If animals and people are not getting much in the way of dietary minerals from dirt, what is the benefit of geophagia? A second explanation—that eating dirt is often a form of detoxification—is gaining credence.
DIRT DETOX
The idea that, in most cases, eating dirt is probably a way to get rid of toxins could explain why people and animals so often prefer claylike soils to other kinds of earth. Negatively charged clay molecules easily bind to positively charged toxins in the stomach and gut—preventing those toxins from entering the bloodstream by ferrying them through the intestines and out of the body in feces. Detoxification might also explain why some indigenous peoples prepare meals of potatoes and acorns with clay—these foods are bitter because they contain small amounts of toxins.
In the 1990s James Gilardi, executive director of the World Parrot Trust, found support for the detoxification hypothesis in one of the few experimental studies on geophagia. While observing a flock of Peruvian parrots foraging on a particular band of exposed soil along the Manu River, Gilardi noticed that the birds neglected nearby stretches of soil with far more minerals. He surmised that the parrots were not ingesting soil for minerals but rather to counteract toxic alkaloids in the seeds and unripe fruit that make up a large part of their diet. Toxins prevalent in plants (and meats) often irritate the gut. To test this idea, Gilardi fed some parrots the toxic alkaloid quinidine with and without their preferred dirt and measured how much alkaloid made it into the birds’ blood after the meal. Birds that did not consume the soil had higher levels of quinidine in their blood, whereas a side dish of dirt reduced quinidine levels in the blood by 60 percent. Researchers have shown the same benefit in chimpanzees and baboons that supplement their diets with clay.
Further evidence of dirt detox comes from studies of bats. A 2011 study in PLoS ONE asked whether Amazonian bats visit clay licks—cliff sides of exposed clay—for nutrition or detoxification. Christian Voigt of the Leibniz Institute for Zoo and Wildlife Research in Berlin and his colleagues captured bats of two different species: one that eats mostly fruit and one that eats mostly insects. If the bats were eating clay for minerals, Voigt predicted, he would find fewer fruit-eating bats at the clay licks because fruits have more dietary minerals than insects. But most of the bats he captured at the clay lick were fruit-eating bats—and many of them were pregnant or lactating. Voigt concluded that the pregnant fruit bats visited the clay licks to detox because they were eating twice as much to feed their babies, which meant twice the dose of plant toxins from unripe fruits, seeds and leaves.
Like bats, pregnant women may also eat dirt for its detoxifying properties, in addition to using dirt as a supplemental source of minerals. The first trimester of pregnancy plagues many women with nausea and vomiting, and cross-cultural studies document geophagia early in pregnancies in response to morning sickness. Women in sub-Saharan nations and in the southern U.S. have reported that they consume clay to alleviate this discomfort. Some researchers have proposed that morning sickness purges the mother of toxins that might harm the fetus. Perhaps geophagia and morning sickness work together to protect the developing fetus. Because clay can bind bacteria and viruses, it may also protect both mother and fetus from food-borne pathogens such as Escherichia coli and Vibrio cholerae.
Although the scientific community has only recently accumulated enough evidence to argue that geophagia is an adaptive behavior, people—and not just pregnant women—have used clay minerals as remedies for nausea, vomiting and diarrhea for thousands of years. In the age of modern medicine, pharmaceutical companies harnessed the binding properties of kaolin, a clay mineral, to produce Kaopectate, a drug that treats diarrhea and other digestive issues. Eventually the synthetic chemical bismuth subsalicylate—also the key ingredient in Pepto-Bismol—replaced kaolin, but the clay is still used today in other ways. Kaolin and smectite bind not only harmful toxins but also pathogens. Ranchers use clay when preparing livestock feed to inhibit toxin transmission, and some researchers have proposed harnessing clay’s pathogen-binding talents to purify water.
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15 Comments
Add CommentVery cool. We've accepted clay to cleanse the skin, why not the rest of the body? I've noticed that my green clay face masque actually tastes pretty good- maybe I'll try a dollop the next time I have a hangover :)
Reply | Report Abuse | Link to this-Caitlin
Dirt eating and mud wallowing comes natural to young children and dogs. There is two kinds of grass and the dirt around that grass that a dog will eat if its stomach is upset or it has gas build up. To rid its body from parasites, a dog will wallow in black mud - the kind that is found in swampy places. A child, most often, will seek out sandstone and smooth ash from burnt clay or coal if it has a food toxin build up. If the child cannot find the smooth ash, then they will eat a little bit of powdery sand - the kind that is most often found around creek banks, or burnt plant ask. If you accidently scorch the edges of your garden greens at dinner time, and if you notice your child eating that part first, then give them an anti-inflammatory drug.
