Centenarians on the Japanese island of Okinawa historically obtained nearly 69 percent of their daily calories from sweet potatoes, according to publication Space Daily.
An investigation conducted by the American occupational administration in 1949 revealed that animal products made up less than four percent of the islanders' total caloric intake at the time, with pork, fish, eggs, and dairy combined contributing a minimal portion of their diet.
The traditional Okinawan diet was far more varied than popular descriptions suggest, featuring leafy greens, soy, seaweed, and bitter melon alongside sweet potatoes. Pork was consumed only occasionally, fish was not a primary staple, and rice was regarded mainly as a festive food. Overall, carbohydrates accounted for approximately 85 percent of the diet, while proteins made up nine percent and fats comprised six percent.
Laboratory studies of sweet potatoes have demonstrated antioxidant and anti-inflammatory properties, though researchers note there is insufficient evidence proving these qualities directly extend human life. Space Daily reported that the history of the island's diet is stranger and less reliable than popular accounts suggest.
Post-war dietary shifts and demographic changes
The Okinawan dietary pattern later became a central example in the concept of Blue Zones, a term coined during research into long-lived populations in Sardinia, Italy. Journalist Dan Buettner popularized the concept, which identifies Okinawa alongside Sardinia, the Nicoya Peninsula in Costa Rica, the island of Ikaria in Greece, and a Seventh-day Adventist community in Loma Linda, California, as regions with unusual concentrations of centenarians.
Demographic data gathered over subsequent decades provided researchers with significant comparative evidence regarding the islanders. Okinawans who are currently classified as centenarians grew up eating the traditional sweet potato diet, whereas their children and grandchildren adopted different eating habits following the end of the Second World War in 1945.
After 1945, canned meat, wheat flour, sugar, and fried foods spread across Okinawa. Between 1950 and 1960 alone, sweet potato consumption plummeted by approximately 90 percent as islanders replaced the crop with rice, bread, and pork.
Following these dietary changes, demographic markers shifted dramatically. By 2000, male life expectancy in Okinawa fell to 26th place among Japan's 47 prefectures, down from its top ranking maintained for nearly 30 years, while obesity rates climbed rapidly. Space Daily noted that this decline formed a primary argument supporting a link between traditional diets and health.
Lifestyle factors and longevity research
Longevity experts emphasize that diet cannot be separated from broader Okinawan cultural practices, including the tradition of hara hachi bu, which instructs diners to leave the table slightly hungry. Low caloric intake combined with high levels of daily physical activity created a lifestyle pattern that researchers believe may be more significant than any individual food item.
Space Daily noted that the sweet potato was not the entire answer, nor even necessarily the largest part of it, but served as the caloric foundation upon which the rest of the diet rested.
A comprehensive review in 2026 covering more than half a century of centenarian research concluded that no single food, gene, or lifestyle habit explains why certain individuals reach extreme old age. Instead, researchers attribute exceptional longevity to a combination of plant-based nutrition, regular physical movement, social connections, personality traits, genetics, and chance.
Scientific skepticism surrounding Blue Zones
However, the concept of Blue Zones has faced growing scientific skepticism, according to news agency UNIAN. Researcher Saul Justin Newman conducted an investigation into global longevity claims and challenged the existence of regions with abnormally high concentrations of 100-year-olds.
Newman discovered that almost no individuals recorded as living beyond age 110 possess verified birth certificates, while famous historical centenarians frequently lack official death certificates. His research indicated that designated Blue Zones consistently align with impoverished, poorly developed areas characterized by inadequate nutrition and limited access to healthcare, where extreme age claims often stem from missing records, reporting errors, and pension fraud.
