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Eating Earth: Exploring the Mysterious World of Geophagy

Posted By Mark Sisson On July 21, 2011 @ 9:50 am In Nutrition | 118 Comments

A few weeks ago I got into an unusual conversation with a guy in a coffee shop. We were both passing through town – he for personal travel and me for business. We struck up a conversation waiting in line and ended up chatting for the remainder of our respective stops there. We talked about what we did, where we were headed, etc. When I mentioned the blog and the PB philosophy behind it, his face lit up. He loved the idea and had embraced similar principles several years prior. His latest experiment, the health effects of which he raved about, was adding dirt to his diet. I listened with interest and asked questions.

You all know I’m big on dirt, and more specifically, on probiotic supplementation [7]. And while I’ve touched on the health benefits of dirt [8], the immune building properties of dirt consumption in children [9], and the connection between dirt and clinical depression in youngsters [10], I’ve never met anyone who made a personal habit of dirt ingestion. I’d heard of the practice in traditional societies, but it had always been one of those concepts I’d thought about in passing and tabled for another time. The idea has been on my mind ever since that exchange.

On the one hand, how more fundamental can it get than ingesting earth – the very source of sustenance (in one way or another)? There’s minerals, probiotics [11], and all manner of goodies to be had. On the other hand – lest we forget the more savage side of ecology – there are the less hospitable microbes, the more insidious creepy crawlies – (roundworm, anyone?). Though my conversation partner that day explained with pride and assurance that he obtained his dietary dirt from only the most trusted, meticulous, and local purveyor, I wondered if I could get past the Fear Factor element. He seemed so taken by its effects – the weight loss, the improved digestion, the higher energy. With some careful caveats, could it be worth eating dirt?

In truth, humans have been eating earth for as long as we’ve been around – and not just because Grok [12] didn’t have a salad spinner. Geophagy [13] has been observed throughout the world – everywhere from sub-Saharan Africa to Europe, Asia to Australia. In the U.S., geophagy has figured into the culture of various indigenous cultures and to the past (and present) of the South, where experts believe native Africans who were brought as slaves introduced the practice.

It’s not just one of collective humanity’s hobby horses either. Scientists have studied geophagy in a host of other mammals as well, including elephants, wolves, and primates. Surely, this common a practice must have some kind of adaptive element?

A recent article from Lapham’s Quarterly traced the unusual, circuitous, and sometimes unsettling practice of geophagy in human history. (Those of you who count among your passions both history and food will appreciate the publication’s summer issue [14].) From a scientific angle, our understanding of geophagy has involved its crucial distinction from pica [15], the consumption of all varieties of non-edibles like coins, hair, soap, etc. Our view has also been colored by the interplay of cultures, the character of terrain and its vegetation, and the division between scientific and traditional approaches to health.

The article traces at length the career of Alexander Humboldt, an 18th and 19th century explorer, who first noted geophagy in the native population of a South American mission he visited. The indigenous Otomacs, Humboldt noted, ate a “‘prodigious quantity’” of “‘soft, unctuous clay” (which they called poya) that they obtained from particular areas of a nearby river bank. In fact, they not only ate it but meticulously collected it for routine seasonal storage. Humboldt was both floored and disgusted. Nonetheless, he was apparently hooked from then on. In the proceeding decades, he continued to study geophagy as it was observed around the world. His research “normalized” geophagy to the extent that people learned to associate it less with abnormal psychology and more with long-standing tradition across the globe, even in regions as “civilized” as Sweden and Finland.

Fast forward a couple centuries, and we’re still digging for the physiological roots of geophagy – the why. The who is pretty clear. Experts have noted that children and pregnant/child-bearing aged women are the most likely to practice geophagy, but it’s not limited to these demographics. As for the what, geophagy related earth is generally clay rather than soil. Where? How? Those who practice geophagy as their ancestors did in the same regions are as particular as the Otomacs were in harvesting said clay. Tribal/community wisdom passed down through the generations directs them to very specific sites. Usually, the clay is gathered by digging down a number of several inches – where microbial presence is substantially diminished compared to surface soil. Sometimes it is eaten as is. Other times it is mixed with water and used as a dip for food.

But why? Theories have abounded in scientific corners. Many experts traced the phenomenon to mineral supplementation. In other words, animals and humans ate earth to benefit from the nutrition of it – particularly minerals like calcium and iron. Numerous studies exist attempting to correlate anemia and earth eating. Some show that those who eat earth tend to be more iron deficient [16], but the earth routinely eaten by some of these groups is actually high in iron [17].  More questions arise from there. Is something in the earth they eat interfering with iron absorption? Were they already deficient before they started eating earth? Which came first: the chicken or the egg? Moreover, when anemic, geophagy-practicing children in one study were given iron supplementation, they still ate the clay [18]. Is it culture then? Habit? Is it something else biological – or all of the above?

When scientists sampled earth from geophagic sites frequented by animals, they found that the earth contained only modest mineral content [19]. In another study, however, scientists carefully compared earth samples taken directly from where the animals ate (“interior” earth) with those taken at the surface/other spots at the site. The samples taken where the animals had eaten actually showed more mineral content [20]. (Now that’s a discerning palate!)

