researchers at the National Museum of Natural History in Paris. Chimpanzees were found to deliberately ingest a clay as well as leaves from a certain local tree. When analyzed under simulated digestion in the laboratory, it was found that the action of the clay developed clear anti-malarial properties in the leaves that were not present without the clay.
These and other examples are beginning to alter scientists understanding, not only of clay eating, but of the roots of medicine itself.
“Geophagy, the ingestion of nonfood, falls into the realm of medicine,” says Johns. “As a medicine to alleviate discomfort, clay is not different from any drug that humans in industrial and preindustrial societies take in attempting to modify their physiological state.”
Eating clay, far from an eating disorder, may instead be history's earliest example of using the earth's resources to solve medical problems. With recent evidence revealing clay's common use in lowering food toxicity and promoting digestive health, this ancient practice may continue to have much to teach us about medicine and healing.
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