Ancient humans may have eaten a pesky weed to fight off cavities

July 16

A skeleton of a young male whose plaque was analyzed: This is one of the three Late Meroitic graves identified at the cemetery. (Donatella Usai/Centro Studi Sudanesi and Sub-Sahariani)

For thousands of years, a new study indicates, prehistoric humans in central Sudan ate purple nutsedge. Today, we consider the plant a weed — one of the peskiest. But for those ancient humans, the plant was both a staple carbohydrate and a dental health aid: Whether or not they knew it, purple nutsedge was probably protecting their teeth from cavities.

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Luckily, our ancestors hadn’t caught on to flossing yet, because this nutritional revelation, published Wednesday in the open-source journal PLOS ONE, comes from the chemical analysis of ancient plaque. Researchers extracted the calcified dental plaque from skeletons found in a multi-period cemetery — one used for at least 7,000 years.

The time span is important, researchers said. Because the remains span pre-agricultural periods (when humans relied on hunting and gathering) to the beginnings of agriculture, we know that, for some reason, humans continued to eat purple nutsedge when they were capable of cultivating crops.

Our ancestors may have recognized purple nutsedge — today commonly known as nut grass — for its medicinal properties, said Karen Hardy, study author and Universidad Autònoma de Barcelona archaeology professor. Recent studies, she said, have indicated that the plant can fight the growth of Streptococcus mutans, a bacterium that causes tooth decay.

Sure enough, the skeletons examined in central Sudan had an unexpectedly low number of cavities. “We don’t know much about [purple nutsedge and cavities],” she said. “This is very recent work. But we expect that biologists will develop that, so we can have a better idea of whether this theory is correct.”

Whatever the reasoning behind its longstanding popularity, Hardy said, the presence of a nuisance weed as a dietary staple is intriguing. “Without question, the purple nutsedge was the really surprising and exciting finding,” she said. “Today, we use this as animal fodder. Its use as a food source has been completely forgotten.”

Even if we don’t go back to chewing on purple nutsedge, the finding represents an ongoing shift in anthropologists’ understanding of pre-agricultural people.

Far from the meat-centric eaters that inspire our modern “Paleolithic” diet plans, our ancestors may have valued and understood plants long before they knew how to cultivate them.

Hardy said the same chemical analysis used on the plaque in this study — a complex method often used in the petroleum industry, but not used widely by chemists in other fields — could reveal more of the plants that our pre-agricultural ancestors craved.

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