Reply | Report Abuse | Link to thisTo correct an error in your report: Acorns and potatoes are not bitter herbs or plants. If a potato is sun burnt and has a shade of green to it, it will have a slight bitter taste and it is poisonous. The slight bitter taste tells a child and an animal not to eat it because it will harm them. Acorns have a slight bitter taste, which is not actually a bitter taste, but a tree sweet taste, which is a different sweet than sugar; the taste is caused by the tannins and quercitrin. Children and animals will eat acorns if they have an infection of some kind because it is an astringent with anti-inflammatory and antiseptic properties. If a child has an infection somewhere in its body, an acorn will not taste bitter to it, but have a slight sweet taste. If a child takes a bite of the acorn and it tastes sweet, the child will chew that part and swallow it. When the child takes another bite, the acorn will taste bitter and the child will spat it out. That is how nature protects us. It is good to see that science is catching up with the common person's knowledge and understanding of the world around us.
Many Americans are unnaturally obsessed with over cleanliness and "purity." This can be seen in the over use of anti-bacterial soaps to the over purification of foods.
Reply | Report Abuse | Link to thisHygiene and being clean is one thing, but being obsessively concerned with it is counter productive yet very common.
In Denmark we have an old saying "You need seven pounds of dirt a year", this article seems to validate this old adage, and explain why pregnant women sometimes eat dirt.
Reply | Report Abuse | Link to thisAt the same time, studies point to excessive cleanliness, not living with animals etc. as a possible cause of allergies etc.
In India this mud eating is a common practise amongst pregnat women.Even the local shops selling traditional medicines(called as "Pasarewale"s shop")do sell this dried mud for them. Usually this is heated in the source of heat(Shegadi) before eating(I think to get rid of germs)
Reply | Report Abuse | Link to thisMud eating is a natural response to get sufficient iron and other minerals.Like the cats who eat leafs of certain plants when they are ill.As a pregnant woman requires extra supply of these elements body demands in this form of response.Children develope a habit of eating chalks or earthen pencils when their body demands extra calcium or iron.
Reply | Report Abuse | Link to thisThe studies by Gilardi on geophagia among parrots did not explore the possibility that, although the particular clays they consume may not have been rich sources of "minerals" in general, whatever that means, or not as rich as other nearby clays, there might be a particular trace element (or two) they need that is present in higher concentration in the preferred clay. Although clays may very well reduce the blood level of quinidine when fed to parrots administered quinidine, there is some question in my mind as to how good a model this is. I want to know what the actual typical levels of assorted alkaloids are in the wild parrot diet, as well as how toxic these various alkaloid mixtures are, and I also want to know whether clay consumption varies seasonally with seasonal alkaloid level, as well as how efficacious the clay in question is at reducing alkaloid level of the real world alkaloidal mixtures. Clay eating is not universal among parrots throughout the world, and one might well wonder exactly what dietary differences exist between those which do and those which don't consume clay. What exactly is it in those particular parrots' diets that they need to be protected against that is insignificant elsewhere in the world? I'm aware that alkaloidal components are wildly varied throughout the plant world, but this explanation would make more sense if one could identify a particular toxin or group of toxins. I'd like to see a study of the alkaloidal composition of samples taken from the crops of wild parrots in the region. Are there, say, certain plant species in that region that are peculiarly toxic but that the parrots get away with consuming because of the clay eating? Show me. The possibility exists; chirimoya is a fruit that grows in the region that has toxic seeds, for instance. If you showed me that the parrots there eat chirimoya seeds and get away with it, then I would be more prone to believe Gilardi's hypothesis. But I don't buy these vague generalizations about toxins in the seeds and food they eat, as if that were a problem unique to that one area.
Reply | Report Abuse | Link to thisI grew up in the red clay hills of North Mississippi, and it was common, 50 or 60 years ago, to see people, predominantly women, take a chunk of firm red clay from the side of a road cut and proceed to eat it. These were people who appeared to be in an economic situation such that they did not receive regular medical care. A doctor once told me that he thought that they were doing this as a treatment for intestinal parasites, either to eliminate the parasites or alleviate discomfort. I assume this was what might be called a form of folk medicine.
