PICA is an eating disorder characterized by the consumption of nonnutritive substances. One category of PICA is geophagia (or geophagy), the consumption of dirt, soil, or clay. Geopaghy has been recorded in 1000 AD and most countries have populations (in both animals and humans) have been found to consume it.1 Currently, geophagy is found most prominently in pregnant women and children as well as those in developing countries. Currently geophagy is has been found to be practiced largely in African and Hispanic communities worldwide. In America, it is predominant in Southern Blacks and Hispanics. There are many theories as to why geophagy is predominant in pregnant women: the hunger, nutrition, and protection hypotheses.
The first hypothesis is the hunger hypothesis. It states that geophagy occurs to ease hunger pains and feel full.1,4,5 According to this theory, there are no nutritional benefits. It also explains that consuming dirt is palatable due to nutrient deficiencies causing epiphenomena1 and hypogeusia1,2. Hypogeusia is a zinc deficiency, which diminishes taste. Geophagic earth leaches more zinc in the GI tract, repeating the cycle upon consumption.2 Epiphenomena is a secondary phenomenon occurring alongside the primary. In this case, it is a neurological and sensory issue, which affect appetite-regulating brain enzymes.1 There are four main implications of the hunger hypothesis: (1) Geophagists don’t consume enough to be full. The amounts consumed are small, like medicine, rather than a meal.1, 5 (2) Geophagy doesn’t occur most often in times of famine or food shortages.1 In addition, only 22% of geophagists claim to consume earth due to hunger and another 50% reports hunger was not associated with geophagic behavior.1 (3) If geophagy occurred only to feel full, any soil would be sufficient. However, 93% of reported geophagists wanted a specific soil type, usually clay-rich.1 (4) Geophagic behavior doesn’t occur in relation to caloric requirements.1 Women require fewer calories than men. However, women are practice geophagy more.1 In terms of pregnant women, they require more calories in late gestation when the fetus is large and growing faster. However, geophagy is found practiced most during early gestation.1 Lactating women also have the greatest caloric requirements of all age groups but are not the most frequent geophagists.1 In summary, the hunger hypothesis implies that geophagy occurs to feel full. However, the quantity and quality of soil and timing of geophagy in the environment are inconsistent with the hypothesis. The second and most discussed hypothesis is the nutrient deficient hypothesis.
The nutrient deficient hypothesis states geophagy occurs due to a lack of iron, zinc, or calcium.1,4,5 There are four main counterarguments to the nutrient hypothesis: (1) Geophagy doesn’t occur in conjunction with a deficiency. It is associated with anemia1,2,3, hypokalacmia1,2, 3, and hypogeusia2. Studies have also shown that women who ate geophagic material tended to have lower iron and zinc levels. However, there is insufficient evidence of a casual relationship.1 (2) When associated nutrient deficiencies are resolved, geophagy doesn’t stop. Studies have found that neither iron, calcium, or multivitamins changed geophagic behaviors.1 There is limited data to make a conclusion about zinc supplementation.1 (3) The highest population of geophagy do not have the highest needs of iron, zinc, and calcium, especially regarding pregnant women.1 Iron is needed less in early pregnancy due to loss of menstruation, but more in late gestation for the developing fetus. Similar, calcium is needed in higher quantities at late gestation for fetal skeleton growth. Zinc recommendations do not change throughout pregnancy. Based on this, geophagy should be most prevalent during late pregnancy. However, it is not. Geophagy occurs twice as often in early gestation.1 (4) There is contradictory evidence to the bioavailability of soil nutrients.1,2,3 Studies state that geophagy decreases1,2,3 or has limited effect6 on micronutrient states (e.g.; iron and zinc). Other studies find that geophagy may increase or have no effect on macronutrient states (e.g., calcium).1,4 Nutrient supplementation is based on soil mineral solubility in the gastrointestinal tract and nutrient binding capacity of the soil.3 The soil analyses showed soil can remove from the GI tract, but that iron sorption can increase iron supplies. (5-9 ug can be obtained from a 1 gram sample of soil).3 Similar results were found for zinc. Calcareous soils were found to have varying degrees of desorption implying they may be a source for supplementation. In total, the analyses found that 28 grams of soil per day can remove 25-30% and 17-20% of RDA for iron and zinc.3 They also found that geophagists typically have diets high in phytate, which decreases the bioavailability of iron, zinc, and calcium.3 However the studies also found that soil may supplement the micro-and macronutrients when stores are depleted.3 In summary, the nutrient deficiency hypothesis proposes that geophagy occurs due to a lack of nutrients. However the non-correlation with a deficiency, no cease of behavior when supplementation is provided, the timing of geophagy in the life cycle, and ambiguous bioavailable of nutrients are inconsistent with the hypothesis. The third and most supported hypothesis is the protection hypothesis.