Just a few weeks ago, a meta-analysis on geophagy research [21] was published that goes a long way in honing in on the sense behind the practice. Sera Young from Cornell University and her fellow researchers analyzed more than 300 recorded observations of animal geophagy and nearly 500 of human geophagy instances. The records related to particular practices, soil content, etc. pointed to a rationale that’s been gaining momentum in the past two decades.

Instead of hunger of mineral supplementation, Young and her team found the most compelling support for geophagy as digestive protection and support. Those who engage in geophagy the most often (children and pregnant women), the researchers noted, are the most “vulnerable” to “dietary chemicals, parasites, and pathogens.” The clays routinely eaten in geophagic practice showed little overall mineral content. They did, however, have one thing in common – clay content.

The clay itself, Young and others researchers have noted, is key. Certain kinds of clay has the power to ease stomach distress. Anyone who’s taken Kaopectate (pre-2003 in the U.S. and any year elsewhere) knows this. It acts as a natural binder to relieve diarrhea and can curb acidity. Bothered by nausea (as many pregnant women are)? Plagued by pathogen-induced diarrhea? It’s little wonder people traditionally sought out clay. It offers inherent medicinal properties.

But that’s not all. Specific clay varieties can actually enhance a person’s or animal’s nutritional potential. The types of geophagic clay ingested by animals and people disable toxic anti-nutrients found in regionally available plants. The knowledge that has been handed down – or instinct that was selected for – allowed people and animals to increase the variety of their diets and likely take advantage of alternative food sources when traditional foods were scarcer during inclement weather, pest infestation, etc. Young’s examination showed that both humans and animals benefitted from geophagy’s ability to counter natural plant toxins. The analysis affirms research done by others who have observed the effect of clay varieties on various natural toxins, including the glycoalkaloids of wild potatoes (PDF [22]) or tannins in acorns [23].

Experts warn, however, that there’s an increasing danger to this traditional practice. For better and for worse, few if any of us across the globe live in Grok [12]’s world anymore. Agricultural and industrial pollutants have found their way into corners more remote than we could possibly imagine. Even soil in less industrialized countries is bearing the chemical stamp of modernity. One recent study analyzed samples of African soil that was sold for geophagic purposes [24] in various parts of Africa, Europe, and the U.S. Of particular concern to the researchers were the microbe and lead levels. Small levels of mercury and cadmium were also present.

Nonetheless, geophagy continues – in many traditional societies and in more “modern” regions where an increasing number of people are exploring geophagy’s protective and therapeutic effects. I’ve heard that some are using particular clay varieties to treat systemic cases of Candida or Crohn’s. I find the potential of traditionally eaten clays like kaolin, bentonite, and attapulgite – especially for these kinds of applications – compelling. As for obtaining pristine stores or supplements of these varieties, I’m not so won over.

Perhaps some of you in the Primal community practice or know folks who practice geophagy. Maybe you have sources – like the gentleman I met – who you know and trust. Maybe you have personal access to these kinds of clays and have the local resources to get your source thoroughly tested. That would be the way to do it, I’d say.

For the rest of us, there’s this. While it’s clear that geophagy played a role in our species’ evolution, we’re fortunate to have access to good sanitation and an infinite variety of foods that don’t require special formulations to aid digestion. I think there’s value in understanding how our ancestors lived and learned to thrive in their environments. There’s also value, however, in embracing the options we have today.

Thanks for reading, everyone. Let me know what you think. I’ll look forward to reading your thoughts.


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[8] health benefits of dirt: http://www.marksdailyapple.com/going-grubby-the-primal-benefits-of-dirt-dust-dishevelment/

[9] immune building properties of dirt consumption in children: http://www.marksdailyapple.com/primal-vaccine/

[10] connection between dirt and clinical depression in youngsters: http://www.marksdailyapple.com/monday-musings-dirt-deficit-depression-active-learning-and-thought-for-food/

[11] probiotics: http://www.marksdailyapple.com/whats-up-with-your-gut-beneficial-bacteria-and-good-digestive-health/

[12] Grok: http://www.marksdailyapple.com/about-2/who-is-grok/

[13] Geophagy: http://en.wikipedia.org/wiki/Geophagy

[14] summer issue: http://www.laphamsquarterly.org/magazine/index.php

[15] pica: http://en.wikipedia.org/wiki/Pica_%28disorder%29

[16] those who eat earth tend to be more iron deficient: http://www.ncbi.nlm.nih.gov/pubmed/9705186

[17] actually high in iron: http://www.ncbi.nlm.nih.gov/pubmed/9861377

[18] they still ate the clay: http://www.ncbi.nlm.nih.gov/pubmed/15049460

[19] the earth contained only modest mineral content: http://www.ncbi.nlm.nih.gov/pubmed/18521707

[20] actually showed more mineral content: http://www.ncbi.nlm.nih.gov/pubmed/14768816

[21] meta-analysis on geophagy research: http://www.jstor.org/pss/10.1086/659884

[22] PDF: http://deepblue.lib.umich.edu/bitstream/2027.42/44872/1/10886_2005_Article_BF01012098.pdf

[23] tannins in acorns: http://www.ncbi.nlm.nih.gov/pubmed/1989412

[24] analyzed samples of African soil that was sold for geophagic purposes: http://www.ncbi.nlm.nih.gov/pubmed/20889178

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