On Okinawa, home to one of the world's highest concentrations of centenarians, people follow an eating rule that predates modern nutrition science by hundreds of years.
It is called hara hachi bu, and it means stopping when you are about 80 percent full. Researchers who have tracked the population for decades link the practice to a diet roughly 20 percent below what most adults eat freely, and to low rates of heart disease, stroke, and certain cancers.
A first-of-its-kind clinical trial has since given the idea a mechanism.
In February 2023, Columbia University epidemiologists reported in Nature Aging that two years of modest calorie restriction measurably slowed the pace of biological aging in 220 healthy adults, a 2 to 3 percent reduction that the National Institute on Aging says translates to a 10 to 15 percent drop in mortality risk over time.
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Where the rule actually came from
Hara hachi bu is rooted in Confucian teaching and has been part of Okinawan food culture for centuries. In practice, it means finishing a meal while there is still a little room in the stomach, rather than eating to the point of feeling full.
The Okinawa Centenarian Study, an ongoing research project since 1975, has documented what that looks like in daily life.
In a 2007 paper in the Annals of the New York Academy of Sciences, researchers Bradley Willcox and D. Craig Willcox reported that traditional Okinawan elders consumed about 1,800 to 1,900 calories a day. That is roughly 20 percent below what people eat when they are allowed to eat freely, and the population had body mass indexes of 18 to 22, well below the American average.
Why the 20-minute lag matters
The reason hara hachi bu works has to do with how slowly the body signals fullness. The brain does not receive the message that the stomach is filling up in real time. There is a delay, and by the time it arrives, most people have already eaten past the point they intended.
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Susan Albers, PsyD, a psychologist at Cleveland Clinic, puts it this way. "Your stomach takes 20 minutes to digest your food. By that time, you've already left the table." Stopping at 80 percent gives the body the window it needs to catch up. Ten or fifteen minutes later, the reader typically feels comfortably full, not stuffed.
Albers frames the practice as a coaching tool rather than a diet. "This is good advice for overeaters who are learning how to fill their stomachs only just enough," she says. She suggests starting small, leaving one bite behind on the plate, and building from there.
What the aging trial actually showed
The Nature Aging trial, led by first author Raghav Waziry and senior author Daniel Belsky, PhD, associate professor of epidemiology at Columbia University's Mailman School of Public Health, drew on data from the CALERIE study. Participants without obesity were randomly assigned to either restrict calories by 25 percent or eat as usual for two years.
Using an epigenetic clock called DunedinPACE, which reads changes in DNA methylation to estimate how fast a person is biologically aging, the researchers found the calorie-restricted group aged more slowly. The effect was small in percentage terms, but the National Institute on Aging notes it is on par with the mortality benefit seen from quitting smoking.
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Hara hachi bu is not a 25 percent cut. It is closer to a 10 to 20 percent reduction, and it happens without counting. But the trial supports the underlying idea that eating somewhat less, over the long term, changes how the body ages.
How to actually apply it
Practitioners at Cleveland Clinic and Northwell Health describe hara hachi bu as a mindful-eating strategy with low risk for healthy adults. The practical moves are small.
Eat slowly. Use smaller plates so a normal-looking portion is already less food. Pause partway through the meal and check in on hunger before reaching for more.
Serve dishes family-style away from the table so seconds require a conscious decision. Aiming for roughly two-thirds to three-quarters of what would otherwise fill the plate is the target most clinicians describe.
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The practice is not right for everyone. As Aisling Pigott, a lecturer in dietetics at Cardiff Metropolitan University, notes in The Conversation, it is not meant to be restrictive and may not suit athletes, growing children, older adults at risk of undernutrition, or people with conditions that raise their nutritional needs.
Anyone with a history of disordered eating should talk to a doctor before adopting rules around portion size.
For most healthy adults, though, the appeal of hara hachi bu is that it asks for attention rather than sacrifice. It replaces a number on a plate with a question at the table. Am I still hungry, or am I just still eating?
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.