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geophagy

 
Dictionary: ge·oph·a·gy   (jē-ŏf'ə-jē) pronunciation
n.
The eating of earthy substances, such as clay or chalk, practiced among various peoples as a custom or for dietary or subsistence reasons.

geophagism ge·oph'a·gism n.
geophagist ge·oph'a·gist n.

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Sci-Tech Encyclopedia: Geophagia
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Soil ingestion by animals. Grazing animals such as sheep and cattle ingest varying amounts of soil when they graze herbage contaminated with it. Pastures become contaminated with soil when livestock walk across the herbage, particularly in wet conditions.

The amount of soil ingested by sheep and cattle is influenced by soil type, stock density, earthworm activity, management practices, and various seasonal factors. Soils that are well drained and have a strong structure do not break up so readily and contaminate the herbage as is the case for poorly drained, weak-structured soils. When the density of stock grazing in a given area of herbage is increased, the amount of treading is increased, while the herbage is grazed more closely. The overall effect is that more soil is transferred to the herbage and ingested.

Geophagia is subject to seasonal variations. The wetter and cooler conditions of autumn and winter result in muddier herbage and an increase in soil ingestion by grazing animals. During the spring and summer, the greater growth of the herbage and drier conditions result in cleaner herbage, and there is a marked decrease in intake of soil.

Soil can be a source of mineral nutrients. Since soils are higher than herbage in iron, manganese, zinc, copper, cobalt, selenium, and iodine, they may contribute to the mineral nutrition of the grazing animals. See also Agriculture; Soil chemistry.


Geophagy, the consumption of earth, is widespread in various animal taxa, including birds, reptiles, and mammals. Among the latter it is reported in rats, ungulates, and primates, and in many human populations. The most frequently consumed soils are generally rich in clay, and the qualities of clay appear to be the stimulus for geophagy. The prevalence of this practice suggests that it is not aberrant behavior, but rather that it may have some functional significance related to diet and ecology. Several overlapping hypotheses have been proposed to explain the existence of geophagy, and clay consumption in particular: (1) clay provides supplemental minerals that may be lacking in the routine diet; (2) clay has the capacity to adsorb toxic secondary compounds widely distributed in plant foods; (3) clay protects the gastrointestinal tract from chemical and biological insult, and thus counters gastrointestinal disease. Support exists for all of these hypotheses depending on ecological context and taxon and indicates that geophagy is likely to be associated with positive biological effects.

The unique chemical structure of clays allows them to have these biological functions. Clays are associated with a variety of soil types, and are formed by routine weathering forces. All clays have similar properties: a large surface area, which derives from the organization of silicon-oxygen tetrahedrons in hexagonal networks, and an ability to bind and exchange minerals because of the dense localization of hydroxyl ions and oxygen in the tetrahedron structures. Clays are commonly composed of aluminum, magnesium, iron, and calcium, which can engage in mineral exchanges. Clays also have colloidal properties that make them adsorbent of water and other organic compounds. Commonly consumed clay types include: kaolin, smectite, montmorillonite, halloysite, and allophane.

Geophagy is well-described among ungulates, which seem to derive significant mineral nutrition (especially sodium, calcium, and magnesium) from eating earth, and among rats, who appear to use clay to detoxify a highly omnivorous and opportunistic diet. Gilardi and others found that parrots in Peru consumed large amounts of clay-rich soils, which served to detoxify a seed-based diet that was high in secondary compounds and to protect the cells that line the gastrointestinal tract from these toxic chemicals. Within the primate order, apes and monkeys consume soils that contain valuable minerals along with the clay metahalloysite, which counteracts diarrhea.

Among humans, the consumption of clay takes a variety of forms. In some cultural contexts, clay is an integral part of cuisine. Timothy Johns has documented the use of clay sauces with potatoes among highland Andean populations. Consumed in this way, clay adsorbs the toxic glycoalkaloid (solanine) in the potato cultigens that are the staple foods of this region. Clay is also used in the production of acorn bread by both Native Americans and Sicilians (Johns and Duquette, 1991). In this example, baking with clay reduces the toxicity of tannins in acorns, and improves the overall nutrient composition of this food. Clay is also used for specific medicinal purposes, most often to counteract gastrointestinal illness such as nausea, heart-burn, or diarrhea (Vermeer and Ferrell Jr., 1985). Consumed in tablet or liquid suspension (as in Kaopectate®), clay has these effects by slowing gastrointestinal motility, binding toxins or pathogenic microorganisms, and buffering acids of the upper gastrointestinal tract. It is important to note that since clay can adsorb a variety of chemical compounds, it can also interfere with the absorption of pharmaceuticals such as antimalarial drugs (chloroquine).

