New Technique to Study Ancient Teeth Reveals Edo-Era Diet in Japan

Researchers analyzed DNA in tartar from the remains of 13 people who lived between 1603 and 1867

Researchers in Japan have taken a close look at the tartar on centuries-old teeth to get insight into what people ate during the Edo period.

Genetic material in the calcified muck, also called dental calculus—collected from skeletal remains in the Unko-in site in Tokyo—showed traces of rice and vegetables, as well as hints at the plants used in medicine and hygiene products, according to a paper published in PLOS One. The team confirmed its findings with foods listed in the historical literature from the period, which lasted from 1603 to 1867.

The researchers employed a genetic technique called “metabarcoding” to analyze 13 tartar samples. They present their results as an example of how the technique, typically used by ecologists to figure out animal diets based on the DNA found in scat, could be applied in archaeology.

“The technique will make it possible to survey what each individual ate,” Rikai Sawafuji, an archaeologist at the University of the Ryukyus, tells Masahiro Yoneyama at the Asahi Shimbun. It could also provide insight into staples of the era’s diet, Sawafuji says, because “plants detected from the teeth of many people’s remains were likely widely consumed.”

In metabarcoding, researchers search a sample—whether scat or tartar—for short, identifiable snippets of genetic code. Then they compare what they find to a known DNA barcode database. The snippets don’t appear in bacteria, and the researchers checked for genetic signs of plants, animals and fungi on the teeth.

The team looked for the genetic signature of rice first—a staple food in Edo-era Japan and today—and ultimately found traces of rice DNA on eight of the 13 samples. The researchers also found DNA that’s likely from vegetables including carrot, pumpkin, Japanese chesnut, Welsh onion, daikon radish and shiso perilla.

The analysis of the tartar didn’t turn up any evidence of meat-eating, but the researchers note in their paper that animal DNA might have been blocked by the same tool used to exclude human DNA from the results. According to Atlas Obscura’s Kristi Allen, hunting and eating land animals was uncommon and even illegal in Japan for hundreds of years beginning in the 6th century, when Korea introduced Buddhism to the country, and with it the teaching that any animal might be the reincarnation of a person. Eating pork or beef could require months of repentance. Upper classes sometimes treated it “as a special food with medicinal properties,” Allen writes. Unko-in, however, was more likely the burial site of common people who died in the middle or near the end of the Edo period.

The researchers also found evidence of tobacco on the remains, giving more weight to the theory that smoking was common at the time, since there was no wild relative of the cultivated plant in Japan at the time. The team detected signs of ginko and other medicinal plants, as well as a member of the Dipterocarpaceae family. The latter only grows in tropical regions and wouldn’t have grown wild in Japan. “Therefore, this cannot be explained without the existence of trade,” the team writes.

The DNA from the Dipterocarpaceae plant might have come from impurities in a substance called borneol that people used as a flavoring, along with clove, for the fine sand they used to scrub their teeth.

“Tartar DNA no doubt reflects what the person ate, so use of the substance will spread further,” University of Tokyo paleogeneticist Hiroki Ota, who was not involved in the research, tells the Asahi Shimbun. “But calculus [tartar] could be formed differently in differing dietary cultures. So the research accuracy needs to be improved by conducting a variety of methods using coprolites [fossilized feces] and other objects to uncover all details.”