“Geophagy is the practice of eating earthy or soil-like substances such as clay, and chalk, in order to obtain essential nutrients such as sulfur and phosphorus from the soil. It is closely related to pica, a classified eating disorder in the DSM-IV characterized by abnormal cravings for nonfood items. The many possible health benefits of geophagy remain under study and are much debated. Many scientists believe that it is only harmful, while others argue that there may be adaptive benefits to the practice, since humans and animals alike have engaged in it for thousands of years.”

‘In Haiti, where three-quarters of the population earns less than $2 a day and one in five children is chronically malnourished, the one business booming amid all the gloom is the selling of patties made of mud, oil and sugar, typically consumed only by the most destitute. “It’s salty and it has butter and you don’t know you’re eating dirt,” said Olwich Louis Jeune, 24, who has taken to eating them more often in recent months. “It makes your stomach quiet down.”’

Across Globe, Empty Bellies Bring Rising Anger
BY Marc Lacey  /  April 18, 2008

PORT-AU-PRINCE, Haiti — Hunger bashed in the front gate of Haiti’s presidential palace. Hunger poured onto the streets, burning tires and taking on soldiers and the police. Hunger sent the country’s prime minister packing. Haiti’s hunger, that burn in the belly that so many here feel, has become fiercer than ever in recent days as global food prices spiral out of reach, spiking as much as 45 percent since the end of 2006 and turning Haitian staples like beans, corn and rice into closely guarded treasures.

Saint Louis Meriska’s children ate two spoonfuls of rice apiece as their only meal recently and then went without any food the following day. His eyes downcast, his own stomach empty, the unemployed father said forlornly, “They look at me and say, ‘Papa, I’m hungry,’ and I have to look away. It’s humiliating and it makes you angry.”

That anger is palpable across the globe. The food crisis is not only being felt among the poor but is also eroding the gains of the working and middle classes, sowing volatile levels of discontent and putting new pressures on fragile governments. In Cairo, the military is being put to work baking bread as rising food prices threaten to become the spark that ignites wider anger at a repressive government. In Burkina Faso and other parts of sub-Saharan Africa, food riots are breaking out as never before. In reasonably prosperous Malaysia, the ruling coalition was nearly ousted by voters who cited food and fuel price increases as their main concerns. “It’s the worst crisis of its kind in more than 30 years,” said Jeffrey D. Sachs, the economist and special adviser to the United Nations secretary general, Ban Ki-moon. “It’s a big deal and it’s obviously threatening a lot of governments. There are a number of governments on the ropes, and I think there’s more political fallout to come.”

Indeed, as it roils developing nations, the spike in commodity prices — the biggest since the Nixon administration — has pitted the globe’s poorer south against the relatively wealthy north, adding to demands for reform of rich nations’ farm and environmental policies. But experts say there are few quick fixes to a crisis tied to so many factors, from strong demand for food from emerging economies like China’s to rising oil prices to the diversion of food resources to make biofuels. There are no scripts on how to handle the crisis, either. In Asia, governments are putting in place measures to limit hoarding of rice after some shoppers panicked at price increases and bought up everything they could. Even in Thailand, which produces 10 million more tons of rice than it consumes and is the world’s largest rice exporter, supermarkets have placed signs limiting the amount of rice shoppers are allowed to purchase. But there is also plenty of nervousness and confusion about how best to proceed and just how bad the impact may ultimately be, particularly as already strapped governments struggle to keep up their food subsidies.

‘Scandalous Storm’
“This is a perfect storm,” President Elías Antonio Saca of El Salvador said Wednesday at the World Economic Forum on Latin America in Cancún, Mexico. “How long can we withstand the situation? We have to feed our people, and commodities are becoming scarce. This scandalous storm might become a hurricane that could upset not only our economies but also the stability of our countries.” In Asia, if Prime Minister Abdullah Ahmad Badawi of Malaysia steps down, which is looking increasingly likely amid postelection turmoil within his party, he may be that region’s first high- profile political casualty of fuel and food price inflation. In Indonesia, fearing protests, the government recently revised its 2008 budget, increasing the amount it will spend on food subsidies by about $280 million. “The biggest concern is food riots,” said H.S. Dillon, a former adviser to Indonesia’s Ministry of Agriculture. Referring to small but widespread protests touched off by a rise in soybean prices in January, he said, “It has happened in the past and can happen again.”

Last month in Senegal, one of Africa’s oldest and most stable democracies, police in riot gear beat and used tear gas against people protesting high food prices and later raided a television station that broadcast images of the event. Many Senegalese have expressed anger at President Abdoulaye Wade for spending lavishly on roads and five-star hotels for an Islamic summit meeting last month while many people are unable to afford rice or fish. “Why are these riots happening?” asked Arif Husain, senior food security analyst at the World Food Program, which has issued urgent appeals for donations. “The human instinct is to survive, and people are going to do no matter what to survive. And if you’re hungry you get angry quicker.”

Leaders who ignore the rage do so at their own risk. President René Préval of Haiti appeared to taunt the populace as the chorus of complaints about la vie chère — the expensive life — grew. He said if Haitians could afford cellphones, which many do carry, they should be able to feed their families. “If there is a protest against the rising prices,” he said, “come get me at the palace and I will demonstrate with you.”

When they came, filled with rage and by the thousands, he huddled inside and his presidential guards, with United Nations peacekeeping troops, rebuffed them. Within days, opposition lawmakers had voted out Mr. Préval’s prime minister, Jacques-Édouard Alexis, forcing him to reconstitute his government. Fragile in even the best of times, Haiti’s population and politics are now both simmering. “Why were we surprised?” asked Patrick Élie, a Haitian political activist who followed the food riots in Africa earlier in the year and feared they might come to Haiti. “When something is coming your way all the way from Burkina Faso you should see it coming. What we had was like a can of gasoline that the government left for someone to light a match to it.”

