Eating dirt helps chimps fight off malaria, researchers from the Muséum National d'Histoire Naturelle in Paris reported Wednesday.

Sabrina Krief and her colleagues had observed chimps eating soil (geophagy), a practice common among animals but usually discouraged by humans, where it has even been linked to mental-health issues, the researchers said in a release.

Chimps eat dirt to boost the anti-malarial properties of certain plants, French researchers say.
(CBC)

But they suggested that geophagy can be explained in chimps as a way to enhance the health effect of certain plants, and concluded that may explain why it has continued through evolution.

The researchers took 14 samples of soil eaten by chimpanzees in Kibale National Park in Uganda. The animals had been seen sampling the dirt before or after eating certain plants, such as the leaves of Trichilia rubescens, which has been shown to have some anti-malarial properties.

The researchers took plant samples, too, and created a laboratory model to replicate the chimps' chewing, gastric and intestinal processes.

The soil and leaves were analyzed, both separately and as a mixture.

"Before being mixed with the soil, the digested leaves showed no significant anti-malarial activity. However, when the leaves and soil were digested together, the mixture had clear anti-malarial properties," the release said.

They also noted that the soil they tested was very similar to the soil used by a local healer to treat diarrhea. Both contained the clay mineral kaolinite, used in diarrhea medicines.

The study is to be published online this week in the journal Naturwissenschaften.