NEW YORK -- The city that never sleeps is still snoozing peacefully when John Kubacki trots out his front door for a sunrise run in Central Park.

Across town, Patricia Brawer is already pumping iron with her personal trainer.

Soon Toni Landau will be striding briskly on the treadmill in her bedroom, just like she has six days a week for the past 12 years.

There's a name for these people. Dr. James Hill, an obesity expert at the University of Colorado Health Sciences Center in Denver, calls them "successful losers."

They are people who lost a lot of weight a long time ago and have managed to avoid regaining it. They are remarkably rare in our increasingly oversized nation. And, Hill says, they have a great deal to teach the rest of us about achieving and maintaining a healthy weight.

Obesity has become so common in the United States that it threatens to overtake smoking as public health enemy No. 1. One in four American adults is clinically obese, an increase of 50 percent over 20 years ago. Almost half of adults are overweight. Between 1980 and 1994, the percentage of obese teen-agers doubled.

Physicians estimate that 300,000 Americans die annually due to obesity-related illnesses, which include heart disease, gall-bladder disease, diabetes, stroke, some cancers and arthritis.

Defusing a time bomb

"Obesity is a time bomb," warns George Bray, an obesity expert and professor of medicine at Louisiana State University.

Seven years ago, Hill and a few colleagues began to study people who had defused their own obesity time bombs. They created the National Weight Control Registry, and recruited 3,000 people who had lost at least 30 pounds and kept it off for a year or more to sign up for it by calling a toll-free number (800-606-NWCR).

Each year, the people on the registry fill out questionnaires about their diet, exercise and other weight-related factors and the scientists enter the information into the registry.

The idea is to figure out what successful losers do to maintain their weight. Hill isn't too interested in how they lost it in the first place because, as any serial dieter knows, losing weight is easy compared to keeping it off in the long run.

Successful losers tend to have four things in common, Hill says. Most, but not all, weigh themselves frequently and eat breakfast every day. Even more important, they consume a low-fat diet and exercise regularly.

"These behaviors aren't real surprising, Hill says. "They do all of the things we're telling them to do."

So it's no big secret what successful losers do to keep their weight down. The real secret is HOW they keep at it, shunning dessert and sweating through a daily workout, year after year after year.

To learn that, you have to talk to the losers themselves.

"You should see me do push-ups," says Brawer, a lifelong New Yorker who works on Wall Street. "I'm strong, like bull."

Brawer had been on and off diets her entire life when she walked into a gym for the first time nine years ago. "I'm really going to hate it," she thought.

She was 47 years old, weighed almost 180 pounds and considered physical exercise a hateful chore.

Within a few weeks her opinion of exercise had changed for good -- and so had her body.

"It was the most amazing immediate gratification," Brawer says. "I felt strong and I felt empowered."

Now she lifts weights three times a week. Her weight hovers around 135 pounds, and the same woman who once fantasized about squeezing into a size 12 wears a 10.

"It's so exciting," Brawer says. "I'm like this whole new person."

Personal transformation

Almost every successful loser agrees that it took a complete personal transformation to keep the weight off, not just a minor adjustment -- and that exercise had to be part of it.

Six years ago Shavon Stirling was overweight and unemployed. Her marriage disintegrating, she resolved to turn her life around with exercise. Stirling started by walking a six-mile loop around New York's Central Park every day. As she lost weight and gained fitness, she began jogging part of the way, then running the whole thing.

"I ran religiously," Stirling says. "Even if I had to get up at 5 on a freezing winter morning."

Now Stirling weighs 144 pounds, a healthy weight for her 5-foot, 10-inch frame. She has a new job and a happy relationship.

Hill's analysis of all 3,000 successful losers shows that they spend about an hour a day in moderate physical activity. Over the course of a week, that burns off about 2,700 calories -- or four Big Macs and a couple of Cokes to wash them down.

But then, successful losers don't eat Big Macs. Or French fries. Or cheesecake or fried chicken or bacon or fettucine alfredo.

Somehow, in a world that offers us an abundance of delicious high-calorie delights, they say, "No, thank you. Just the check."

How do they do it?

Weight loss experts -- not the ones you see on TV infomercials at 3 a.m. but the real professionals -- say things like belief and confidence have a lot to do with it. To keep weight off, you have to take responsibility for eating right and exercising in a world that encourages driving everywhere and super-sizing everything.

Taking charge of health

"You have to take a change of attitude where you assume responsibility for your weight," says Donald Williamson, a psychologist at Louisiana State University. "What people actually do to be responsible and accountable like this just differs all over the place."

Sally Dorsten did it by becoming a vegan. She eats no animal products at all, not even eggs or dairy.

"It was a radical life change," she says, but she found it easy, even enjoyable. She found plenty of cookbooks to help her construct healthy and nutritional meals from tofu, whole grains, sprouts and other ingredients that the typical American carnivore fears and avoids. It also helped that her husband supported and encouraged her dietary choice instead of "pooh-poohing" it.

Thanks to the vegan diet and increasing her exercise over the past seven years, Dorsten has lost 45 pounds.

"I feel like I'm 20 and I'm 57," she says. "I'll never change."

National Weight Control Registry data suggest she's right. After three to five years at a lower weight, Hill says, very few people regain the pounds they lost.

You don't have to swear off all things animal to be a successful loser, though. Kubacki, a Wall Street bond trader who weighs 30 pounds less than he did 20 years ago, acknowledges enjoying the occasional hot dog. But he has only one. In his opinion, the secret is to develop good habits and then have faith that sticking with them will improve your life.

"You have to really believe in it," Kubacki says.

Landau believed in it so much that she went to work for Weight Watchers, the organization that helped her lose 36 1/2 pounds a quarter century ago.

"I figured, well, I talk about it all the time," Landau says. "Why not get paid for it?"

As a meeting leader for Weight Watchers, she has seen countless successes and failures. Landau says the people who succeed are the ones who "take their watch off." Instead of worrying about how fast they'll lose weight, they concentrate on changing their lives for the better.

"It's taking control," she says. "Being in charge."