Terra sigillata in action: why primates eat dirt

Leave it to PharmGirl, MD, to point me in the direction of a story that addresses the core theme of this blog: not only can medicines come from the Earth, but the Earth can itself be medicine. This time we’re not talking about South Carolina “sandlappers” as detailed in my inaugural post here as authored originally at the old blog. (For newcomers, you’ll get this gist if you also read, “Why Terra Sigillata?”).
Instead, we wish to point your attention to a LiveScience article by Clara Moskowitz entitled, Why Chimps Eat Dirt. The practice of eating soil, known as geophagy, is common among primates. As I noted in explaining the history of terra sigillata the medicine, soils often contain minerals or fats like kaolin that soothe mild gastrointestinal disorders.
However, Moskowitz’s article on the work of Noémie Klein, François Fröhlich, and Sabrina Krief at the National Museum of Natural History in Paris points to an even more interesting consequence of geophagy: chimps that eat soil before eating a specific plant create a situation where the activity of anti-malarial components of the plant are enhanced:

By studying samples of soil eaten by chimpanzees in Kibale National Park in Uganda, a research team led by Sabrina Krief of the Muséum National d’Histoire Naturelle in Paris found that eating soil with their meals boosts the anti-malarial properties of plants the chimps eat.
Krief collected the dirt along with leaves from one of the chimps’ favorite foods, the Trichilia rubescens plant. She found that when eaten alone, the leaves had no pharmacological effect, but when combined with soil, the mixture had clear anti-malarial properties.
Scientists previously suspected that animals might eat dirt when stressed or as a source of missing minerals. This new result is the first suggestion that the combination of soil and other foods could have health benefits, Krief said.

I don’t have access to the primary article in Naturwissenschaften this Sunday evening, but I’m really excited to investigate the chemical identity of the anti-malarial compounds and the proposed mechanism of geophagic potentiation or synergy. Does the soil increase the bioavailability of the relevant compounds or does the soil contain microorganisms that biotransform the plant’s secondary metabolites to active anti-malarial compounds?
In the meantime, here is the abstract:

Geophagy, the deliberate ingestion of soil, is a widespread practice among animals, including humans. Although some cases are well documented, motivations and consequences of this practice on the health status of the consumer remain unclear. In this paper, we focused our study on chimpanzees (Pan troglodytes schweinfurthii) of the Kibale National Park, Uganda, after observing they sometimes ingest soil shortly before or after consuming some plant parts such as leaves of Trichilia rubescens, which have in vitro anti-malarial properties. Chemical and mineralogical analyses of soil eaten by chimpanzees and soil used by the local healer to treat diarrhoea revealed similar composition, the clay mineralogy being dominated by kaolinite. We modelled the interaction between samples of the two types of soil and the leaves of T. rubescens in gastric and intestinal compartments and assayed the anti-malarial properties of these solutions. Results obtained for both soil samples are similar and support the hypothesis that soil enhances the pharmacological properties of the bio-available gastric fraction. The adaptive function of geophagy is likely to be multi-factorial. Nevertheless, the medical literature and most of occidental people usually consider geophagy in humans as an aberrant behaviour, symptomatic of metabolic dysfunction. Our results provide a new evidence to view geophagy as a practice for maintaining health, explaining its persistence through evolution.

We can talk more when I get the original article but this is pretty cool stuff, eh?


4 thoughts on “Terra sigillata in action: why primates eat dirt

  1. Thanks is pretty neat; I’ll be looking forward to your analysis! I’ve heard of chimpanzees eating soil after consuming plants, but I hadn’t heard of it occurring before they consumed other foods. I’ll definitely have to check this one out, too!

  2. This is interesting indeed. It rather hits on a question that my partner and I were discussing, after I mentioned a question that a commenter at Orac’s put forth; “Where do people get the idea that these [plant “medicines”] ever had a chance of working in the first place?”
    I actually provided an answer to the rather direct aspect of the question, as it relates to modern CAM, i.e. that there are many a pharmacopia out there. That herbals were the mainstay of medicine for a very long time. But it did get me thinking about the more abstract of the same question, i.e. where did the idea come from in the first place, especially for the ones that really work?
    This really raises more questions than it answers, but I have to wonder about it, as it seems to me, the geophagy would be pretty instinctual. Lending to the question of where said instinct comes from, whether there is an evolutionary component to it.
    Beats my theory that we managed to discover medicinal plants, from the discovery of intoxicating plants.

  3. Excellent post and excellent paper, I’ve just read it and think I have some clue as to the action of the soil. Soil has been recently thought to be involved in the abiotic origin of life due to its capacity of catalyzing the formation of RNA oligomers. Clay minerals expose electrical charges which can adsorb organic ions and make these ions approach one another, so that they can react. If the anti-malarial compounds are present in the plants in an inactive form, the action of the adsorbing clays may be of a catalyst activating them.

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