By DAN BUETTNER May 22, 2015 10:19 a.m. ET

The secrets of the world’s longest-lived people include community, family, exercise and plenty of beans.
In Sardinia, there are 21 centenarians in a population of 10,000. Only about four in 10,000 Americans reach the 100-year mark.

In a string of whitewashed villages in the mountains of the Italian island of Sardinia, there are 21 centenarians in a population of 10,000. Only about four in 10,000 Americans reach the 100-year mark. So what do the Sardinians know that our own diet-and-health obsessed country doesn’t?

In April, I visited this epicenter of longevity along with Michel Poulain, a Belgian demographer; Paulo Francalacci, an Italian evolutionary geneticist; and Gianni Pes, an Italian physician and medical researcher. For the past 11 years, we have been studying what we call “blue zones” around the world—places where people live the longest with the lowest rates of chronic disease.

When I first reported on this area a decade ago, scientists theorized that genes played a role in the extraordinary longevity of Sardinians. This enclave of 14 villages is home to one of the world’s most genetically homogenous populations, second only to that of Iceland.

Since then, the notion of a genetic advantage has been called into question. According to Dr. Pes, several studies have shown that the genetic markers of the centenarians—including markers associated with cardiovascular mortality, cancer and inflammation—don’t diverge significantly from those of the general population.

Based on the work we did in Sardinia and four other blue zones, a team of researchers at the University of Minnesota helped us to reverse-engineer a diet of the world’s healthiest populations. We gathered 155 dietary surveys from all five areas, covering the eating habits of the past century, and came up with a global average.

On my recent visit to Sardinia, I spent an afternoon in the village of Villagrande with a baking circle of sorts: five women, including a grandmother, daughter and granddaughter, who get together every few weeks to bake traditional sourdough bread, leavened with lactobacillus cultures and yeast.

I was first drawn to them because of the bread. Dr. Pes had published a study showing that Sardinian sourdough bread actually lowers a meal’s glycemic load. (Most bread metabolizes almost immediately into sugar, spiking insulin levels.)

After spending a couple of hours with these women, I realized that the bread was only one ingredient in a larger group of benefits that the bread-making occasioned. The women also had to chop wood and stoke the oven. They had to knead the dough for 45 minutes (more exercise than going to the gym).

Life in these villages is very social. People meet on the street daily and savor each other’s company. They count on one another. If someone gets sick, a neighbor is right there. If a shepherd loses his flock, other shepherds rally round with donated sheep to rebuild the flock.

In the nearby hamlet of Mores, I met 94-year old Salvatore Pinna and three of his friends, whose ages ranged from 88 to 90. They wore woolen newsboy caps and the kind of rugged tweed jacket fashionable in both sheep pastures and the village square. They get together every morning for coffee, again in the afternoon to play dominoes and at night to drink homemade Cannonau wine. Two of them were living alone, but as one told me, “We’re never alone.”

When it comes to longevity, the long-standing support of a community is significant. In the U.S., you’re likely to die eight years earlier if you’re lonely, compared with people who have strong social networks. In Sardinia, “One hand washes the other, and they both wash the face,” as Mr. Pinna told me, summing up the social symbiosis.

He and his friends serve as repositories of agricultural wisdom, which they routinely share by advising local vintners how to cope with temperamental weather and various insect pests. They are pillars of the local economy and are prized for it.

A fanatic zeal for family has also survived here. Neither work, hobbies, friends nor a sports team would ever divert serious attention away from a spouse or children. In turn, parents and grandparents move serenely into old age, secure in the knowledge that their children will care for them. There are no retirement homes here.

What we found in Sardinia is similar in other blue zones. None of the spry centenarians I’ve met over the years said to themselves at age 50, “I’m going get on that longevity diet and live another 50 years!” None of them bought a treadmill, joined a gym or answered a late-night ad for a supplement.

Instead, they lived in cultures that made the right decisions for them. They lived in places where fresh vegetables were cheap and accessible. Their kitchens were set up so that making healthy food was quick and easy. Almost every trip to the store, a friend’s house, work or school occasioned a walk. Their houses didn’t have mechanized conveniences to do house work, kitchen work or yard work; they did it by hand.

People in the blue zones were nudged into physical activity every 20 minutes, my team estimated. This activity not only burned 500 to 1,000 calories a day; it also kept their metabolisms humming at a higher rate.

Americans spend about $110 billion a year on diets, exercise programs and supplements, but self-discipline is a muscle that fatigues. Research shows that such short-term efforts fail for almost everyone in less than three years. By contrast, successful strategies to avoid disease and yield longevity require decades of adherence—or entire lifetimes

For enduring gains in health in the U.S., we should shift our tactics away from trying to change individual behavior to optimizing our surroundings. We should make healthy choices not only easy, but also sometimes unavoidable—so that longevity “just happens” to Americans.

— Mr. Buettner is a National Geographic fellow and the author of “The Blue Zones Solution: Eating and Living Like the World’s Healthiest People.”