On the Japanese island of Okinawa, a cluster of villages produced so many people who lived past 100 that researchers spent decades studying their diet and eventually traced part of the effect to a purple sweet potato that supplied roughly 60 percent of daily calories through the first half of the twentieth century

On the Japanese island of Okinawa, a cluster of villages produced so many people who lived past 100 that researchers spent decades studying their diet and eventually traced part of the effect to a purple sweet potato that supplied roughly 60 percent of daily calories through the first half of the twentieth century

In 1949, American occupation authorities ran a food-intake survey across Okinawa and recorded something that would occupy nutritionists for the next fifty years: the islanders were getting roughly 69 percent of their calories from a single root crop, on a total intake of about 1,785 calories a day. The crop was the sweet potato, known locally as imo. Animal foods of every kind — pork, fish, eggs, dairy — supplied less than four percent. And for …