Dwindling Menus
The rising prices are altering menus, and not for the better. In India, people are scrimping on milk for their children. Daily bowls of dal are getting thinner, as a bag of lentils is stretched across a few more meals. Maninder Chand, an auto-rickshaw driver in New Delhi, said his family had given up eating meat altogether for the last several weeks. Another rickshaw driver, Ravinder Kumar Gupta, said his wife had stopped seasoning their daily lentils, their chief source of protein, with the usual onion and spices because the price of cooking oil was now out of reach. These days, they eat bowls of watery, tasteless dal, seasoned only with salt.

Down Cairo’s Hafziyah Street, peddlers selling food from behind wood carts bark out their prices. But few customers can afford their fish or chicken, which bake in the hot sun. Food prices have doubled in two months. Ahmed Abul Gheit, 25, sat on a cheap, stained wooden chair by his own pile of rotting tomatoes. “We can’t even find food,” he said, looking over at his friend Sobhy Abdullah, 50. Then raising his hands toward the sky, as if in prayer, he said, “May God take the guy I have in mind.” Mr. Abdullah nodded, knowing full well that the “guy” was President Hosni Mubarak.

The government’s ability to address the crisis is limited, however. It already spends more on subsidies, including gasoline and bread, than on education and health combined. “If all the people rise, then the government will resolve this,” said Raisa Fikry, 50, whose husband receives a pension equal to about $83 a month, as she shopped for vegetables. “But everyone has to rise together. People get scared. But we will all have to rise together.” It is the kind of talk that has prompted the government to treat its economic woes as a security threat, dispatching riot forces with a strict warning that anyone who takes to the streets will be dealt with harshly.

Niger does not need to be reminded that hungry citizens overthrow governments. The country’s first postcolonial president, Hamani Diori, was toppled amid allegations of rampant corruption in 1974 as millions starved during a drought. More recently, in 2005, it was mass protests in Niamey, the Nigerien capital, that made the government sit up and take notice of that year’s food crisis, which was caused by a complex mix of poor rains, locust infestation and market manipulation by traders. “As a result of that experience the government created a cabinet-level ministry to deal with the high cost of living,” said Moustapha Kadi, an activist who helped organize marches in 2005. “So when prices went up this year the government acted quickly to remove tariffs on rice, which everyone eats. That quick action has kept people from taking to the streets.”

The Poor Eat Mud
In Haiti, where three-quarters of the population earns less than $2 a day and one in five children is chronically malnourished, the one business booming amid all the gloom is the selling of patties made of mud, oil and sugar, typically consumed only by the most destitute. “It’s salty and it has butter and you don’t know you’re eating dirt,” said Olwich Louis Jeune, 24, who has taken to eating them more often in recent months. “It makes your stomach quiet down.”

But the grumbling in Haiti these days is no longer confined to the stomach. It is now spray-painted on walls of the capital and shouted by demonstrators. In recent days, Mr. Préval has patched together a response, using international aid money and price reductions by importers to cut the price of a sack of rice by about 15 percent. He has also trimmed the salaries of some top officials. But those are considered temporary measures. Real solutions will take years. Haiti, its agriculture industry in shambles, needs to better feed itself. Outside investment is the key, although that requires stability, not the sort of widespread looting and violence that the Haitian food riots have fostered.

Meanwhile, most of the poorest of the poor suffer silently, too weak for activism or too busy raising the next generation of hungry. In the sprawling slum of Haiti’s Cité Soleil, Placide Simone, 29, offered one of her five offspring to a stranger. “Take one,” she said, cradling a listless baby and motioning toward four rail-thin toddlers, none of whom had eaten that day. “You pick. Just feed them.”

{Reporting was contributed by Lydia Polgreen from Niamey, Niger, Michael Slackman from Cairo, Somini Sengupta from New Delhi, Thomas Fuller from Bangkok and Peter Gelling from Jakarta, Indonesia.}

posted by DloPwop , April 18, 2008

“I live in Haiti, and when I find news about Haiti it’s often some variation on the story “people in Haiti are so poor they eat dirt”. I think it may be more complex than that. I live in an area that is poor, but not especially poor by Haiti standards. The vendors selling candy on the side of the road will often have a stack of mud cakes next to the candy, and I have seen children choosing to buy them instead of candy – very odd. Apparently, only a particular kind of fine-grained clay is used, and it is mixed with butter and salt and flavored. Pregnant women especially seem to crave the mud cakes. I theorize that there are minerals in the mud that Haitians aren’t getting from the standard rice and beans diet. I’m not saying that the statement “Haitians are so poor, they have to eat dirt” is 100% false, but I don’t think poverty is the only reason for this. No, I haven’t tried eating one yet.”



8.2 Dirt As Food / Pica / Geophagy

Known variously as pica or geophagy, eating soil is widespread among many animals on every continent. It is also frequently observed among people, especially traditional societies. In wild animals, eating dirt seems to be a weapon inthe ancient competition between plants and animals. Geophagy is an animal weapon in the struggle between plant reproduction strategy and the animal desire for food.

A way of understanding geophagy is to consider the strategies involved. Many plants use animal mobility to spread seeds by enticing animals with tasty fruit. The animal digests the pulp, but spits out the seed or passes it unharmed through its digestive system to be defecated–freshly potted and fertilized. Plants fend off the animals by discouraging consumption until the seeds are ready to sprout by making the pulp bad tasting or even poisonous. Plants manipulate us by making us wait until the pulp of fruit is suitable to eat–and the seeds are ready for dispersal.

Seeds possess a concentrated supply of carbohydrates, proteins, and fats to help them germinate and grow. Bad tastes or poisons are added to the seeds–or unripe fruit–to fend off animals. How to overcome them? Parrots will eat soils containing minerals that bind plant toxins effectively. In fact, they are quite selective in choosing the most effective soils for their purpose. (My comment: parrots are very intelligent creatures. Some have learned to speak and understand over a hundred English words. Trial and error seems to be part of their behavioral repertoire in nature.)