Reply | Report Abuse | Link to thisWhile the terms "dirt" and "soil" are used synonymously in this article, soil scientists make an important distinction. Dirt is not soil. "Dirt" is what you find under your fingernails or sweep out from under your doormat. It's misplaced and is no longer part of the soil ecosystem (i.e., it's often biologically inactive or less active). "Soil" is a biologically active, living unit composed of mineral and organic materials and living forms (earthworms, microbes, etc) that performs many important ecosystem functions. We depend on soils for agricultural production, water quality and filtration, nutrient cycling, and ecosystem health.
Reply | Report Abuse | Link to thisIt may seem like semantics, but knowing the difference is important for understanding what's actually being discussed in this article.
Jennifer Ackerman's article "How Bacteria in Our Bodies Protect Our Health" in this (June 2012) issue argues that bacteria are a necessary part of human biology, helping us to perform many vital functions. Could geophagia perhaps be a mechanism by which the organism seeks to source the bacteria needed to form the microbiome and support these functions?
Reply | Report Abuse | Link to thisIn Germany "Heilerde" (i.e. healing earth or healing clay) is widely sold as alternative medicine - both for external and internal use. Its internal use is aimed to cure diseases such as diarrhea and gastroesophageal reflux. E.g. on the website of the company Luvos, which manufactures "Heilerde", one can see a person drinking this sort of clay dispersed is a glass of water.
Reply | Report Abuse | Link to thisFurthermore, the positive effects of "Heilerde" have been documented since medieval times under the names of "bolus armenicus", "terra armena", or "terra armenia". In the 19th century its use was
then publicized by the founders of the naturopathic medicine movement, e.g. Sebastian Kneipp, the "Lehmpfarrer" (clay priest) Emanuel Felke, and Adolf Just. According to Adolf Just this clay is nature's best medicine.
Now let me ask: Why were these circumstances not mentioned in the article?
Pregnant Australian Aboriginal women used to eat soil from termite mounds as it was very rich in Calcium. By the way, I remember a TV ad in England in the 60s trying to baffle the public with science in selling their indigestion tablets, showing the chemical symbols of the ingredients; Aluminium silicate (clay), Calcium carbonate (chalk), which could also be dug up from the ground where I lived (actually the chalk in the ground was Calcium bicarbonate).
Reply | Report Abuse | Link to thisIn reply to ParrotSlave - I agree with your points about toxins and lots of good questions. Have a look here at a new paper on this exact question about toxins in parrot diets (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0038293)
Reply | Report Abuse | Link to thisGood question, but unlikely to be the case - most animals, including humans, that eat soil do so well below the surface, often from a steep bank, river bank, road cut, or deep hole or cave. These sites tend to be 'soils' with high clay content, little organic matter, and little biological activity of the sort which would contribute microbial or probiotic factors to the consumers' gut.
Reply | Report Abuse | Link to thisI hope the authors check these comments, particularly Prof. Starks. A fellow faculty member at Tufts, Dr. Joel Weinstock MD, carries on lab research that deliberately introduces parasitic worms to modify or eliminate the effects of auto-immune syndromes such as Crohn's disease. While Prof. Starks and his co-author warn against ingesting "parasitic worms", the chemical/mineral approach on which they focus in their article is not sufficient to encompass all the dynamics of geophagia. It is conceivable, given Dr. Weinstock's research and that performed by the NHS in the UK amongst others, that human and animal dirt-eaters may be seeking instinctively to ingest biological life forms that could provide essential chemicals or perform other processes that help keep their immune systems in balance. The absence of certain so-called parasites may in fact be compromising the immune responses of increasing numbers of people, according to what is commonly termed the "hygiene hypothesis". I hope that the authors are prepared to reach out across disciplinary boundaries to contribute to a combination of chemical, biological, medical and social research strategies. Such a multi-pronged approach will be needed to develop a holistic public health response that could benefit those suffering from auto-immune syndromes ranging from asthma to multiple sclerosis, as well as those with diseases such as type-1 diabetes that may respond favourably to the introduction of specific parasites, microbes or chemicals. This is a major opportunity for scientists to consult together and combine resources in order to offer potentially significant benefits to a large number of people while benefitting the public health of the general population.
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