Authors: Unknown
Mountain gorillas in Rwanda are not the regular dirt-eaters that elephants
are, but they do visit sites five or six times a year where all the members of a
group occupy themselves in digging and eating soil for about thirty minutes
at a time. This soil, located high up in the side of a volcano, is rich in both salt
and iron, and observers suspect that the gorillas may be after those two important nutrients. Mountain vegetation, after all, is usually very low in sodium, and gorillas, like all mammals living at high altitudes, need extra iron
for the extra red-blood-cell production that is required at those altitudes. The
easiest way for gorillas to get this extra iron may be these volcanic soils.
And here's another insight into human geophagy that animals help us to
see. Just as strict carnivores do not eat dirt or clay, human populations that include a lot of animal products in their diet also do not eat dirt or clay. Clayeating is rare, even nonexistent, among the Masai of Kenya, cattle-herders
whose diet consists largely of milk and blood. But it is extremely common
among the neighboring Kikuya, agriculturalists whose diet is based largely
upon plants.
Animal products are important both for what they have and what they
don't have. They have most of the minerals that humans and other animals
need to survive, including sodium, iron, phosphorus, zinc, selenium, and calcium (but only if the bones are chewed, since meat itself is low in calcium).
And they don't have the many toxins that plant foods have: the tannins in
acorns, the glycoalkaloids in potatoes, the phytates in soybeans. Because so
many of the plants we eat in the United States have been bred to lessen their
toxic load, we have the luxury of knowing very little about these chemicals,
which were designed to protect plants from being attacked by funguses as well
as animals. But they can cause severe and sometimes fatal damage. Some limit
the nutrients available for growth, while others act as poisons, releasing cyanides, carcinogens, and other dangerous substances, bursting red blood cells
and damaging neurons, kidneys, and the endocrine system.
Plant-eaters are not entirely at the mercy of the plants, though, and many
find ways around these toxins. Some plant-eaters process plants to remove the
most toxic parts, and some have become specialists in handling certain toxins,
like the koala, which eats only eucalyptus. Others consume clay along with
toxic plants so that the clay particles can absorb most of the toxins. Clays are ideal antitoxins for several reasons. Their very fine particles give them a large
surface area and make it likely that those particles will come into contact with
the toxins in foods. And their crystalline structure is layered with positively
charged ions, primarily of silicon and aluminum. Since many organic toxins
are also positively charged particles, they essentially trade places with the ions
in the clays then pass harmlessly through the digestive system.
Animals seem to be aware of the benefits of adding clay to a plant-based
diet, and in some animals, detoxification of plant foods seems to be the primary reason for eating dirt. In the study of the daily, dirt-eating behavior of
tropical, plant-eating birds in New Guinea, Jared Diamond found that the soil
chosen by these birds (cockatoos, parrots, and pigeons) is particularly good at
binding the positively charged molecules of strychnine, quinine, and tannic
acid that lace their diet of seeds and unripe fruits. The soil is not rich in any
minerals that the birds might need, but it binds one-tenth of its own weight in
toxins and has 50 percent more binding capacity than the surrounding soils
that the birds do not eat.
Dirt-eating in animals also allows us to see how irrational we can be about
dirt-eating in humans and how differently we regard the behavior of our own
species. While few scientists question the underlying functionality of this behavior in animals, in humans, such arguments have usually been dismissed.
Dirt-eating is seen as a sensible, instinctive way that animals can compensate
for deficiencies in their diet and/or remove toxins from their foods. In humans, it is a perverse activity that few educated persons would ever admit to.
Which brings me to the third thing that we need to know in order to understand the human practice of geophagy. In fact, most of us are geophagists
in that we seek salt from the earth or the oceans to add to our diet. We usually
don't think of salt as dirt, but salt is a deposit found in rocks, and clay and dirt
are nothing more than weathered rocks. Animals that are carnivores don't
need to add salt to their diet because the muscles and guts of their prey have
sodium enough to meet their needs. But most herbivores and omnivoresand that includes humans-cannot rely on diet alone for adequate amounts
of this nutrient, essential to nerve transmission, muscle contraction, and the
maintenance of fluid balance. Because salt is scarce in many parts of the
planet, and hence in the plants that grow in those places, many animals must
seek out salt licks or salt mines. The problem is particularly acute for inland
vegetarians, such as the mountain gorillas of Rwanda, or much of the population of India. Because of this inverse correlation between meat consumption
and salt requirements, a poor man, in general, needs more salt than a rich one.