Are you acquainted with the place name ‘lick’ such as French Lick in southern Indiana? It is a place where animals gather to eat soil. North American wild hoofed animals visit licks, as do bears and many small mammals. Feeding selected soils to cows, sheep, goats and pigs results in enhanced growth–by 20% or more.

Antler-growing deer eat soil rich in calcium and magnesium. Some animals seek out sodium. So, with animals (and humans), in some cases a particular element is sought. The most compelling need, however, seems to be the need to detoxify plant products in the diet.



People seem to use geophagy to protect themselves against plant toxins. We are accustomed to eating domesticated potatoes. In South America, however, some Indians regularly eat bitter, toxic wild potatoes capable of producing stomach pains and vomiting. They have learned to make the potatoes safe and palatable by eating them with an alkaloid-binding clay. (My comment: we have not met plant alkaloids yet; we will see their plant kingdom distribution and medical significance when we get to rainforest pharmacology.)

California Native American Indians harvested acorns as a major staple in their diet. Before contact, they routinely burned the forest undergrowth to encourage growth of the some twenty species that they exploited in their environment. To make the acorns edible, the naturally occurring tannic acid had to be removed. This was done by soaking the whole acorns in a running stream or percolating water through ground acorn flour. Another technique was to mix the acorn flour with a clay that reduced the tannic acid content by up to 77 percent. They achieved this know-how by trial and error. We can verify its efficacy today with chemistry.

Geophagy is especially popular with pregnant and nursing mothers, who have an increased need for minerals (and mineral supplements). In Zambia and Zimbabwe the main sources of soil, which 90% of rural women consume while pregnant are giant termite mounds that also attract cows and giraffes. When asked why, they might answer “I feel good when I eat it” or “I like the taste.” This doesn’t answer the question for us with a physiological perspective, but craving for trace elements may be the reason for eating–dirt!

Geophagy – Eating Dirt / A Traditional Practice Which Provides
Nutrients to the Body
BY Matt Rosenberg / filed in: Cultural Geography

People around the world eat clay, dirt or other pieces of the lithosphere for a variety of reasons. Commonly, it is a traditional cultural activity which takes place during pregnancy, religious ceremonies, or as a remedy for disease. Most people who eat dirt live in Central Africa and the Southern United States. While it is a cultural practice, it also fills a physiological need for nutrients.

In Africa, pregnant and lactating women are able to satisfy the very different nutritional needs of their bodies by eating clay. Often, the clay comes from favored clay pits and it is sold at market in a variety of sizes and with differing content of minerals. After purchase, the clays are stored in a belt-like cloth around the waist and eaten as desired and often without water. The “cravings” in pregnancy for a varied nutritional intake (during pregnancy, the body requires 20% more nutrients and 50% more during lactation) are solved by geophagy.

The clay commonly ingested in Africa contains important nutrients such as: phosphorus, potassium, magnesium, copper, zinc, manganese, and iron. The tradition of geophagy spread from Africa to the United States with slavery. A 1942 survey in Mississippi showed that…

at least 25 percent of the schoolchildren habitually ate earth. Adults, although not systematically surveyed, also consumed earth. A number of reasons were given: earth is good for you; it helps pregnant women; it tastes good; it is sour like a lemon; it tastes better if smoked in the chimney; and so on.*

Unfortunately, many African-Americans who practice geophagy (or quasi- geophagy) are eating unhealthy material such as laundry starch, ashes, chalk and lead-paint chips because of psychological need. These materials have no nutritional benefits and can lead to intestinal problems and disease. The eating of inappropriate objects and material is known as “pica.”

There are good sites for nutritional clay in the Southern United States and sometimes family and friends will send “care packages” of good earth to expectant mothers in the North. Other Americans, such as the indigenous Pomo of Northern California used dirt in their diet – they mixed it with ground acorn; this neutralized the acid.

* Hunter, John M. “Geophagy in Africa and in the United States: A Culture-Nutrition Hypothesis.” Geographical Review April 1973: 170-195. (Page 192)

BY Jared M. Diamond  /  Nature 400, 120 – 121 (1999)

As babies, we are warned by our mothers not to eat dirt, but as adults some of us do it anyway and dignify it with the name of geophagy. The regular and intentional consumption of soil, by itself or mixed with food, has been recorded from traditional human societies on all continents, especially among pregnant women1-4. Geophagy has also been documented in many species of mammals, birds, reptiles, butterflies and isopods, especially among herbivores5-9. Why do they and we do it? Proposed biological functions of geophagy have now been tested by James Gilardi and co-workers10, who uncover a fascinating evolutionary arms race between plants and their would-be animal consumers.

The dirt-eaters studied were Peruvian Amazon rainforest parrots, of which a thousand or more individuals of 21 species gather early each morning at certain sites with exposed bare soil on river banks or cliff faces. Because these sites are ideal for viewing and photography, they attract 4,000 bird-watching tourists each year, support 500 jobs in the local ecotourism industry, and earn Peru about US$1,000 per year per individual wild macaw. The birds’ taste in dirt is highly specific: for instance, they congregate not just at one particular bend of the Manu River but at one soil band running hundreds of metres horizontally along that bend, spurning the dirt in bands one metre above or below the preferred band. Gilardi et al. tested possible functions of geophagy by comparing the physical and chemical properties of soil samples from the preferred and rejected bands.

The commonest explanation for geophagy in birds is to provide grit. Because birds lack teeth, many ingest pebbles or coarse soil with which to grind food in their gizzards. Preferred particle sizes of grit increase with bird size, from 0.5 mm for sparrows to 2.5 cm for ostriches. However, Gilardi et al. found that the soil preferred by Peruvian parrots is very fine: only 5% of it by volume is coarse sand exceeding even 0.05 mm in particle diameter. Most of it is clay less than 0.2 m in particle diameter, and preferred soils contain only a quarter as much coarse sand and nearly twice as much fine clay as rejected soils. So parrots are not eating soil to get grit. On reflection, this is not surprising: parrots have no need for grit because their strong, sharp bills can shred the hardest nuts.

