Human hairs that were mixed into recycled paper during the Edo Period (1603-1867) are providing valuable information about the dietary habits of people around Japan during that time.

A team of researchers from Ryukoku University and other institutions said the hairs may have accidentally landed in pulp used in the recycling method when publishing was booming in major cities in Japan.

But according to another theory, paper makers deliberately mixed hairs in the fiber to strengthen their products.

Whatever the reason, the publishing dates of books with pages containing hair provide a highly accurate time frame for the foods eaten by Edo Period people.

To study diets, the research team analyzed the ratios of isotopes of carbon and nitrogen contained in 130 hairs found in books published at different times and places.

The results showed the ratio of sea fish consumption in Japanese diets gradually rose over 200 years from 1700.

The increase is attributed to improved fishing techniques that led to larger catches of herring and other species.

By area, people in Edo, today’s Tokyo, tended to consume more grains other than rice, such as “hie” and “awa” millet, compared with people in other regions.

Edo people were more likely to consume white rice than brown rice. The consumption of other grains that were rich in vitamin B1 indicates that they understood that these foods could prevent beriberi, one of the so-called Edo diseases, the researchers said.

“I would like to study in detail whether people’s diet changed after a famine or other major events,” said Atsushi Maruyama, professor of ecology at Ryukoku University and a member of the team.