And a poor country needs more salt per head than a rich one, a fact of nature that led Gandhi to protest the British policy of salt taxation and take his followers on a "salt march" to the sea.
We so take for granted this almost universal form of geophagy-the saltshaker-that we don't even see it as geophagy. And, therefore, we don't understand that geophagy is neither an uncommon nor an abnormal behavior,
but a reflection of the fact that being an omnivore is a tricky business in many
parts of the world. Humans need forty or fifty different nutrients to stay
healthy, and sometimes we have to go outside the bounds of what is considered food to find them. Or we have to add things such as clay to our diet in
order to turn toxic foods into nutritious ones. Since women, especially pregnant women, have a harder time meeting their nutritional needs, and since
pregnant women must also protect the child that is growing inside them from
the toxins in food, women tend to eat more dirt.
Calcium and iron present two of the biggest nutritional problems that
women face over the course of their lives. A woman's need for calcium increases dramatically during pregnancy, from 8oo to 1,200 milligrams per day,
a challenge everywhere on earth, but especially in places where calcium levels
in the soil are naturally low and/or in cultures where milk and milk products
are not a part of the diet. A woman's ability to absorb calcium from the foods
she eats increases during pregnancy, but to get the same amount of calcium as
in one glass of milk, she would have to eat two and one-half cups of beans or
two cups of cooked collards. Tofu is almost as good a source of calcium as
dairy products, so Asian women have no harder time meeting their calcium
needs than women in cultures where dairy is consumed, but women all over
the world can easily consume too little calcium during pregnancy and lactation, shortfalls that they will pay for later with bone fractures and other signs
of osteoporosis.
Some of the clays eaten by pregnant women in Africa provide large
amounts of calcium, up to 8o percent of a pregnant woman's RDA, assuming
a consumption pattern of too grams per day (the equivalent of a stick of butter). Others, however, provide only trace amounts of calcium. But, as Andrea
Wiley and Solomon Katz point out in a theoretical paper on the role that calcium might play in geophagy, clay consumption can help a woman's calcium
balance in ways other than by actually providing her with calcium. Clays can
slow down the motility of the gastrointestinal system and thereby increase the
time during which calcium can be absorbed from foodstuffs. And by binding
with secondary compounds in plant foods, clays can also release minerals, including calcium, with which these compounds often form complexes. The
traditional method of preparing corn tortillas in much of Mexico and Central America by boiling the corn with limestone markedly improves the calcium,
as well as the protein, content of the tortillas and is probably the reason for the
low incidence of osteoporosis in those same areas.
Iron presents an even longer-term problem for women, from the onset of
puberty until menopause, from around age fifteen to fifty-one. Women have
higher iron requirements than men, but they consume fewer calories. So even
Western diets-diets that include many more iron-rich types of meat than
those in less-developed countries-can leave women with shortages of iron.
Iron deficiency, not surprisingly, is the most common nutrient of deficiency in
the world.
In the United States, women make up for shortages of iron with supplements and fortified foods (and by consuming more food than they need-a
subject for another article). Elsewhere, they might visit clay pits or termite
mounds. The clays of termite mounds are rich in both calcium and iron and
supply a woman who eats at least twenty grams a day with more than ioo percent of her RDA for iron. It has never been proved that women eat these clays
in order to obtain extra calcium and iron, but it is telling that, in certain parts
of Africa at least, most of the pregnant population makes it a habit of visiting
termite mounds. And telling, too, that women must compete for these same
clays with many other animals, including giraffes, chimpanzees, and cattle.
The cattle, in their rush for these mineral-rich clays, have been known to
knock women and children down.
