Why intermittent fasting has been a staple of long-living Blue Zones cultures for decades

Blue Zones founder and The Blue Zones Kitchen Cookbook author Dan Buettner has spent his career studying the longest-living people on the planet. Teaching people longevity-boosting habits is his bread and butter, so to speak. His travels and research have shown him a lot about how often people who live long, healthy lives eat and live.

While there are definitely dietary patterns that are solidly connected with longevity (ahem, the Mediterranean diet), Buettner has also found something else that many centenarians have in common: a natural tendency towards intermittent fasting, aka limiting eating to certain time periods within a given day or week.

“Some centenarians in Blue Zones regions [eat] large breakfasts and smaller dinners,” he said in a recent Ask Me Anything in Well+Good’s Cook With Us Facebook group. “Breakfast was traditionally a time when people would eat after fasting for a long period of time, breaking their fast, and there is research that going back to that tradition has positive benefits, even if you eat your dinner at 6 p.m. and eat your breakfast at 7 a.m,” he wrote. This might not sound like IF, but it’s very similar—the 16:8 plan, for example, has people eat for an eight-hour window during the day and fast for the remaining 16 hours.

Beyond being an OG practice in Blue Zones areas, there is research connecting intermittent fasting with living longer. “There is an association between intermittent fasting and longevity, but it’s important to note that this is a correlation, not necessarily a cause-and-effect,” says integrative medicine doctor Jill Baron, MD.

One factor: Intermittent fasting may help reduce the risk of certain chronic and age-related diseases, thereby potentially helping with longevity. A 2017 study found that people who fasted for five days a month for three months (eating 800-1100 calories per day) had lower blood pressure, blood glucose levels, and cholesterol levels—all biomarkers associated with cardiovascular disease—than people who ate normally for three months. A very small 2018 study on people with Type 2 diabetes found that medically-overseen intermittent fasting (where they fasted for 24 hours, three days a week) reduced participants’ insulin resistance, which ultimately allowed them to control their blood sugars without medication.

Curious about intermittent fasting? Here’s the 411 from a top dietitian: 

Additionally, there is some evidence that the act of fasting itself (in specific settings) seems to promote longer life. A 2019 review found that eating for six hours and fasting for 18 hours daily “can trigger a metabolic switch from glucose-based to ketone based energy” that allows for increased longevity along with a reduced risk of diseases like cancer. (This is similar to the mechanism behind the ketogenic diet, which forces your body into burning ketones (fats) for energy instead of carbohydrates.) A mouse study from 2019 also found that mice who fasted (whether it was through eating fewer calories or eating a large amount of calories once per day) just lived longer than mice who ate normally.

However, it’s important to note that research in this area is still super preliminary—many of the above-mentioned studies are either on mice or on super small populations of people, meaning that we don’t definitively know if intermittent fasting helps people live longer. There are also concerns from other experts in the health space about intermittent fasting’s safety for people who are pregnant, trying to get pregnant, or who have a history of disordered eating.

Buettner also acknowledges that implementing intermittent fasting might be harder for the average American than for octogenarians living in Sicily or Okinawa. For example, you may not get home from work until 7 p.m., so therefore you wouldn’t eat dinner until 8 p.m.—and thus not be able to eat breakfast the next day until noon. But he says that in cases like these, 10 hours of fasting is still doable; just eat your breakfast at 9 a.m. the next day instead of earlier. “Personally, I find good results for energy and my overall health in shortening my eating time, meaning I’ll go for some periods where I eat all my meals within an eight or 10 hour window,” he says.

Of course what you eat matters, too; if you fast for 10 or 16 hours a day but eat a diet high in sugar and ultra-processed food, you likely aren’t getting a ton of longevity benefits. “Something also to know about intermittent fasting is that it may cause someone to overeat later,” Dr. Baron adds. “That will end up increasing the risk for obesity, diabetes, and other factors that are not associated with longevity.” (The best way to eat for longevity, according to Blue Zones research, is to eat a variety of plants at each meal and minimizing sugar and high-glycemic foods.)

While there does seem to be a connection between intermittent fasting and longevity, both experts emphasize that what you eat is really what matters most. And if you’re hungry, it’s certainly okay—healthy, in fact–to eat. Besides, part of the joy of living a long, healthy life is enjoying meals with loved ones. And that’s true regardless of what time you’re eating.

These nine habits are linked to living a long, healthy life. And this Blue Zones quiz will predict how long you’re likely to live, based on your current lifestyle habits.