A second function of geophagy, suggested for livestock, wild ungulates, rabbits, butterflies and pregnant women, is to provide essential minerals6,7. Soils sold in Ghanaian markets to pregnant African women are richer in iron and copper than the dietary supplement pills made by pharmaceutical companies specifically for prenatal use. But Gilardi et al.10 found that soils preferred by parrots contain lower available quantities of most biologically significant minerals than non-preferred soils, and much lower quantities than the parrots’ preferred plant foods. Hence, unless the parrots are making a big mistake in their taste preferences, they are not selecting soils for mineral content.

A third function of geophagy, proposed for ungulate livestock, is to buffer the rumen contents6. Because parrots lack a rumen, it will come as no surprise that their preferred soils have no more buffering capacity than distilled water. What, then, do the parrots actually gain from ingested soil? It turns out that they regularly eat seeds and unripe fruits whose content of alkaloids and other toxins renders them bitter and even lethal to humans and other animals. Because many of these chemicals are positively charged in the acidic conditions found in the stomach, they bind to clay minerals bearing negatively charged cation-exchange sites. That’s why experienced tourists visiting destinations with poor sanitation carry medicines such as kaopectate (high in clay minerals) to adsorb the toxins. That’s also why peasant farmers and hunter-gatherers throughout the world often mix bitter but otherwise nutritious plant foods (like acorns and wild potatoes) with selected soils before consumption.

Peruvian parrots behave like sophisticated human tourists and hunter-gatherers. Their preferred soils were found to have a much higher cation-exchange capacity than adjacent bands of rejected soils — because they are rich in the minerals smectite, kaolin and mica. In their capacity to bind quinine and tannic acid, the preferred soils surpass the pure mineral kaolinate and surpass or approach pure bentonite. Clearly, parrots would be well qualified for jobs as mining prospectors.

Gilardi et al. confirmed this hypothesis with two sets of bioassays. First, they exposed brine shrimp (the toxicologist’s test animal of choice) to extracts of seeds routinely consumed by macaws. Many of the brine shrimp died, confirming the toxicity of the parrots’ diet. But mixing the solutions or extracts with soil preferred by parrots reduced the effective toxin loads by 60-70% and improved shrimp survival. Second, Amazon parrots were given an oral dose of the alkaloid quinidine with or without preferred soil, and quinidine levels were measured in the parrots’ blood for three hours as absorption took place from the gut. Providing soil along with the quinidine reduced absorbed quinidine blood levels by 60%.

What is the evolutionary significance of plant toxins and animal anti-toxin behaviour? From a plant’s evolutionary perspective, a seed should be high in nutrients to support germination and seedling growth; the ripe fruit around the seed should also be nutrient-rich and attractive to animals, encouraging them to pluck and eat the fruit and disperse the seed. On the other hand, the seed itself should be repulsive to animal consumers, inducing them to regurgitate or defaecate it, and the unripe fruit should be repulsive, lest animals harvest it before the seed is viable. From an animal’s evolutionary perspective, an ability to defeat the plant’s toxin defences would enable it to obtain the nutrients in the seed as well as those in the ripe fruit, and to outcompete other animal consumers by harvesting the fruit while it is unripe and still unpalatable to them.

Any textbook of animal biology describes the resulting evolutionary arms race, in which plants evolve increasingly potent toxins (such as strychnine and quinine), and animals evolve increasingly potent means of detoxification. While enzymatic detoxification has previously received the most attention, the work of Gilardi et al.10 and the wide distribution of geophagy among animal herbivores suggest an additional important means of detoxification by adsorption on ingested soil minerals.

A host of interesting questions now comes into focus. How do parrots discover the best soils — can they discriminate among soils immediately by texture and taste, or must they experiment with various soils mixed with toxic food and discover which soil assuages their upset stomach? Might the availability of suitable geophagy sites limit herbivore distributions and merit concern from conservation biologists? Only certain species of local herbivores are reported as visiting geophagy sites: why? To return to our youthful dirty habits, do curious dirt-licking babies deserve our encouragement for their experiments with self-medication?

Jared M. Diamond
email : jdiamond [at] geog [dot] ucla [dot] edu

Soil ‘ultra-bugs’ thrive on a diet of antibiotics
BY Ewen Callaway  /  03 April 2008

Call them the “ultra-bugs” – bacteria that are not merely resistant to antibiotics, but feed on them. They lurk in dirt from parks, farms and gardens. While the ultra-bugs don’t normally cause disease, researchers are concerned the bacteria might pass drug resistance onto their deadly kin. Unlike antibiotic-resistant bacteria, such as MRSA and XDR tuberculosis, which grow on other food in the presence of the drugs, the soil bacteria can subsist on a diet of antibiotics alone. The ability is akin to a person thriving on a diet of snake venom.

While hunting for soil bacteria that can turn plant waste to biofuels, a team of microbiologists led by George Church of Harvard University, Boston, Massachusetts, decided to grow soil samples in pure antibiotics as a control. “We expected not to find a lot of bacteria that could eat antibiotics for breakfast,” says Church. “We were kind of surprised.”

Multiple resistance
To make sure the discovery was not a fluke, his team collected more dirt from farms, forests and parks around the northeast United States and Minnesota. All the soil samples contained bacteria that can survive on antibiotics, and many subsisted on multiple drugs, he says. Not only could the soil bacteria live on older antibiotics that many bacteria have developed resistance to, such as penicillin, but they could digest modern-day silver bullets as well, including ciprofloxacin.