Beyond the routine use of clay in cuisine, clay consumption is often correlated with pregnancy in humans (Lagercrantz, 1958). The practice is reported most frequently among Africans and African Americans, although it is found in many other populations. Women report that clay eases the nausea and vomiting that often occur during the first trimester. This is likely due to the ability of clay to buffer the gastrointestinal tract and adsorb toxins, to which the embryo is especially vulnerable during early development. Clay consumption often continues throughout pregnancy, and clay may provide supplemental calcium, the demand for which increases during pregnancy to form the fetal skeleton. Support for this analysis comes from Andrea S. Wiley and Solomon H. Katz's study (1998) of geophagy in African populations, which demonstrated that clay consumption was significantly more common in populations that did not consume milk and that relied heavily on toxin-rich plant foods. Hence clay may serve as a detoxicant as well as a source of calcium; both are particularly important for nondairying, agricultural populations. Many sub-Saharan African clays (especially those derived from termite mounds) have been found to be rich in calcium (Hunter, 1993). Importantly, clays are frequently baked before consumption, thus reducing the potential for microbial contamination. When clay is not readily available, laundry starch is sometimes consumed by pregnant women, although this is not likely to be associated with the same health benefits as clay.

Acorn Bread

Processing of acorns for consumption is laborious and time-consuming, but the large quantity of tannins in acorns makes them inedible unless some mechanism for their removal is employed. In traditional Native American cuisine, acorns were first hulled (sometimes after boiling, to make it easier to extract the nutmeats) and pounded into a coarse flour with a stone mortar and pestle. Then, a variety of leaching techniques could be employed, including putting the flour in a basket or woven bag or digging a hole in a sandy bank along a river and allowing water to flow through the flour for up to several days. Or the flour could be put in a hole in the ground that was lined with leaves or pine boughs; water was then poured over it numerous times. The leaching removed the bitter tannins, thereby making the acorn flour both more palatable and more digestible. The flour was then placed into a tightly woven basket with water and very hot rocks to make a boiled acorn mush. It could also be molded into patties and fried, or the flour could be dried and then made into a stiff dough and slowly baked in a smoldering fire to produce bread. In contexts where leaching was not practiced or was insufficient to reduce the bitterness of acorns, acorn meal was mixed with clay and water and baked in an earth oven for several hours to produce acorn bread.

Bibliography

Hunter, John M. "Macroterme Geophagy and Pregnancy Clays in Southern Africa." Journal of Cultural Geography 14, no. 1 (1993): 69–92.

Johns, Timothy, and Martin Duquette. "Detoxification and Mineral Supplementation as Functions of Geophagy." American Journal of Clinical Nutrition 53 (1991): 448–456.

Lagercrantz, Sture. "Geophagical Customs in Africa and among the Negroes in America." Studia Ethnographica Upsaliensia 17 (1958): 24–81.

Vermeer, Donald E., and Ray E. Ferrell Jr. "Nigerian Geophagical Clay: A Traditional Antidiarrheal Pharmaceutical." Science 227 (1985): 634–636.

Wiley, Andrea S., and Solomon H. Katz. "Geophagy in Pregnancy: A Test of a Hypothesis." Current Anthropology 39, no. 4 (1998): 532–545.

—Andrea S. Wiley

Wikipedia: Geophagy
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The red-and-green macaw eats clay from exposed riverbanks, allowing it to utilize nutrients in harmful foods.

Geophagy is the practice of eating earthy or soil-like substances such as clay, and chalk, in order to obtain essential nutrients such as sulfur and phosphorus from the soil. This practice is widespread among animals in the wild, as well as in human societies. Human geophagy is closely related to pica, a classified eating disorder in the DSM-IV characterized by abnormal cravings for nonfood items[1].

The many possible health benefits of geophagy remain under study and are much debated. Since it is very common among animals, there is clearly some evolutionary advantage in this behaviour.

