The findings, published in the Proceedings of the National Academy of Sciences (PNAS) journal on Monday, indicate that Palaeolithic Europeans ground down plant roots similar to potatoes to make flour, which was later whisked into dough.

"It's like a flat bread, like a pancake with just water and flour," said Laura Longo, a researcher on the team from the Italian Institute of Prehistory and Early History.

"You make a kind of pita and cook it on the hot stone," she said, describing how the team replicated the cooking process. The end product was "crispy like a cracker but not very tasty," she added.

The grinding stones, each of which fit comfortably into an adult's palm, were discovered at archaeological sites in Italy, Russia and the Czech Republic.

The researchers said their findings throw mankind's first known use of flour back some 10,000 years, the previously oldest evidence having been found in Israel on 20,000 year-old grinding stones.

The findings may also upset fans of the Paleolithic diet, which follows earlier research that assumes early humans ate a meat-centered diet.

Also known as the caveman diet, the regime frowns on carbohydrate-laden foods like bread and cereal, and modern-day adherents eat only lean meat, vegetables and fruit.

It was first popularized by the gastroenterologist Walter L. Voegtlin, whose 1975 book lauded the benefits of the hunter-gatherer diet.

(Reporting by Brenda Goh, Editing by Steve Addison)