By Paula Pebsworth, PhD

M. Martin and P. Pebsworth collecting soil samples – Photo P Pebsworth

M. Martin and P. Pebsworth collecting soil samplesPhoto P Pebsworth

Did you know that people and other animals eat soil? Like, lots of animals and lots of soil?! I’ve studied soil eating for more than 10 years and still find this curious behavior absolutely fascinating. Soil eating is formally known as “geophagy” for non-human animals and “pica” for humans. It’s not eating a little bit of soil left on your fresh radishes – it’s purposely and deliberately eating soil. And it’s not just any old dirt. It’s special dirt that humans admit walking miles to reach because they crave it. Soil eaters can’t tell you why they crave soil, only that they do.

I study soil eating in monkeys and apes and I can’t tell you what goes through their minds but I think eating soil is like taking a multivitamin. Some days you need vitamin C from the mix, other days it’s potassium, and other days it’s like taking a Tums ®. I had the pleasure of moving with a large troop of chacma baboons for several years. During some seasons, they went to their favorite dirt dinner – every. single. day. That’s right – I said daily. It became clear that some individuals stayed there a long time while others dined and dashed. At the dirt diner – there was a couple of favorite “chairs”. If someone of higher rank was eating soil there, you had to wait your turn. This told me that they liked some soil better than others. As a good biologist, I tried the soil in several different places. I felt a bit like Goldilocks. One was too salty, one was too sandy, and one was just right – if soil in your mouth can be right. The “just right” soil was the one they waited their turn for. If you don’t believe me – see it for yourself here.

The other thing that surprised me was how long some of the pregnant females spent eating soil. My friends who study soil eating in humans have told me that there’s a strong association between soil eating and pregnancy. Hmmm….why might that be and what the heck can you get from eating dirt?!!

When I tell people about my research, they immediately tell me that animals must be eating soil for minerals. Well, maybe. The soil eaten by the troop of baboons that I studied was pink, ochre, and white. The preferred soil was white. Pink and ochre soil color usually indicates that it contains iron. If baboons ate the soil for iron then it would have to be available for the body. To test this idea, I used a fancy analysis to test whether the iron from the soil was bioavailable. Meaning that the stomach, small, and large intestine could break up the soil and the micronutrients found in the particles of clay could be released and absorbed by the body. It turned out that the iron wasn’t bioavailable and there was no difference in bioavailable iron between the pink and white soil. The iron was tightly bound inside small clay particles and the digestive process couldn’t break it up and free the iron. Obviously, some minerals are water soluble (like salt) so they are available but not all.

In addition to micronutrients, soil may be eaten because the fine clay particles commonly found in eaten soil can line the gastrointestinal (GI) tract – kind of like a mud mask. Soil can protect your GI tract from plant toxins, bacteria, and viruses. How do I know that you ask? Well, again I ran some tests in the lab and I measured plant toxins found in food eaten by the baboons. Then I measured the plant toxins again after I mixed it with the preferred soil and digested it under the same conditions of baboon stomachs. I found that the soil bound up tannins and alkaloids. This is great news as too many tannins can give you a stomach ache. Again, I suspect that soil eating serves a couple of purposes – micronutrients and protection. I’m not suggesting that we all start eating soil to cure what ails us, but I suspect that there will come a day when people will return to a simpler life without so many pharmaceutical drugs.
When that day comes, you might want to put some healing soil in your medicinal cabinet or grab a seat at your local dirt diner.

Adult female baboon eating soil  Photo P Pebsworth

Adult female baboon eating soil  Photo P Pebsworth

Best seats at the Dirt Diner - Photo P Pebsworth

Adult female baboon eating soil  Photo P Pebsworth

Juvenile at Geophagy Site - Photo P Pebsworth

Adult female baboon eating soil  Photo P Pebsworth

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