Many of the bacteria were found to be impervious to the bulk of antibiotics, although they often could not grow without alternative food sources. “They are resistant to virtually all antibiotics,” says microbiologist Morten Sommer, also at Harvard. Among 75 strains the team tested, half were resistant to clinical doses of 17 of 18 antibiotics. That trait is particularly worrisome, says Sommer. Though none of the bacteria normally cause human disease, many are close relatives of pathogenic strains.

Spreading genes
For instance, Church’s team found numerous species of Pseudomonas bacteria, relatives of a microbe that infects people with cystic fibrosis and burns. And two-fifths of the bugs isolated were related to Burkholderia, a pathogen considered a potential bioterror weapon. The soil bacteria could pass the genes for antibiotic resistance and metabolism onto pathogens, says Church. In unpublished experiments, he found that the bugs can spread drug resistance to harmless lab strains of E. coli. “If the genes are out there to metabolise these wonder drugs, I think that’s something we should be aware of and be cautious of,” says Gerry Wright, a microbiologist at McMaster University in Hamilton, Ontario, Canada. He suspects that much of the antibiotic resistance seen in hospitals originates in soil.

But the finding also offers reason for optimism, says Stuart Levy, a microbiologist at Tufts University in Boston. Soil bacteria have been locked in a bioweapons arms race for billions of years, and have developed the ability to feed on each others naturally occurring antibiotics. If you take these bacteria into the lab and stop them from eating each other’s weapons, says Levy, levels of these novel antibiotics should build up, and we may be able to extract them for clinical use.

Journal reference: Science (DOI: 10.1126/science.1155157)



BY Gerald N. Callahan  /  2003 Aug

This earth is blessed
Do not play in it

–  Sign on the wall of El Santuario de Chimayo, New Mexico

This place feels old beyond human recollection. The carvings and paintings were surely done by human hands, but no one remembers whose hands those were. The work is striking, especially in the apse behind the altar. There, the colors of surrounding hills have been transferred onto nearly luminous wooden reredos full of Catholic symbolism. Above the altar hangs a most intricate ancient Christ crucified on a green cross. Overhead, the roof is held in place by massive carved wooden beams, big around as human bodies and blackened by nearly two centuries of incense and candle smoke. The air is rich with the memory of thousands of benedictions and baptisms.

Threadbare trousers have polished the pews to a high varnish that this afternoon ripples with a low orange glow from dozens of votive candles burning purposefully in back of the church. This is El Santuario de Chimayo, an old adobe-brick and stucco structure in the hills of northern New Mexico. This chapel was built in 1816, but a sanctuary has been at this site for much longer. The locals offer many legends about its origins, fanciful tales of miraculous crucifixes and Santo Niños. But the truth is buried beneath the murk of time. One thing is clear though, as beautiful as the sanctuary is and as striking as the crucifix (El Sefior de Esquipalas) above the altar is, nearly none of those in the pews today have come to see the sanctuary or the crucifix. Instead, they have come from all over the world to this place in New Mexico to eat the dirt that lies beneath the adobe floor.

According to legend, that dirt is sacred, consecrated by Christ himself. Crutches cast off by the newly healed fill the anteroom, and on some days, the line of pilgrims stretches for blocks. Some call this place the Lourdes of America, but in Chimayo the miracle can be seen each day by anyone who peers into a low-ceilinged room off the main entrance. There, a hole (the posito), half a meter across, pierces the floor. Beside it, someone has left a plastic spoon to aid the faithful. Beyond the spoon, beneath the opening, lies only dirt, only the deep-red dirt of Chimayo.

Most of the faithful here today have come to eat that dirt. This religious tradition is practiced, as far as I know, only at one other place—a Catholic shrine in Esquipalas, Guatemala. But pilgrims to these shrines are not the only humans who eat dirt. Nor are religious reasons the only reasons to imagine that dirt may have special powers.

Geophagy (Eating Dirt) and Its Reasons
Other than water, what little stuff we humans have inside us is largely dirt. Admittedly, this dirt is sometimes highly processed before we receive it, but most solids that make up humans and other creatures either are now or recently were dirt (the simple stuff that stripes the outer surface of our world, the thin paste that raises us above rocks) transformed by sunlight into plants or animals. Most of us prefer the dirt we eat in the form of cows and sheep and carrots and squash and bison and sorghum. Other dirt we’d just as soon scrape from our feet and leave at the door.

But not everyone wishes to be so far removed from the stuff of mud pies and mucilage. On every continent (except, possibly, Antarctica), some of us intentionally eat dirt, and we are joined in this practice by a myriad of rats, mice, mule deer, birds, elephants, African buffalo, cattle, tapirs, pacas, and several species of primates (1). Most scientists consider animal geophagy “normal,” probably because most soil consumption by animals has no obvious adverse effects and is sometimes beneficial (2); however, some of these same scientists consider most (or all) human geophagy “abnormal.”

Abnormal Behavior
In the United States, many of us believe that humans should only eat food. We consider the consumption of nonfood items pathological, even though we know that what people define as “food” varies dramatically by region and ethnicity. We call the pathological act of eating nonfood items pica. Pica is a disease, but a disease different from polio or smallpox. No infectious agent is obviously associated with pica. Pica is a disease only because we believe normal “undiseased” persons would not eat anything but traditional human foods; some of those who do, some of the time, are at considerable risk because of their unusual appetites.

Pathological consumption of soil, “soil pica,” is associated with several psychological abnormalities. But all ingestion of soil is not soil pica. How much soil a person has to eat to be considered ill is not known. One report described soil pica in a developmentally disabled person who regularly consumed more than 50 g of soil per day (3). Most of us would consider that level of geophagy at least potentially pathological, although I am not sure why.

In June 2000, the U.S. Agency for Toxic Substances and Disease Registry appointed a committee to review soil pica. The committee settled on pathological levels as consumption of more than 500 mg of soil per day but conceded that the amount selected was arbitrary (3). Soil consumption is defined as pathological according to the amount eaten (no normal person could possibly eat that much dirt) and the severity of health consequences (lead poisoning, parasites). Because underlying psychological or biologic abnormalities are not easy to establish, I explore only what appears to be nonpathological dirt eating in pregnant women (especially in sub-Saharan Africa), migrants from sub-Saharan cultures to other parts of the world (notably the United States), and children worldwide.

