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  • Dirt in diet. Benefit or hindrance? Modern societies, especially those in developed countries, have essentially stigmatized dirt eating over the past few centuries.
  • Yet careful scientific evaluation suggests that dirt eating arose holistically, most likely for health benefits.
  • Need is a strong word yet we are living through rather unprecedented times, coming  full circle in our understanding of the relevance of pica and in particular, geophagia, the practice of intentional and repeated ingestion of soil or other geological materials (1), especially chalk and clay. Pica is compulsive craving and eating of items culturally defined as ‘nonfood‘, while geophagia is derived from Greek, ge meaning earth and phag meaning eat.
  • Pica has remained more or less a mainstay in many traditional, poorer societies while the developed country mindset somewhat narrow-mindedly evolved to regard it as ‘uncivilized‘ and ‘unhygienic‘ to the extent of labeling it a psychopathology (2). Why narrow-minded? Because our definition of foodstuffs is after all inherently subjective, differing from culture to culture, and from one era to another. Lucretius understood this way back in the 1st century BC when he purportedly wrote, ‘quod ali cibus est aliis fuat acre venenum (what is food for one man may be bitter poison to others)’.
  • Many animals deliberately eat soil, often to detoxify food, obtain calcium or to self-medicate (3, 4).
  • For example, rats lack capacity to vomit. When exposed to poisons, they’re observed to eat kaolin clay, which reduces their poison-associated sickness and death (5, 6, 7, 8, 9).
  • Scientific observations are leading to a quite remarkable revision about utility of pica, especially geophagia among humans. See figure below from 10 for description of types of pica.


Eating dirt was considered important for health in antiquity (11).

  • In recorded western history, Hippocrates (ca. 460-377 BC) is first credited with noting geophagy, ‘ If a pregnant woman feels the desire to eat earth or charcoal and then eats them, the child will show signs of these things‘ (12).
  • Aristotle also observed soil ingestion for therapeutic and religious reasons.
  • Pedanius Dioscorides wrote De materia medica ca. 65 AD (13).
    • In it, he prescribes the red earth of Sinope for liver ailments. From Turkey near the Black Sea, it’s probably an iron oxide enriched clay.
    • And Samian earth (referred to as terra Samia from the Greek island of Samos) for detoxifying some poisons when swallowed with water.
  • Pliny the Elder‘s encyclopaedia (ca. 77 AD) (14) mentions
    • The stone of Samos was used for stomach and mind ailments, even giddiness.
    • Sinope clay for stopping menstruation.
    • Lemnian earth (terra Lemnia/terra Sigillata)
      • In vinegar for vomiting or spitting blood.
      • In water for spleen/kidney problems and for excessive menstruation.
      • For poisons and snake bites.
  • Galen recorded the process for making soil medicine from Lemnian earth (15).
  • Lemnian earth tablets were considered sacred, were trademarked using official seals and highly regarded for their medicinal (dysentry, plagues and poison antidote) and commercial value (11; see figure below).
  • Soranus of Ephesus was a 2nd century AD Ob-Gyn, pediatrician. He noted that pica in pregnant women usually started ~40days after conception, lasting about 4 months (16).
  • Aëtius of Amida (today called Diyarbakir in Turkey), wrote an obstetric textbook in the 6th century AD. In it, he writes,  ‘Approximately during the second month of pregnancy, a disorder appears that has been called pica, a name derived from a living bird, the magpie…Women then desire different objects… some prefer spicy things, others salty dishes and again others earth, egg shells or ashes‘ (12).
  • Álvar Núñez Cabeza de Vaca, traveling through modern-day southeastern US between 1528 and 1536, wrote of observing a tribe who ate soil to quench hunger during famine and mixed it with the fruit of the mesquite tree, Prosopis juliflora, to make it sweet and palatable (17).
  • Alexander von Humboldt observed geophagy by the Ottomac tribe in the Orinoco/Amazon basin in the 19th century. He wrote, ‘one of the most extraordinary physiological phenomena. They eat earth; that is they swallow every day, over several months, very considerable quantities, to appease hunger, and this practice does not appear to have any injurious effect on their health‘ (18), specifying they chose ‘the most unctuous earth, and the smoothest to the touch
  • Archeology now suggests that many major food plants we take for granted today, such as the potato, originally contained poisonous substances that required detoxificiation.
  • Potato is today the world’s most widely grown tuber and 4th largest fresh produce crop.
    • Before non-toxic mutants were isolated and propagated, its original domestication in South America required using ‘potato clays‘ to detoxify and render it edible.
    • For e.g., before eating, potatoes were dipped into aqueous kaolin clay suspension, locally called Chacco, to prevent ‘souring of the stomach‘ (19).
    • The clays used in this detoxification procedure effectively adsorb a glycoalkaloid called tomatine, a heat stable toxin not destroyed by cooking (20).