Geophagy is most often seen in rural or preindustrial societies among children and pregnant women.[2]

Contents

Animal geophagy

Geophagy is extremely widespread in the animal kingdom. Galen, the famous Greek philosopher and physician, was the first to record the use of clay by sick or injured animals back in the second century AD. This type of geophagy has been documented in "many species of mammals, birds, reptiles, butterflies and isopods, especially among herbivores."[3]

Geophagy is well documented in birds. Notably, many species of South American parrots have been observed at clay licks, whilst Sulphur-crested Cockatoos have been observed ingesting clays in Papua New Guinea (Discover, 1998) as well as in Glenbrook in Blue Mountains of Australia (Parrots Magazine, 2000). Analysis of most soils consumed by wild birds show that they prefer soils with high clay content, often with the smectite and bentonite clay families being well represented. In vitro and in vivo tests of these soils indicate that they release biologically important quantities of minerals like calcium and sodium, as well as adsorbing substantial quantities of small charged compounds such as alkaloids. Because the clays release minerals and adsorb other cations as part of the same process of cation exchange, it remains challenging to determine which function is the more important motivator in any given instance of avian geophagy. Separate from soil ingestion, pet birds are often provided with grit which is retained in their gizzards to aid in grinding the food they eat.

Human geophagy

There's considerable evidence to indicate that humans practised geophagy from the earliest times.

In human prehistory

Some scholars believe that prehistoric ancestors such as Homo erectus and Homo neanderthalensis used ochres to cure wounds as well as paint caves. Ochres are a mixture of clay and iron hydroxides.

"The oldest evidence of geophagy practiced by humans comes from the prehistoric site at Kalambo Falls on the border between Zambia and Tanzania (Root-Bernstein & Root-Bernstein, 2000)." Here, a calcium-rich white clay was found alongside the bones of Homo habilis (the immediate predecessor of Homo sapiens).[4]

Anthropological and historical evidence

Geophagy is nearly universal around the world in the tribal and traditional rural societies (although apparently it has not been documented in Japan and Korea). Also, the eating of clay (a form of geophagy) has been documented in historical sources beginning with Ancient Mesopotamia and Egypt. (Also see under medicinal clay.)

Geophagy was practiced by Native Americans in California and Peru who would eat earth with acorns and potatoes to neutralize potentially harmful alkaloids. Clay was used in the production of acorn bread in California and Sardinia, Italy.

Current practice

While Geophagy is most often seen in tribal and rural societies among children and pregnant women, it is practiced by members of all races, social classes, ages, and sexes. In some parts of the world, geophagia is a culturally sanctioned practice. In many parts of the developing world, earth intended for consumption is available for purchase.

In parts of Africa, rural areas of the United States, and villages in India, clay consumption is correlated with pregnancy and some women eat clay to eliminate nausea, possibly because the clay coats the gastrointestinal tract and may absorb dangerous toxins. The clay may also provide critical calcium for fetal development (Vermeer).

In Haiti, the poorest economy in the Western Hemisphere, geophagy is widespread. The clay mud is worked into what looks like pancakes or cookies, called "bon bon de terres" (bon bons of the earth), that are dried in the sun and sold throughout the poorer areas. Small amounts of other ingredients, vegetable shortening, salt and sometimes sugar, are also added to the mix. The cookies have little or no nutritional value and are associated with various health problems.[5][6]

While in the US and Europe the practice has often been stigmatized, this is not necessarily so in other parts of the world. Most non-western societies consider geophagy to be an adaptive, beneficial, and nutritional approach to promote health. There's a trend in recent scientific research to study geophagy not as a pathology, but rather as an "adaptive behavior" that supplements the diet with essential nutrients or treats a disorder such as diarrhea.[7]

Bentonite clay is available worldwide as a digestive aid; kaolin is also widely used as a digestive aid and as the base for some medicines. Attapulgite, another type of a clay, is an active ingredient in many anti-diarrheal medicines.[8]