Inadvertent Exposure
Why is it, that in spite of all the times we’ve been told not to, we still eat dirt? This is a very complex question with many possible answers. And while each proposed answer has its advocates, no single answer seems satisfactory to all—except one. Almost everyone agrees on one cause of geophagy, inadvertent consumption of air-, water-, and foodborne dirt. Contaminated food, soiled hands, and inhaled dust add soil to our diets. Children ingest considerable amounts of soil in these ways. My children did. Of course, my children also ate dirt on purpose. But child or adult, each of us inadvertently eats a little dirt every day. This dirt can pose a health threat, especially near sites of industrial contamination, but dirt we eat intentionally poses a greater challenge. Intention may indicate something biologic that drives some of us (sometimes regularly, sometimes religiously, sometimes ritually) to eat dirt.

Tradition and Culture
For centuries, indigenous peoples have routinely used clays (decomposed rock, silica and aluminum or magnesium salts, absorbed organic materials) in food preparation. The clays were used to remove toxins (e.g., in aboriginal acorn breads); as condiments or spices (in the Philippines, New Guinea, Costa Rica, Guatemala, the Amazon and Orinoco basins of South America); and as food during famine (4). Clays were also often used in medications (e.g., kaolin clay in Kaopectate). But the most common occasion for eating dirt in many societies (the only occasion in some societies) is pregnancy. When sperm and egg collide, the world changes. That is obvious. But why pregnant women eat dirt is not.

Wiley and Katz (5) have proposed that eating clay serves different purposes during different periods of pregnancy, soothing stomach upset during morning sickness in the first trimester and supplementing nutrients (especially calcium) during the second and third trimesters, when the fetal skeleton is forming. This type of geophagy occurs most commonly in cultures of sub-Saharan Africa and their descendants (5). The timing of dirt ingestion and amounts consumed vary with tribes and individual persons, but soil comes consistently from certain sites. In some cultures, well-established trade routes and clay traders make rural clays available for geophagy even in urban settings. Clays from termite mounds are especially popular among traded clays, perhaps because they are rich in calcium (5). Whatever the underlying reason, geophagy in Africa does not appear to be a recent cultural development; it may predate Homo sapiens.

Women eat dirt during the first, second, or third trimester or throughout pregnancy (5), often throughout the day, as a supplement rather than a meal. Most commonly consumed are subsurface clays, especially kaolin and montmorillonite (5), 30 g to 50 g a day (sometimes much more) (3). However, eating dirt is not always confined to pregnant women, even among the cultures of sub-Saharan Africa (4), nor is it limited to tribes with little or no access to dairy-derived calcium (5), so these hypotheses do not adequately explain local tastes for dirt.

Soil, including kaolinitic and montmorillonitic clays, contains considerable amounts of organic material, including many live microorganisms. The human gut is the largest area of direct contact between a person and the world. Gut-associated lymphoid tissue (GALT) is a major site of T-cell differentiation and selection in adults and of intense immunologic activity (including T lymphopoiesis) in children and adults (6–9). And while it is not entirely clear why some gut-introduced antigens promote tolerance of microorganisms and others immunize against them (10), it is clear that immunization via the gut is a major source of immunoglobulin (Ig) A, both locally and systemically (6–10).

Regular consumption of soil might boost the mother’s secretory immune system. Monkeys that regularly eat dirt have lower parasite loads (1). In some cultures, clays are baked before they are eaten, which could boost immunity from previous exposures. For decades we have used aluminum salts, like those found in clays, as adjuvants in human and animal vaccines. Adjuvants are compounds that nonspecifically amplify immune response, probably because of their effects on innate defenses such as macrophages, dendritic cells, and the inflammatory response. Aluminum compounds make effective adjuvants because they are relatively nontoxic, the charged surfaces of aluminum salts absorb large numbers of organic molecules, and macrophages and dendritic cells readily phagocytose the particulates produced by the combination of the adjuvants and the organic compounds (11). The clays that pregnant women and others consume, which are rich in aluminum compounds, likely make at least passable immunologic adjuvants. For all these reasons, clays might act as vaccines. And the IgA antibodies produced against the associated organic antigens may appear in breast milk and have a major role in mucosal protection of newborns.

In pregnant women, this type of gut immunization might produce high levels of IgA against endemic pathogens and other antigens. All this IgA would appear shortly before birth in the breast milk and would provide protection for infants against precisely the pathogens encountered immediately after birth. Furthermore, IgA antibodies prevent attachment of bacteria and some viruses at mucosal surfaces (12), the major contact between the infant and the infectious world. In humans, mucosal surfaces offer the only routes of natural immunization short of wounding, and dirt would seem to offer a potent vaccine containing many endemic pathogens—no needles, no sugar-cube, no gene gun.

Eating dirt, then, rather than being abnormal, may be an evolutionary adaptation acquired over millennia of productive and not-so-productive interactions with bacteria—an adaptation that enhances fetal immunity and increases calcium, eliminates gastric upset, detoxifies some plant and animal toxins, and perhaps boosts mothers’ immunity at times when the hormones of pregnancy (13), factors produced by the fetus (14), changes in the complement system, replacement of MHC class I antigens in the trophoblast (15), and who knows what else suppress the mother’s natural immunologic desire to destroy her fetus—a miracle, nearly.

Innate Tendency
My children ate dirt with surprising gusto, garden soil, road soil, leaf-mush soil, sod soil, bug-body soil—even gutter soil. As usual with my children, before I could talk them out of this behavior, they gave it up on their own—their behavior depending more on personal likes and dislikes than on my paternal concerns. I was pleased when they quit. Later I was reassured to discover from other parents that their children were just as taken with dirt as mine, some even more so. I felt less like the parent of a couple of dirt-eating, psychosis-ridden, nutritionally deprived children, even if my children were never quite “normal.”