Is eating dirt considered important for health in modern times?

  • Research found Lemnian earth effective against metal poisoning. Presumed mechanism of action is through the ion exchange properties of this soil’s elements (21).
  • In Ghana (formerly the Gold Coast), black cotton soil (now called Vertisoils) was used to remove the toxin dioscorine to allow eating poisonous wild yam Dioscorea dumetorum during times of famine (11).
  • Activated charcoal treats many kinds of acute poisoning in humans and animals (22, 23).
  • Baked soil is widely used in Uganda for GI tract symptoms (24, see figure below).

 

 

  • An in vitro model to simulate digestion by the human stomach and small intestine confirmed that kaolin could effectively adsorb plant compounds such as tannins that deplete food quality (25).
  • Today, soil is even attractively packaged, advertised and sold as a panacea in reputed stores (26) and online (Page on whitedirt.com).
  • According to the detoxification and protection hypothesis (27, 28; see figure below), pica prevents harm by either
    • Binding with the GI (gastrointestinal) tract’s mucin layer. This improves gut wall impermeability.
    • Binding directly with pathogens or plant toxins. This detoxifies them by preventing their absorption by the gut.

 

Defects of previous research on pica

  • Examining pica through the lens of stigma necessarily precluded a holistic understanding.
  • This may be why pica remains mired in confusion and biased interpretation.
  • For example, even though there are hundreds of studies on pica, it wasn’t until 2011 that a meta-analysis of 278 studies uncovered that a major reason for eating dirt, specifically certain types of clay, was to relieve GI tract distress (29, see figure below).
  • Flawed methodologies of many studies also didn’t accurately assess potential bioavailability of various micronutrients from clay eating. Result? They either over- or under-estimated effects, both beneficial and harmful.

 

  • Studies also suggest that pica may provide essential micronutrients such as calcium, iron and zinc (11, see figure below).
  • Pica is typically seen during pregnancy and in young children, across geography, culture and time.
  • Compensatory mechanism for replenishing depleted micronutrient levels thus remains a compelling argument.
  • We need better designed studies to generate better supporting data.
  • We also need many more studies that explore links between pica and human microbiome in health and disease.

 

  • The full circle metaphor. Let’s complete it by taking a quick look at many of the active and inert ingredients in modern pharmaceuticals.
  • An abundance of clay minerals (30). Happenstance? Unlikely because of the preponderance of their beneficial properties
    • High specific area
    • High adsoprtive capacity
    • Helpful flow (Rheology) features
    • Chemically inert
    • Little/no toxicity
    • Cheap
  • Research on pica thus suggests that it is one of the antiquated practices that may well be based on cumulative wisdom, wisdom that we may have lost through time but could yet regain through rigorous and inclusive science.
  • Bottomline, a comprehensive analysis of eating dirt suggests many healthful benefits while carelessness in choice of material/soil has several harmful effects (see figure below using data from 31 and 11).
  • Since we liberally pockmarked and saturated post-Industrial Earth with an abundance of noxious detritus, much of the harm observed from pica may not be intrinsic so much as one of our making. After all, don’t we seem to have rather thoroughly defiled the earth?