Geophagy in the United States

Geophagy represents the fusion of societal nature and beliefs outside of the western world. Non westerners see dirt and clay as natural crucial elements of the world with symbolic features. This sharply contrasts the western view of dirt as impure and contaminated.[9] This given perception explains the western world's negative connotation and repulsion with geophagy. There are also several other reasons why geophagy is considered in America to be a pathology or an eating disorder. One such reason is that geophagy is strongly associated with a minority practice. It has a stigma of being an eating habit of African slaves and poor African-Americans. Geophagy was common among slaves who were nick-named "clay-eaters" because they had been known to consume clay, as well as spices, ash, chalk, grass, plaster, paint, and starch.[10] This stigma presents a road-block to the spreading of the practice of geophagy to the suburban white upper-middle class.[11] Geophagy has been declining because it is deemed socially unacceptable to make dirt part of the diet.[12]

Another factor keeping geophagy out of common practice for Americans is likely its association with a female practice. Geophagy is often associated with women, and most commonly, pregnant women. This presents an issue as American culture does not regularly distinguish between male and female foods.[13] The dominant Victorian ethic in American ideology is amongst the multiple reasons that "Geophagy" became stigmatized in American culture. An ability to control appetite coupled with eating seldomly was the appropriate measure of behavior in a "civilized' American culture. Engaging in and acting upon a craving for dirt was considered uncivilized because it was seen as having a lack of self-control. A person embodying the Victorian ethic would maintain a thin figure as well as refraining from alcohol and sex. Therefore, invoking the act of "geophagy", where craving and consumption of dirt was immense, was seen as a violation to the civilized American.[14]

Nevertheless, until recently clays like activated attapulgite and diosmectite were the active ingredient in over the counter antidiarrheal medications as they were and are among the most effective available treatment.

Future

In the past, women who wanted to become pregnant followed the eating patterns of successful mothers instead of changing their diet according to medical studies and recommendations. As a result, geophagy has continued to pass from generation to generation. Cooked, baked, and processed dirt and clay are sold in health food stores and rural flea markets in the South. Researchers have noticed that geophagy is not as prevalent as it once was as rural Americans assimilate into urban culture. In order for geophagy to remain a part of American culture, more effective marketing strategies need to be implemented that fit into modern American culture.[15]

While the marketing of dirt in its original form would most likely not sell in the American market, geophagy may have a possible future if companies break up the dirt into its components. Several minerals or consitutents of dirt have varying therapeutic purposes. For instance, antacids or anti-diarrhea medications contain several consitutents of dirt. Although the chalky pink liquid gives a very different impression to buyers than raw earth, Americans still practice geophagy in a certain sense. Also, as described before, Americans regard the practice of digging raw dirt for consumption as a wholly uncivilized act. Yet, the American culture could potentially continue to practice geophagy if a company marketed the dirt. The future of geophagy in the United States seemingly depends upon scientific backing, and the creation of a market or company to provide the dirt to consumers.[16]

Classification and diagnosis

The International Classification of Diseases includes geophagia among eating disorders (F50) as a variety of pica, the ingestion of non-foods. However, dirt can constitute a source of iron, although the bioavailability of such mineral has not been ascertained. For example, red clays often have iron in ferrous form, poorly absorbed by humans.

It is also associated with iron deficiency (see Health A to Z, below)

Geophagia can be diagnosed, in absence of other evidence, by measuring the concentration of silica in feces.

Cultural explanations

The cultural meaning of dirt may be another factor that contribute to making geophagy an unacceptable practice in some cultures. Western cultures view dirt as being filthy, especially after the rise of germ theory. Dirt is similar to miasma, in that theory, which is a place where diseases are made and spread. Eating the miasma would be heretical, if not suicidal.

Furthermore, one overarching theme of Western culture is a distancing from the natural world and progress toward technology and efficiency. This movement would render geophagy unacceptable to Westerners. Evidence for this comes from the English language, with phrases like "dirt cheap" and "dirty dog." In non-western cultures, soil is thought of as being a provider for the Earth to grow, and therefore it has nutrients which can be absorbed. It came from a/the god(s) and nourishes the crops which feed the culture. In these cultures, the acceptance is not only seen by secluded tribes, but it is also accepted into the market and into families.

The persistence of geophagy within a family or community can also partially be explained by a simple mother/daughter sharing mechanism. A crucial and sometimes hazardous part of rural communities is the act of giving birth. Without advanced medical knowledge, local customs become key to a healthy outcome. Geophagy enters the picture when daughters would "follow the diet of a woman that they knew had been successful at giving birth".[17] The maternal chain can therefore act as an important vector in the continuance of this act. The practice, in truth, is important because it does provide much needed minerals to the human body. Indeed, Western cultures have continued the practice of geophagy, but only under the guise of vitamins and minerals.