Eating dirt appears nearly universal among children under 2 years of age. When I asked my 2-year-old daughter why she ate dirt, she just stared at me, her eyes wide open, a thick moustache of loam limning her lips. She must have decided that either what I had asked was unfathomably abstract or her answer would be far beyond my comprehension.

Soil pica has been defined as eating 500 mg to >50 g of soil per day (3). But the general applicability of these numbers is widely disputed (pregnant women in Africa eat far more soil than this). By inference, however, normal soil consumption must fall into the range of 0 mg to 500 mg per day per small mouth. Soils consumed by children may differ from those consumed by adults. Generally, children consume topsoils and not the deep (60 cm- to 90-cm deep) clays adults regularly consume (5). And children are considerably less selective in the sites they choose for dirt to eat. But why children eat dirt remains largely obscure to all but children.

Children may eat soil for the same reasons pregnant women and some animals do (2,4,16–18). Because of their rapid growth, they have special nutritional needs and surface soils may serve as supplemental nutrients; detoxification of plant or animal toxins might be accelerated by geophagy— particularly in some parts of the world; or soil components, especially clays, may relieve gastric distress. But topsoils are probably not as effective as deep clays at gastric soothing.

Among children, too, it seems eating dirt might have immunologic consequences. Maternal immunoglobulins are secreted in breast milk shortly before birth and for 1 year or more afterwards. Children often begin eating dirt a year or two after birth. As maternal immunity wanes, eating dirt might “vaccinate” children who are losing their maternal IgA, which could stimulate production of nascent immunoglobulins, especially IgA. Eating dirt might also help populate intestinal flora.

But all of this remains speculative. No clear evidence supports a biologic benefit to geophagy among children. Its frequency and distribution, though, suggest a greater biologic involvement than the simple oral obsessions of children.

Risks of Eating Dirt
How dangerous is eating dirt? My mother was pretty certain about this— damn dangerous. Soils contaminated by industrial or human pollutants pose considerable threat to anyone who eats them. Reports abound of lead poisoning and other toxicities in children eating contaminated soils. Similarly, we do not have to look farther than the last refugee camp or the slums of Calcutta or Tijuana or Basra to find the dangers of soils contaminated with untreated human waste. But the inherent biologic danger of soil is difficult to assess. Soil unaffected by the pressures of overpopulation, industry, and agriculture may be vastly different from the soil most of us encounter routinely.

Using DNA-hybridization analyses, Torsvik et al. (19,20) found an estimated 4,600 species of prokaryotic microorganisms per gram of natural soil. Subsequent investigations, using more sophisticated techniques, found even more species (20), 700–7,000 g of biomass per cubic meter of soil. Soil is a considerable biologic sink, and certainly some organisms found in it are pathogenic in humans. Yet evidence of soil as a major cause of disease in humans and other animals is limited. And many reported diseases are the result of an abnormal situation, e.g., industrial pollution or untreated sewage.

Most infectious diseases acquired through eating dirt are associated with childhood geophagy, which routinely involves topsoils rather than deep clays. One recent report describes infection of two children at separate sites with raccoon roundworm (Baylisascaris procyonis ) (21). The infection resulted in severe neurologic damage to both children, and one died. The roundworm was ingested along with soil in both cases. Eating dirt can have dire consequences.

In the United States, the most common parasitic infection associated with geophagy is toxocariasis, most often caused by the worm Toxocara canis. Seroprevalence is 4% to 8% depending on the region, but incidence of antibodies to T. canis is as high as 16%–30% among blacks and Hispanics. The most common route of infection is ingestion of soil contaminated with dog or cat feces (22). Even though, humans are only paratenic hosts of T. canis, under some circumstances (though severe cases are rare), the worm can cause considerable damage (visceral larva migrans, ocular larva migrans, urticaria, pulmonary nodules, hepatic and lymphatic visceral larva migrans, arthralgias) (22–24). Toxocara eggs persist in soil for years. As with soils contaminated by human wastes, soil consumption itself does not cause toxocariasis. And studies of seroprevalence do not distinguish between infection and immunization.

Among children in Nigeria, the most common parasitic infection associated with eating dirt is ascariasis (25). Ascarid worms infect as many as 25% of the world’s population (more than 1.25 billion). A scaris lumbricoides is the most common worm. Asymptomatic in many adults, infection is much more serious in children; intestinal obstruction is the most common symptom. Because the worms do not replicate in humans, reexposure is required to maintain infection beyond 2 years. The correlation between geophagy and helminth infection varies with different helminthes. Geissler et al. reported correlation between geophagy and ascariasis (especially caused by A. lumbricoides) and possibly trichuriasis but none between geophagy and reinfection with Schistosoma mansoni, Trichuris trichiura, or hookworm (26). All parasites that infest soil do not uniformly infect people who consume dirt. Nor do all who eat dirt routinely contract disease.

Immunologic Development and Infectious Disease
Many nonhuman animals regularly eat dirt, generally without ill effects and in many cases with some benefits. Even in humans, there are few reports of infections routinely associated with geophagy by pregnant women in sub-Saharan Africa, probably because women take clays from 60 cm to 90 cm below the soil surface and, at least some of the time, they bake the clays. But these factors seem inadequate to fully account for the frequent absence of overt ill effects.

Helminth infections associated with geophagy appear to affect the frequency of inflammatory bowel diseases, which occur most often in industrialized nations. The underlying cause of these diseases may be abnormal immune response to the contents of the gut or perhaps to the gut itself (27). Inflammatory bowel diseases occur at much lower rates in regions where helminth infections are common. Development of normal gut-associated immune response may be aided by the presence of worms.

