Chimpanzees are like us in many ways. They can cook, they enjoy a good drink here and there, they share about 95 percent of our DNA. Now research finds another similarity: Chimps are taking mineral supplements and doing "detox" diets — by eating clay.
Researchers observed chimps in the Budongo Forest of Uganda eating clay from clay pits and drinking water sprinkled with clay from holes under trees, according to a study published in PLOS ONE on Tuesday.
Researchers first noticed this behavior a few years ago, and it started getting quite popular among the chimps. The animals create "leaf sponges" to drink the water. They chewed up leaves, dipped them into the water holes, then chewed them again to squeeze out the water with their tongues. The chimps also used their fingers to extract lumps of clay directly from the ground to eat.
"A chimpanzee's diet is mostly leaves, fruits and the occasional monkey. They sometimes eat other things — bark, rotting wood and even soil," says Cat Hobaiter, a researcher at University of St. Andrews in the U.K. and co-author of the study.
Those foods, she explains, are a good source of minerals. So is clay, which is why the Budongo chimps have always eaten some, she says. (Humans also eat clay — more on that below.)
It's more common for chimps to get their mineral supplements from sources like decaying swamp trees, Hobaiter says. Deforestation, however, has meant there's less of this rotting wood for chimps to chew on. So it looks like the chimps "have to compensate for the loss of the mineral-rich wood by increasing the amount of clay they eat," Hobaiter says.
There's another reason why chimps chomp clay, she says: It's good for the "detoxification" of the tannins in their diet.
You see, the leaves these chimps eat contain lots of tannins — polyphenols that have bitter, astringent properties. We eat tannins, too — in foods like chocolate, tea and wine — but not nearly as much as chimps do. Tannins, when present in high amounts, have been known to turn some animals off their food.
That's where clay comes in. The Budongo chimps eat a type of clay called kaolin. The mineral-binding structure of this clay, the authors write, aids in digestion and "counteract[s] over-acidity and toxins." In other words, the clay seems to neutralize the tannins in the animals' diet, Hobaiter explains.
These chimps aren't the only ones who munch on clay. As The Salt reported last year, there's evidence that the practice is ancient among humans, too, and people in many parts of the world still do it. Eating clay is considered part of the disorder pica, in which people compulsively crave things that aren't food. But some researchers theorize that the habit of eating clay evolved as a protective measure, and that the clay might work as a "mud mask for the gut" in humans, helping to absorb poisons. (However, as one scientist told The Salt last year, that practice could also absorb useful nutrients.)
As for the chimps in the study, rest assured, they "did not have any evidence of digestive problems," says Vernon Reynolds, a professor emeritus of biological anthropology at Oxford University and the lead author of the study. "They're all perfectly healthy, and so it was preventative rather than curing."
"It's actually a common practice in many primates," Hobaiter says. "And that includes us."
As for modern-day human "detox diets"? As we've reported, medical experts say they're baloney.
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