Impact on health

Health benefits

In a Science Digest article (Paraquat: a Potent Weed Killer is Killing People[18]), it is recommended that a paraquat poisoning victim promptly swallow dirt, even at the risk of salmonella, because paraquat is deactivated upon contact with soil. Otherwise, a sufficiently lethal dose would cause damage to the liver, kidneys, and especially the lungs, usually causing death by asphyxiation by causing severe fibrosis. Lung transplants in two victims merely delayed their deaths because chemical levels still in their bodies subsequently damaged the transplanted lungs, too.

There is also evidence that supports the usefulness of the flora found in soil. Some have even suggested that it is useful, if not vital, in the establishment of healthy bacteria within the digestive tract, addressing the problems presented by Crohn's Disease and Leaky Gut Syndrome. Highly adsorbent families of clays have been demonstrated to cause the lining of the vertebrate gut to change both on a cellular and acellular level, potentially protecting the gut from chemical insults as well as alleviating ailments such as esophagitis, gastritis, and colitis.

Chimpanzees in Kibale National Park, Uganda have been observed to consume soil rich in kaolinite clay shortly before or after consuming plants including Trichilia rubescens, which possesses antimalarial properties in the laboratory. Simulated mastication and digestion reveals that the clay helps to release active antimalarial components from the leaves. The same type of soil is used by local healers to treat diarrhea,[19] presumably by the same mechanism as over-the-counter antidiarrheal preparations.

Health risks

Like coprophagia, it may be dangerous because parasite eggs can be passed in animal feces. Baylisascaris eggs, for instance, are dropped millions at a time by raccoons and other wildlife. They can stay dormant for years, remaining viable even in extreme temperatures and drought. Some of these roundworm eggs may remain in the soil long after the feces have decomposed, and become active in the digestive tract upon being consumed. Children's predilection to engage in geophagia makes them more susceptible to worm infestations.

Other dangers associated with geophagia include damage to tooth enamel, the ingestion of a variety of bacteria, lead poisoning and intestinal obstruction.

There is a psychological hypothesis, which is centered around the craving ideas, reported by clay eaters. The researchers attention was directed mainly towards the pregnant and postpartum women and their emotional state. Geophagy was attributed to feelings of misery, homesickness, depression, and alienation.[20]

In popular culture

  • In One Hundred Years of Solitude, by Gabriel García Márquez, Rebeca exhibits symptoms of geophagy by secretly and compulsively eating the soil in the yard.
  • In the 1937 film adaptation of Pearl S. Buck's The Good Earth, during a prolonged drought, O-Lan (Luise Rainer) serves the children something to eat. Neighbors desperate for food discover that she had fed them the good earth itself, because, as she says, it is warm and gives life.
  • In the novel Survivor by author Chuck Palahniuk, (Page 172), one female Creedish cult survivor is said to have killed herself after eating dirt, or committing "Geophagy", until she experienced an esophageal rupture.
  • salad fingers, from the cartoon of the same name suffers from geophagy as well as other forms of pica
  • The idiom "to eat dirt" means to humble or humiliate oneself.

Notes

  1. ^ http://www.enotes.com/mental-disorders-encyclopedia/pica
  2. ^ Peter Abrahams, Human Geophagy: A Review of Its Distribution, Causes, and Implications. in H. Catherine W. Skinner, Antony R. Berger, Geology and health: closing the gap. Oxford University Press US, 2003, p. 33. ISBN 0195162048
  3. ^ Jared M. Diamond, "Evolutionary biology: Dirty eating for healthy living". Nature 400, 120-121 (1999)
  4. ^ Olle Selinus, B. J. Alloway, Essentials of medical geology: impacts of the natural environment on public health. Academic Press, 2005 ISBN 0126363412, p. 446
  5. ^ [1] May 27, 2009 Worldfocus
  6. ^ Dirt poor Haitians eat cookies made of mud February 19, 2009 Worldfocus
  7. ^ Henry and Kwong, "Why is geophagy treated like dirt?"
  8. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 366
  9. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 354
  10. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 355
  11. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 357
  12. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 368
  13. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 360
  14. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 358-59
  15. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 366-368
  16. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 366-368
  17. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 365
  18. ^ Revkin, A. C. 1983. Paraquat: A potent weed killer is killing people. Science Digest 91(6):36-38, 42, 100-104.
  19. ^ "Down to earth remedies for chimps:Study suggests chimpanzees ingest soil to enhance anti-malarial properties of plants". http://www.springer-sbm.com/index.php?id=291&backPID=132&L=0&tx_tnc_news=3965&cHash=cd0b6a81b0.  - press release about study to be published soon: Krief S, Klein N & Fröhlich F (2008). Geophagy: soil consumption enhances the bioactivities of plants eaten by chimpanzees. Naturwissenschaften (DOI 10.1007/s00114-007-0333-0)
  20. ^ Henry and Kwong, "Why is geophagy treated like dirt?", p. 355