In studies of healthy mice, Trichinella spiralis prevented colitis induced with tri-nitrobenzene sulfonic acid by redirecting a primarily Th-1 response to a Th-2 response (28). Preliminary studies indicate that helminth infection may also alter the course of inflammatory bowel disease in humans (29). Soil is a rich source of parasitic worms. Studies using a number of other animals have also, at least indirectly, associated dirt and microorganisms with normal immunity.

The Environmental Protection Agency estimates that children in the United States consume, on average, 200–800 mg of dirt per day. Some children regularly consume more than their allotment. Still, that doesn’t seem like a lot of dirt. We parents have tried for years to put a stop to it. I don’t know of an instance in which anybody has succeeded in keeping children away from dirt. But animals have been successfully raised in absolutely sterile environments. Rabbits, mice, guinea pigs, and rats have been raised under such conditions (30,31). In each case, the immune system failed to develop normally. Lymph nodes and GALT did not achieve the right shape or composition and could not initiate normal immune response. Reexposure to infection later in life does not work, at least not fully. There is a window when infection drives the immune system toward its proper end. After that, mice, rats, rabbits, and guinea pigs are at the mercy of the microbial world.

Evidence suggests that the results would be the same in children. In large families, children with many older brothers and sisters are less likely to have asthma, hay fever, or eczema. West African children who have had measles are half as likely to have allergies as children who never had measles. Italian students who recovered from infection with hepatitis A had fewer and less severe allergies than fellow students who were never infected. Children with Type I diabetes (an autoimmune disease) are less likely to have had infections before their fifth birthdays than healthy children of the same age. Children raised in rural areas, especially on farms, have fewer allergies and autoimmune diseases than children raised in cities. All of these notions have been referred to as the “hygiene hypothesis” (32).

Children exposed a little more to the infectious face of this world seem to fare better as adults. I do not mean to say that vaccination is inappropriate. Vaccination is, most often, infection, and vaccinations have done more to improve childhood survival rates that any other single bit of modern medicine. Nor are water purification and sewage treatment inappropriate. Water and sewage treatment have done even more than vaccination to eliminate disease in areas where human populations have exceeded the ability of the local environment to deal with human waste and the pathogens associated with it. But, evidence indicates that infection early in life is critical for the development of normal immune systems.

Exposure-dependent development is not limited to the immune system. Animals, humans included, must be exposed to the sights, sounds, feels tastes, and smells of this septic world. When we are not, our nervous systems do not develop normally, do not rewire, expand, and contract as they must to survive (33). For humans, as for rabbits, there is a window in childhood when our experiences, our infections, change everything, once and for all. Inside that window, infection causes lymph nodes and GALT to enlarge and reorganize, to separate into cortices and medullae, into primary lymphoid follicles, and develop T- and B-lymphocyte–rich regions of immune competence destined to someday be germinal centers, where our defenses will muster and the real battle will be fought. This window is a defining moment, when the simplest and lowest forms of life—the dirty, the infectious, the parasitic, and the septic—alter who we are.

We do not know which childhood infections are most important, but several studies implicate mycobacterial infections. A large group of bacteria most of which cause no apparent disease, the mycobacteria, have strains that cause serious diseases (e.g., tuberculosis, leprosy). Mice injected with ovalbumin (the major protein in egg white) become allergic to ovalbumin. But mice first infected with mycobacteria and then injected with ovalbumin do not become allergic (34).

Early infection of children with some mycobacteria may promote strong immune systems, a normal sense of self, and a normal defense of that self. Mycobacteria are found in large numbers in dirt. And animals (probably including humans) kept from this dirt may lose the ability to recognize certain dangerous organisms as a threat, lose the ability to discriminate between self and not self, and lose the ability to distinguish the fatal from the innocuous.

The “Age of Bacteria”
For more than 3 billion years, microorganisms, especially bacteria, have ruled earth. As Stephen Jay Gould said, “We live now in the ‘Age of Bacteria.’ Our planet has always been in the ‘Age of Bacteria’ ever since the first fossils, bacteria of course, were entombed in rocks more than three and a half billion years ago” (35). And bacteria have done more than any other living group to alter the character of this earth (36). It has been estimated that more than 1029 bacteria live on this planet and as many as 1014 live on each one of us. Through all of history, we humans have waltzed with bacteria and the rest of the microscopic world. We had no choice. Bacteria outnumber, outweigh, out-travel, and outevolve us.

That bacteria cause so many human diseases is not astounding. It is astounding that so few bacteria cause human disease. Pathogenic bacteria are merely the microscopic tip of the largest of all biologic icebergs. How fortunate, we imagine. But fortune may have little or nothing to do with our survival. Billions of years of confrontation rather than luck were likely our benefactor. Through those confrontations and those eons, nearly all of us learned to coexist peacefully. Neither humans nor microorganisms benefit from fully destroying the other. Fatal infections seem, biologically at least, shortsighted. And even a brief course of antibiotics is enough to remind us that a world without bacteria would be a poorer world. This is not a war, as it has often been described, even though we have mustered an impressive array of weapons—bactericidal cribs and mattresses, toilet cleaners and counter tops, blankets, deodorants, shampoos, hand soaps, mouthwashes, toothpastes. This is not a war at all. If it were, we would have lost long ago, overpowered by sheer numbers and evolutionary speed. This is something else, something like a lichen, something like a waltz. This waltz will last for all of human history. We must hold our partners carefully and dance well.

Here beneath the old wood crucifix, as I watch the faithful leave the little chapel in Chimayo, I marvel with them at the miracle beneath this adobe floor, the same miracle buried beneath most every place human feet have trod.

-Dr. Callahan is associate professor of immunology/public understanding of science in the Department of Microbiology, Immunology, and Pathology at Colorado State University in Fort Collins, Colorado. His research on immunity, infectious diseases, and self-perception has been published in poetry and two books of creative nonfiction in addition to scientific reports.

Gerald N. Callahan
email : Gerald [dot] Callahan [at] colostate [dot] edu

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