I. OverviewAseating disorders have begun to become more widely recognized by the public and medicalfield, there are still several eating disorders that have yet to be aspublicized—Pica. Pica is defined as an eating disorder characterized by acraving for the ingestion of unusual and non-nutritious substances (Lacey,1990). The DSM-5 outlines the criteria in diagnosing an individual with Pica.The criterion includes the ingestion of nonfood substances for at least 1month, ingested substances are “inappropriate to the developmental level of theindividual,” and eating behavior is not due to the cultural norms (“Pica”,2017). It is also suggested that the individual is at least 2 years of agebefore being diagnosed (“Pica”, 2017).
Theprevalence of Pica is difficult to assess because of its underreporting and itsstigma (“Pica”, 2017). There are many forms that exist—pagophagia (ice eating),stachtophagia (cigarette ash eating), etc. (Moore & Sears, 1994).
For thepurpose of exploring the adaptive value of Pica through a Tinbergen lens, thisessay will focus on one subset, geophagia: the consumption of the earth, soil,and/or clay (Moore & Sears, 1994). II. Development andMechanismStudiesinto the mechanism underlying geophagia and its incidence through developmentsuggest that there may be a connection between mechanism and development. Althoughthe underlying mechanism of this eating disorder is not fully understood, onehypothesis is mineral deficiencies cause an individual to develop geophagia(Rose et al., 2000). This idea stems from observations where geophagic patientsare frequently iron deficient, and when this iron deficiency is treated, theeating disorder subsides (Rose et al., 2000).
Iron is crucial in hemoglobin synthesis,and its deficiency is dangerous because it may lead to anemia, a severe stageof iron deficiency (Yadav & Chandra, 2011). Low iron levels result in an insufficientamount of oxygen in tissues and negative effects upon cellular and bodilyfunctions (Yadav & Chandra, 2011). These negative consequences result indownstream effects of “abnormal growth and behavior” (Yadav & Chandra,2011). Precisely, iron deficiency may have adverse effects on cognitivefunction and brain development (Yadav & Chandra, 2011). AlthoughPica may occur at any age, statistics indicate that infants, children, andpregnant women commonly fall victims (“Pica,” 2017; Woywodt & Kiss, 2002). Infantsare at a greater risk of iron deficiency compared to other developmental stages(Moy & Early, 1999). This increased risk may be due to an earlyintroduction of cow’s milk, a poor iron source (Moy & Early, 1999).
It isimportant that infants after the age of 4 months obtain iron throughsupplements or diet (Moy & Early, 1999). Unfortunately, parents often failto do so (Moy & Early, 1999). It has been distinguished that infant irondeficiency tends to coincide with when the brain undergoes a growth spurt(Yadav & Chandra, 2011). These iron deficient children are later seen to”have lower IQ scores, decreased attentiveness,” and decreased academicexcellence compared to non-iron deficient children (Yadav & Chandra, 2011).Furthermore, Pica is found to be quite prevalent within children withintellectual disabilities and autism (“Pica,” 2017). This suggests that theremay be some mechanistic link where iron deficiency causing alterations in thebrain lead to the development of Pica. III. MechanismDuringthe late fetal and early neonatal period, the hippocampus, a region of thebrain that is crucial in “learning, memory, and cognition,” is sensitive to lowiron levels (Radlowski & Rodney, 2013).
Low iron levels change the gene expressionthat is vital in the proper development and function of the hippocampus(Radlowski & Rodney, 2013). It may potentially be that the decreased ironlevels causing abnormal cognitive development of the brain also alter the same brainregion controlling for normal eating behaviors. An iron deficientdiet may result in unusual brain development that also results in geophagyonset. IV. PhylogenyGeophagic-eatingpatterns are prominent across the animal kingdom.
Geophagia is most commonlyreported in the bighorn sheep and other ungulates (Mincher et al., 2008). Theseungulates participate in “salt licking” to fulfill a sodium deficit (Mincher etal., 2008).
There is a case of Snowshoe Hares licking soils in iron rich areas(Roy et al., 2013). The hares participate in geophagy mostly during the winterand spring but hardly in the summer and autumn (Roy et al., 2013). Knowing thatnutritional stress is common in the winter and spring, it can be hypothesizedthat these hares display geophagy when there is a nutrient deficiency; thissupports an adaptive value behind geophagy (Roy et al., 2013). Furthermore, conservationof geophagy throughout the animal kingdom is indicative that there must be anadaptive value behind it or evolution would not have evolved this trait. V.
Adaptive ValueGeophagiais maladaptive because consistent ingestion of foreign substances may be toxicto the body, and there has been speculation that continual ingestion may leadto even lower iron levels since clay and soil inhibit iron absorption (Lacey,1990). However, embedded in the vulnerability to geophagia is the adaptivevalue to fulfill nutritional deficiencies in the short term and decrease thechances of anemia. Studies upon iron and calcium levels of geophagic materials proposea nutritional value behind them (Engberg, 1995).
Analysis of the ingested itemshas shown to provide 15% of the recommended iron and calcium daily allowancesto pregnant women (Engberg, 1995). Furthermore, a similar study upon locallyproduced clay in Latin America indicates that the clay delivers 9% of therecommended daily allowance for iron and other minerals (Engberg, 1995). Knowingthat anemia can lead to health complications such as fatigue, enlarged heart orheart failure, and potentially death, it would be adaptive to consume itemsthat would offset a potential anemia onset (“Anemia,” 2017). Ingesting earthmaterials continuously is maladaptive; when an individual notices theseabnormal eating behaviors, he/she must respond by fulfilling those nutritionalneeds through other options. In the short term, geophagy would serve to temporarilyfulfill nutritional deficits while also signaling these deficits to thepatient. Geophagy would be especially adaptive in a changing environment wherenutritional foods are not seasonally abundant.
VI. ExperimentOnemay test this adaptive hypothesis by utilizing rats and splitting them into twogroups. Both groups would be induced to be iron deficient, and the experimentalgroup would be fed geophagic substances. By evaluating the iron levels aftertwo weeks, if the hypothesis were to be true, the geophagic rats would haveimproved iron levels compared to the control. VII. SummaryBeinginformed of the geophagy’s adaptive value and looking at it comparatively helpsto destigmatize this disorder.
Geophagy may be maladaptive, but to a limitedextent, it can be adaptive in preventing the anemia onset especially withinchanging environments where nutritious foods vary.