When researchers descended on this affluent city east of Los Angeles several years ago to determine why, the theories piled up: Perhaps it was the vegetarian diet kept by many Adventists? Maybe it was their close communal ties? Or the frequent use of sprawling trails in the parks here? 

But one thing seemed certain to researchers: residents were not living into the next century by eating fast food. 

So last week, when the City Council approved Loma Linda’s first McDonald’s restaurant, many residents bemoaned the decision, worrying that the officials were jeopardizing the city’s reputation as a paragon of healthy lifestyles. 

Wayne Dysinger, a physician and public health professor in the preventive medicine department at Loma Linda University’s School of Medicine, grew up in the city and remembers a time when there were no such restaurants. A generation ago, it was nearly impossible to even find meat within city limits. Now, he worries about his children. 

“We know from research that if a school is near a fast-food restaurant, the kids there are more likely to be obese,” he said. “We will never eliminate unhealthy choices, and pretty much everyone has an unhealthy treat once in a while. I am going to drive by that intersection every day and it’s fairly likely that they will say ‘Oh Daddy, can we stop there’ more often. Why do we need to encourage that?” 

The new McDonald’s restaurant would hardly be the first fast-food joint around — there are already a handful of places offering assembly-line burgers and fries within the eight square miles of the city. 

And the area has deep roots to the icon that so many residents detest: the site of the original McDonald’s restaurant is less than five miles away, in San Bernardino. 

Still, in one sign of Loma Linda’s historical distaste for fast food, restaurants are required to go through a special approval process for drive-through windows. Once, when business proved slightly sluggish, a local chain crafted a special vegetarian menu dubbed “Loma Linda specials.” 

A generation ago, nearly 80 percent of the city was Seventh-day Adventist; by most estimates, Adventists now make up about half of the city’s population of 23,000. But the influence of the religion on the town remains clear. Many businesses shut down early on Friday, in observance of Saturday as the Sabbath. One of the largest supermarkets in town is owned by the church-run university, and there are no meat products to be found. (Canned soy alternatives are available in abundance, including some under a Loma Linda brand.) Only large businesses and restaurants are authorized to sell alcohol, and there is a total ban on smoking. 

“You have to realize how easy it is to be healthy there, you don’t even have to think about it and it’s the default choice,” said Dan Buettner, an author and healthy living advocate who identified Loma Linda as one of four places in the world with a high concentration of people living healthy lives past the age of 100. “Your social network is all concerned about the same thing. They are really trying to preserve the culture that has been established for a really long time.” 

Adventist or not, it is difficult to speak to anyone here without hearing about Mr. Buettner’s special designation of the town, identified in his book “The Blue Zones: Lessons for Living Longer From the People Who’ve Lived the Longest,” published by National Geographic in 2008. 

It is not just Mr. Buettner’s book that feeds the sense of civic pride in health here. Nearly every resident has a connection with the sprawling Loma Linda University Medical Center, which serves as both the physical and cultural center of town. 

About 10 years ago, when the city denied plans for another fast-food restaurant, the developer responded with a lawsuit and the city eventually capitulated, said Mayor Rhodes Rigsby, who is also the assistant dean of the Loma Linda University School of Medicine. 

“I don’t think we should be getting into the business of legislating vegetarianism,” Dr. Rigsby said, adding that he would support having a citywide vote on whether fast-food outlets should be banned entirely from the city. “If this is something that people are really opposed to, that’s how we should deal with it.” 

What would happen during such a vote is anyone’s guess. Ellsworth Wareham, who stopped working as a heart surgeon only two years ago, at 95, is often used as an example of someone with more energy than someone half his age. Dr. Wareham attributes his health at least partly to the fact that he has been a vegan for the last 30 or 40 years (he does not remember precisely). 

Eating at home, he said, is the best way to ensure that one is eating healthy food. He is certainly not about to let the impending arrival of McDonald’s raise his blood pressure. 

“I don’t subscribe to the menu that these dear people put out, but let’s face it, the average eating place serves food that is, let us say, a little bit of a higher quality, but the end result is the same — it’s unhealthy,” he said. 

“They can put it right next to the church as far as I am concerned,” Dr. Wareham added. “If they choose to eat that way, I’m not going to stop them. That’s the great American system.”