Bibliography

  1. Chapter 7. Geophagia and Human Nutrition by Peter Hooda and Jeya Henry In Consuming the Inedible: Neglected Dimensions of Food Choice By Jeremy M. MacClancy, C. J. K. Henry, Helen Macbeth.
  2. American Psychological Association. 2011. Diagnostic and statistical manual of mental disorders, 5th ed. Washington, DC: American Psychological Association
  3. Limpitlaw, Ulli G. “Ingestion of Earth materials for health by humans and animals.” International Geology Review 52.7-8 (2010): 726-744.
  4. Abrahams, Peter W. “Geophagy and the involuntary ingestion of soil.” Essentials of medical geology. Springer Netherlands, 2013. 433-454.
  5. Mitchell, Denis, et al. “Poison induced pica in rats.” Physiology & behavior 17.4 (1976): 691-697.
  6. Burchfield, Susan R., Matthew S. Elich, and Stephen C. Woods. “Geophagia in response to stress and arthritis.” Physiology & behavior 19.2 (1977): 265-267.
  7. Watson, P. J., et al. “Inhibited drinking and pica in rats following 2-deoxy-D-glucose.” Physiology & behavior 39.6 (1987): 745-752.
  8. Takeda, Noriaki, et al. “Pica in rats is analogous to emesis: an animal model in emesis research.” Pharmacology Biochemistry and Behavior 45.4 (1993): 817-821.
  9. Madden, Lisa J., Randy J. Seeley, and Stephen C. Woods. “Intraventricular neuropeptide Y decreases need-induced sodium appetite and increases pica in rats.” Behavioral neuroscience 113.4 (1999): 826.
  10. Chapter 2. Consuming the Inedible: Pica behavior by Carmen Strungaru. In Consuming the Inedible: Neglected Dimensions of Food Choice By Jeremy M. MacClancy, C. J. K. Henry, Helen Macbeth.
  11. Abrahams, Peter W. ““Earth Eaters”: Ancient and Modern Perspectives on Human Geophagy.” Soil and Culture. Springer Netherlands, 2009. 369-398.
  12. Woywodt, Alexander, and Akos Kiss. “Geophagia: the history of earth-eating.” Journal of the Royal Society of Medicine 95.3 (2002): 143-146. Page on nih.gov
  13. Riddle, John M. Dioscorides on pharmacy and medicine. Vol. 3. Univ of Texas Pr, 1985.
  14. Rackham, H. “Pliny: natural history (volumes I–X).” (1938).
  15. Sweet, Jessie M. Sir Hans Sloane: life and mineral collection. Natural History Medicine, 5: 145-164. 1935.
  16. Temkin, Owsei. Soranus’ gynecology. Vol. 3. JHU Press, 1956.
  17. De Vaca, Alvar Nuñez Cabeza, Marco da Nizza, and Antonio de Mendoza. The Journey of Alvar Nuñez Cabeza de Vaca and His Companions from Florida to the Pacific, 1528-1536. AS Barnes, 1905.
  18. Keay, J. “Eating dirt in Venezuela.” The Robinson book of exploration. Robinson, London (1993): 344-350.
  19. Lawson, Alexander, and H. P. Moon. “A clay adjunct to potato dietary.” Nature 141.3557 (1938): 40.
  20. Johns, Timothy. “Detoxification function of geophagy and domestication of the potato.” Journal of Chemical Ecology 12.3 (1986): 635-646. Page on umich.edu
  21. Black, D. A. K. “A revaluation of terra sigillata.” The Lancet 268.6948 (1956): 883-884.
  22. Brown, Donald D., et al. “Decreased bioavailability of digoxin due to antacids and kaolin-pectin.” New England Journal of Medicine 295.19 (1976): 1034-1037.
  23. Cooney, David O. Activated charcoal in medical applications. CRC Press, 1995.
  24. Abrahams, Peter W. “Geophagy (soil consumption) and iron supplementation in Uganda.” Tropical Medicine & International Health 2.7 (1997): 617-623. Geophagy (soil consumption) and iron supplementation in Uganda
  25. Dominy, Nathaniel J., Estelle Davoust, and Mans Minekus. “Adaptive function of soil consumption: an in vitro study modeling the human stomach and small intestine.” Journal of Experimental Biology 207.2 (2004): 319-324. an in vitro study modeling the human stomach and small intestine
  26. Henry, Jacques, and Alicia Matthews Kwong. “Why is geophagy treated like dirt?.” Deviant Behavior 24.4 (2003): 353-371.
  27. Hui, Y. H., et al. “Foodborne Disease Handbook Volume 1: Diseases Caused by Bacteria.” (1994).
  28. Young, Sera L. “Pica in pregnancy: new ideas about an old condition.” Annual review of nutrition 30 (2010): 403-422.
  29. Starks, Philip TB, and Brittany L. Slabach. “The scoop on eating dirt.” Scientific American 306.6 (2012): 30-32. Page on omega3galil.com
  30. Carretero, M. I., C. S. F. Gomes, and F. Tateo. “.5 Clays and Human Health.” Developments in Clay Science 1 (2006): 717-741. Page on projects.itn.pt
  31. Chapter 5. A Vile Habit? The Potential Biological Consequences of Geophagia, with Special Attention to Iron by Sera L. Young. In Consuming the Inedible: Neglected Dimensions of Food Choice By Jeremy M. MacClancy, C. J. K. Henry, Helen Macbeth.

https://www.quora.com/Do-we-need-dirt-in-our-diets/answer/Tirumalai-Kamala

 

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