The search for the “elixir of youth” has spanned centuries and continents – but recently, the hunt has centred on the Okinawa Islands, which stretch across the East China Sea. Not only do the older inhabitants enjoy the longest life expectancy of anyone on Earth, but the vast majority of those years are lived in remarkably good health too.
Of particular note is the number of people who reach 100 years of life. For every 100,000 inhabitants, Okinawa has 68 centenarians – more than three times the numbers found in US populations of the same size. Even by the standards of Japan, Okinawans are remarkable, with a 40% greater chance of living to 100 than other Japanese people.
Little wonder scientists have spent decades trying to uncover the secrets of the Okinawans’ longevity – in both their genes and their lifestyle. And one of the most exciting factors to have recently caught the scientists’ attention is the peculiarly high ratio of carbohydrates to protein in the Okinawan diet – with a particular abundance of sweet potato as the source of most of their calories.
“It is quite the opposite of current popular diets that advocate a high protein, low carb diet,” says Samantha Solon-Biet, who researches nutrition and ageing at the University of Sydney. Despite the popularity of the Atkins and Paleo diets, however, there is minimal evidence that high-protein diets really do bring about long-term benefits.
So could the “Okinawan Ratio” – 10:1 carbohydrate to protein – instead be the secret to a long and healthy life? Although it would still be far too early to suggest any lifestyle changes based on these observations, the very latest evidence – from human longitudinal studies and animal trials – suggest the hypothesis is worth serious attention. According to these findings, a low protein, high carbohydrate diet sets off various physiological responses that protect us from various age-related illnesses – including cancer, cardiovascular disease and Alzheimer’s disease. And the Okinawan Ratio may achieve the optimal dietary balance to achieve those effects.
Much of this research comes from the Okinawa Centenarian Study (OCS), which has been investigating the health of the ageing population since 1975. The OCS examines inhabitants from across the Okinawa prefecture, which includes more than 150 islands. By 2016, the OCS had examined 1,000 centenarians from the region.
Rather than suffering a prolonged demise, the Okinawan centenarians appeared to have delayed many of the usual effects of ageing, with almost two thirds living independently until the age of 97. This remarkable “healthspan” was evident across many age-related diseases. The typical Okinawan centenarian appeared to be free of the typical signs of cardiovascular disease, without the build-up of the hard “calcified” plaques around the arteries that can lead to heart failure. Okinawa’s oldest residents also have far lower rates of cancer, diabetes and dementia than other ageing populations.
Genetic jackpot
Given these results, there is little doubt that Okinawa has an exceptional population. But what can explain that extraordinary longevity?
Genetic good fortune could be one important factor. Thanks to the geography of the islands, Okinawa’s populations have spent large chunks of their history in relative isolation, which may has given them a unique genetic profile. Preliminary studies suggest this may include a reduced prevalence of a gene variant – APOE4 – that appears to increase the risk of heart disease and Alzheimer’s. They may also be more likely to carry a protective variant of the FOXO3 gene involved in regulating metabolism and cell growth. This results in a shorter stature but also appears toreduce the risk of various age-related diseases, including cancer.
Even so, it seems unlikely that good genes would fully explain the Okinawans’ longevity, and lifestyle factors will also be important. The OCS has found that Okinawans are less likely to smoke than most populations, and since they worked predominantly in agriculture and fishing, they were also physically active. Their tight-knit communities also help the residents to maintain an active social life into old age. Social connection has also been shown to improve health and longevity byreducing the body’s stress responses to challenging events. (Loneliness, in contrast, has been shown to be as harmful as smoking 15 cigarettes a day.)