Another problem that becomes more difficult for women during pregnancy-and one that also inclines them toward dirt-eating-is the problem
of plant toxins. Many substances that are mildly toxic to adults are extremely
toxic to developing embryos. Some researchers have speculated that the nausea and food aversions that plague women during the first trimester help
women to avoid the ingestion of these harmful substances, but for women
who have no choice but to eat foods that are loaded with toxins, a daily dose
of clay could help to minimize their effects. Small amounts of clay might also
directly relieve the symptoms of pregnancy by changing the acidity of the
stomach and/or by absorbing excessive amounts of saliva. Whatever the actual
reasons why pregnant women eat dirt, dirt-eating is an integral part of the behavior of pregnant women in many parts of the world. "That's how you know
when you are pregnant," as one African informant says.
With all the examples I've given of dirt-eating in humans and other animals, with all the possible benefits that dirt-eating can provide, especially to
pregnant women, I'm not arguing that all dirt-eating in our species serves a
clear nutritional purpose. Nor that all dirt-eating is benign. Humans can abuse clay just like anything else they put into their mouths, and eating too
much clay can cause intestinal blockages that may have to be surgically removed and can sometimes result in death. Clay-eating also causes tooth abrasion (some dentists are able to pick out the geophagists in their patient population by the amount of wear on their teeth), and it's suspected of causing, not
curing, nutrient deficiencies, especially iron-deficiency anemia, a suspicion
that has been around since ancient times.
The relationship between clay-eating and anemia is a complex one that has
never been clearly resolved. Physicians have long observed that many of their
patients who eat dirt are anemic, but is clay-eating a cause of anemia or a consequence? Part of the confusion, investigators are beginning to realize, stems
from the fact that different clays have very different effects on a person's nutritional status. Certain clays are rich in easily absorbable mineral, but others
actually rob the body of nutrients and minerals. When clays are ingested with
food, the cations in the clays trade places with the cations in the food. So there
can be a net gain or loss of mineral nutrition depending on the clay and the
food. A clay may pick up an iron particle and leave behind an aluminum particle, a net loss for the consumer. Or it may pick up a toxic particle and leave
behind an iron particle, a substantial gain. Human and animal populations
presumably learn what clays to eat through trial and error, and over many
generations, but if that knowledge is interrupted through voluntary or forced
dislocation, new clays that may be substituted by these populations can do
more harm than good.
The experience of slaves in the New World may be an example of this. When
slaves were forcibly removed from Africa, they brought their well-established
clay-eating traditions with them, and plantation owners were soon commenting on their "mania for eating dirt." Owners came to blame this practice for
much of the illness they saw in the black population and for a new and often
fatal syndrome they called "Cachexia Africana," or "mal d'estomac," a syndrome characterized by sluggishness, anemia, and mental insensibility as well
as dirt-eating.
"The only appreciable signs of mental activity exhibited during the course
of this disease," wrote F. W. Cragin, a physician who described the syndrome
of Cachexia Africana in 1835, "are the crafty and cunning plans which the patient most subtily [ sic] matures, and as stealthily executes, to procures his desired repast ... of charcoal, chalk, dried mortar, mud, clay, sand, shells, rotten
wood, shreds of cloth or paper, hair, or occasionally some other unnatural
substance." Slave owners attributed these unnatural appetites to willfulness on
the part of their slaves and viewed geophagy as a slow method of suicide. And they tried, largely unsuccessfully, to break their slaves of the habit (and to protect their economic investment) by chaining perpetrators or by forcing them
to wear cone-shaped mouth locks, tin masks that covered the entire face.
In recent years, several researchers have revisited this once-common syndrome, second only to yellow fever as a cause of death among slaves in parts of
the South. Some have suggested that a deficiency of B vitamins, along with
hookworm infestation and intestinal parasites, brought on the symptoms of
earth-eating, as well as those of weakness, anemia, edema, and heart failure;
others, that the clays eaten by the slaves acted to bind dietary potassium and
iron and cause all the symptoms of the disease. But dirt-eating is still very
common in the South, and physicians see very few patients with symptoms
similar to those described by pre-Civil War physicians. So though it is conceivable that the specific clays the slaves ate in the New World initiated a new
and often fatal medical syndrome, it is more likely that slaves ate more and
more clay when their circumstances and diet left them malnourished, overworked, and unable to fight infections.