CHICAGO -- Paris Woods is hardly a poster child for the obesity epidemic. Lining up dripping wet with kids on her swim team, she's a blend of girlish chunkiness and womanly curves.

In street clothes, the teen blends in with her friends, a fresh-faced, robust-looking All-American girl.

That's the problem.

Like nearly one-third of U.S. teens, Paris Woods is overweight. Her doctor worries her weight will creep up into the obesity range. One out of four black girls her age is obese.

The more than 11 million U.S. teens who are overweight or obese face an increased risk for diseases once confined to adults, like diabetes, artery damage and liver trouble. Those problems, along with high blood pressure and high cholesterol, are showing up increasingly in kids.

Paris' pediatrician urged her to take part in an intensive experiment. The goal? To see if a yearlong program of weekly sessions with a nutritionist, exercise trainer and doctor, all preaching lifestyle changes, could keep the 14-year-old from becoming obese.

It's the kind of intensive help that the influential U.S. Preventive Services Task Force says can work for teens.

Through successes, setbacks and even a bout with swine flu, Paris tried sticking with it. Skipped sessions stretched the program from 12 months into 20, but she didn't quit.

Her experience is a reflection of many families' struggles with obesity.

The options in Paris' middle-class mostly black South Side neighborhood are limited to fast food. Paris has a taste for fried chicken, bacon cheeseburgers and candy, and sometimes little willpower. Swimming helps her fight. The sport has been a passion since she was a little girl.

Her parents, Dinah and Parris Woods, wanted their three daughters to be active, to keep them busy and out of trouble. "You can't just do nothing," says Dinah, 47, a former fitness instructor.

In Paris' 'tween years, her weight started to creep up. She developed early and classmates made fun of her. "They started calling me fat," Paris says, which made her self-conscious.

Paris' two college-age sisters ballooned into obesity in their teens. The family's pediatrician, Dr. Cathy Joyce, says that often happens. Teens put on weight, go off to college, and come back obese.

So she asked Paris to join an obesity prevention study at Chicago's Rush University Medical Center. Because shedding weight is tough if the people in charge of filling the fridge aren't on board, parents must enroll. Paris' parents are overweight and with borderline high blood pressure. They readily signed up.

That's unusual. Joyce has had a hard time recruiting. Her goal is 50 patients; she has only 31. Some parents aren't willing to change the family's lifestyle, others don't think their overweight kids are fat.

Joyce says parents often don't notice until teens are very obese. "Reality shows like 'The Biggest Loser' definitely have not helped," she said. They've skewed the public's perception of what overweight looks like, featuring people who are dangerously obese.

At 5 feet 4 inches and 158 pounds, Paris started the program about 20 pounds overweight. That was April 2008, just before her 15th birthday.

One of Paris' sisters had become a vegetarian, so the family decided to do the same. The hospital program doesn't require a specific diet, but recommends healthy grains, lots of fruits and vegetables, and avoiding unhealthy fats. Patients also are taught to read food labels and to eat three meals a day.

The idea is to choose a lifelong healthy way of eating.

It was all new to the Woodses, a tight-knit, busy family who used to skip breakfast and snack on the run.

Paris' mom likes to cook and the new regime lets her experiment with tofu, nuts and soy cheese. It also means shunning old family favorites, including mac and cheese. Their diet sometimes requires a trip to Whole Foods eight miles away, and it's costlier, but Dinah Woods says she'd prefer paying now, rather than later with her health.

The change was drastic, but also seemed exciting. Paris loved the avocado sandwiches and veggie burgers her mom packed for lunch, even if some friends turned up their noses.

At their weekly group sessions at Joyce's office, the Woods family weighs in and gets eating tips and encouragement from a nutritionist.

In the waiting room, there are half-hour workout sessions. Trainer Scott Mathews leads kids and parents through lunges, sit-ups, leg lifts and other exercises they're urged to do at home.

The Woodses usually come on Wednesday evenings. It's not a perfect time -- everyone's bushed after school and work. Dinah is a sales counselor and Parris, 46, a technician, attends night school. But they all roll out exercise mats.

Besides swimming most days, Paris likes to run with her two dogs, and tries to walk, instead of ride, when she can. Her parents walk a few miles several mornings before work. It's pretty easy to stick to the regimen during that first summer and fall.

By October, Paris' weight is down 8 pounds, to 150 and she's lost 3 inches from her waist. Her parents also have shed pounds, and all three say they have more energy.

Paris has lost her taste for meat. Thanksgiving is the first big test. No turkey, ham, biscuits or desserts like Dinah used to make. Instead, Paris says, it's "tofu everything," plus lots of vegetables. Could Dinah's lemon cake made with egg substitute possibly taste as good as her traditional desserts? "No, not really," Paris says laughing.

By mid-December, Paris felt really proud. She bought new pants and belts. And looking in the mirror, she says, "I don't see a face around fat. I just see, like, my bone structure ... my features in my face" are more visible.

Paris is starting to tell herself she looks pretty.

Still hovering around 150 pounds, she hopes to weigh 140 by her 16th birthday, April 13. "If I reach that, I'll be pretty happy," she says.

Chicago's 2008-09 winter is harsh, snowy and cold. Paris feels little motivation to venture outside to exercise. It's dark when she gets home from school and homework keeps her busy until bedtime.

Her friends alternate between encouragement and saying she's wasting her time.

By April 2009, it's clear Paris will miss her birthday goal. In fact, she's put on about 5 pounds. She says she's "getting a little tired" of the food.

Since they began a year ago, the family has missed some sessions due to busy schedules, but they've vowed to complete the program and are allowed several more months.

Then Paris is sidelined with swine flu. She skips a few more program sessions.

In summer, lifeguarding interferes. By the time she gets home, she's too pooped to work out. The fast food at the pool is tempting. She pushes the diet out of her mind.

There's no place to refrigerate lunches her mom packs. She skips doctor sessions; she knows she's gaining weight. She's disappointed in herself.

Looking back, she says, "It was horrible. ... I couldn't go back because I gained so much weight." But she returns to the medical center.

Fall 2009 is stressful. Dinah has to work long hours, arriving home too late to fix dinner. She and her husband still eat vegetarian. Paris does, too, at home, but eats fast-food away from home. Now a high school junior, she's stressing out over college admissions exams and studying for them.

When Thanksgiving arrives, it's another tofu turkey. But everyone falls off the wagon on a family vacation to Disney World after Christmas.

Finally, the Woodses' last program session arrives, Jan. 19, close to two years. Paris seems tense. She steps onto the scale: 170.6 pounds.

That's 12 pounds heavier than when she started. There are no tears, but she looks dejected and thinking "failure."

Dr. Joyce doesn't see it that way. She has overweight patients who weren't in the study who gained at least twice as much over the same time. The success is that Paris didn't become obese, and she looks far from it, even though she's four pounds from that.

Paris' dad gained a few pounds, too, but his waist shrank an inch. Her mom lost 6 pounds and 5 waist inches.

Joyce says skipped sessions might have been a factor; continuous professional feedback is motivating although too costly to last. A research grant paid for the Woodses to participate; otherwise the counseling and checkup sessions likely would have cost well over $4,000.

Paris' results show what everyone knew: Losing weight and keeping it off is tough, and life sometimes gets in the way.