The protection hypothesis states that geophagy occurs as a medication to improve the secretory immune system.1,2,4,5 It proposes that the microorganisms in soil help reduce the short-term effects of malaise and long terms effects of toxins, parasites, and pathogens in plants and other bacteria.1 Common plant toxins consumed are tannins and glycoalkaloids.1
Common chemicals consumed by food- and waterborne bacteria are enterotoxins: Escherichia coli, Staphylococcus aureus, Salmonella enterica, and Listeria monocytogenes.1 Consuming toxins can cause gastrointestinal distress, dizziness, muscle pains, and cancer. There are two hypotheses to explain the mechanism behind geophagy amplifying the immune system: (1) The soil reduces the permeability fo the intestinal gut wall to toxins and pathogens.1 (2) The soil binds directly to toxins, pathogens, and other parasites.1 This makes them un-absorbable in the gut and inhibit their respiration. This mechanism is the most supported mechanism with findings showing that clay binds to multiple pathogens: viruses, bacteria, toxins (herbicides, pharmaceuticals, and secondary plant compounds).1 Through these mechanisms, it is suggested that clay acts as an adjuvant, like aluminum salts.4 The clays consumed by pregnant women are typically high in aluminum.4 This increases the immunoglobin antibodies (IgA) against the organic antigens found in the clay. These may appear in the breast milk and help newborns by IgA preventing the attachment of bacteria and viruses at the mucosal surface.4 The protection hypothesis is sorted by four main arguments: (1) Geophagic earth is not typically a vector for geohelminth transmission.1 This is because geophagists usually select subsoils that are 60 to 90 centimeters below the soil surface.4 These are less likely to contain eggs found closer to the surface. In addition, 98% are cooked before consumption.1 Also, there is very little evidence of transmission due to geophagy in adults. (2) Geophagy is associated with GI distress. Malaise is associated with geophagy in 98% of cases.1 Also, over-the-counter stomach remedies (e.g., Maalox and Kaopectate) also contain clay in its ingredients.2,4 In pregnant women, geophagy helps detox the body to cure morning sickness.2 Morning sickness occurs most often in the first trimester when geophagy is most prevalent.2 (3) Geophagy occurs more frequently in populations with higher exposure to toxins, parasites, and pathogens.1 Pregnant women are usually immunosuppressed to avoid rejecting their embryo. They also tend to consume more and are more susceptible to damage from teratogens in early gestation. This is supported cause the highest occurrence of geophagy is pregnant women within their first trimester.1 (4) Geophagy occurs more frequently in populations with higher exposure to food-borne illness.1 Food-borne pathogens tend to occur more in hot, humid, and tropic climates. Despite geophagy occurring worldwide, it appears most frequently found in warmer climates.1 In summary, the protection hypothesis states that geophagy occurs to improve the immune system. The correlation with GI distress, few occurrences of pathogen transmissions, high frequency in equatorial climates, and timing of geophagy in the lifecycle are consistent with the protection hypothesis. However, despite the positive impacts associated with the protection hypothesis, there are also many negative correlations.
The most studied association between geophagy and pregnant women is iron-deficiency anemia. Pregnant women require 300 mg of iron, but some studies state that geophagy may reduce it.1 Anemia in pregnant women can lead to high-risk pregnancies, premature delivery, and neonatal anemia in the fetus. This can not only be deadly for the mother and child but also cause irreversible mental and physical deformities due to neural tube defects. In turn, this could cause newborns to be even more susceptible to lead poisoning and infections even as children, who are another high population of geophagists. In total, despite the association between geophagy and anemia, but further evidence is needed to suggest a causal relationship. The relationship between anemia and geophagy demonstrate how geophagic tendencies can impact the entire lifecycle of not only the primary consumer pregnant women but also their fetus.
In conclusion, there are three hypotheses explaining the biological occurrence of geophagy: (1) hunger; (2) nutrient deficiency; and (3) protection. The protection hypothesis is the most widely supported hypothesis. Geophagy is most commonly reported in pregnant women. There are several health impacts associated with geophagy: iron deficiency anemia, hypokalemia, hypogeusia, parasitic and toxic infections, and mechanical bowel disorder. Iron-deficiency anemia is the most common. These impacts show how each stage of the lifecycle is connected to the previous stage; how negative impacts as a fetus can have long-term effects throughout one’s life.
Work Cited
1 Young, S., Sherman, P., Lucks, J., Pelto, G., & Rowe, L. (2011). Why On Earth?: Evaluating Hypotheses About The Physiological Functions Of Human Geophagy. The Quarterly Review of Biology, 86(2), 97-120.
2 Stokes, T. (2006). The earth-eaters. Nature, 444(7119), 543-4.
3 Hooda, P., Henry, C., Seyoum, T., Armstrong, L., & Fowler, M. (2002). The Potential Impact of Geophagia on the Bioavailability of Iron, Zinc and Calcium in Human Nutrition. Environmental Geochemistry and Health, 24(4), 305-319.
4 Callahan, Gerald N. (2003). Eating dirt. (Another Dimension).(Editorial). Emerging Infectious Diseases, 9(8), 1016-21.
5 Eating earth can be good for the belly, researcher finds. (2011, June 2). Retrieved May 06, 2018, from http://www.press.uchicago.edu/pressReleases/2011/June/QRB_1106_EatingDirt.html
6 Gretchen L. Seim, Elad Tako, Cedric Ahn, Raymond P. Glahn, & Sera L. Young. (2016). A Novel in Vivo Model for Assessing the Impact of Geophagic Earth on Iron Status. Nutr
ients, 8(6), 362.