References

  • Peter Abrahams, Human Geophagy: A Review of Its Distribution, Causes, and Implications. in H. Catherine W. Skinner, Antony R. Berger, Geology and health: closing the gap. Oxford University Press US, 2003. ISBN 0195162048
  • Callahan, G.N. (2003). "Eating dirt". Emerging Infectious Diseases 9 (8): 1016–1021. http://www.cdc.gov/ncidod/EID/vol9no8/03-0033.htm. 
  • Cooper, D.W. (2000). "Clay Eating Parrots". Parrots Magazine 36. 
  • Dominy, N; Davoust, E; Minekus M (2004). "Adaptive function of soil consumption: an in vitro study modeling the human stomach and small intestine". Journal of Experimental Biology 207: 319–324. doi:10.1242/jeb.00758. PMID 14668315. 
  • Vermeer, D.E; Frate, D.A. (1975). "GEOPHAGY IN A MISSISSIPPI COUNTY". Annals of the Association of American Geographers 65 (3): 414–416. doi:10.1111/j.1467-8306.1975.tb01049.x. 
  • Hamilton, G. (1998). "Let them eat dirt". New Scientist 159 (2143): 26–31. 
  • Harvey, P; Dexter, P; Darnton-Hill, I (2000). "The impact of consuming iron from non-food sources on iron status in developing countries". Public Health Nutrition 3 (4): 375–383. doi:10.1017/S1368980000000434. 
  • Kwong, A.M.; Henry, J. (2003). "Why is geophagy treated like dirt?". Deviant Behavior 24: 353–371. doi:10.1080/713840222. 
  • Lagercrantz, S. (1958). "Geophagical Customs in Africa and among the Negroes in America". Studia Ethnographica Upsaliensia 17: 24–81. 
  • Laufer, Berthold (1930). Geophagy (available online). Chicago: Field Museum Press. http://www.archive.org/stream/geophagy182lauf/geophagy182lauf_djvu.txt. 
  • Reid R (1992). "Cultural and medical perspectives on geophagia". Medical Anthropology 13 (4): 337–351. 
  • Vermeer, D. (1971). "Geophagy Among the Ewe of Ghana". Ethnology 10: 56–72. doi:10.2307/3772799. 
  • Vermeer D (1966). "Geophagy among the Tiv of Nigeria". Annals of the Association of American Geographers 56 (2): 197. doi:10.1111/j.1467-8306.1966.tb00553.x. 
  • Walker, A; Walker, B (1997). "Pica". Journal of Social Health 117 (5): 280–284. doi:10.1177/146642409711700503. 
  • Wiley, Andrea S. (2003), "Geophagy", in Katz, Solomon H., Encyclopedia of Food and Culture, 2, New York: Charles Scribner's Sons, pp. 120–121 
  • Wiley, A.S.; Solomon, H.K. (1998). "Geophagy in Pregnancy: A Test of a Hypothesis". Current Anthropology 39 (4): 532–545. doi:10.1086/204769. 
  • Wong, M.; Simeon, D. (1993). "The silica content of faeces as an index of geophagia: its association with age in two Jamaican children's homes.". Journal of Tropical Pediatrics 39 (5): 318–319. 
  • Ziegler, J. (1997). "Geophagia: a vestige of paleonutrition". Tropical Medicine and International Health 2 (7): 609–611. doi:10.1046/j.1365-3156.1997.d01-359.x. 

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