30 years ago, the campers were mostly teenage girls, 100 pounds-plus overweight. The menu consisted of food like liver, fish and alfalfa sprouts, and the exercise was running and sit-ups.

The goal was to lose as much weight in as short amount of time as possible.

Now, things are a little less extreme: About 40 percent of the campers are boys. Most kids need to lose between 20 and 40 pounds. Menus offer a broader range of food, and exercise is downright fun, with activities such as tennis and kayaking. The camps emphasize healthy lifestyles and skills the kids can take home with them.

In short, so-called “fat camps” are more likely to resemble regular camps that just happen to specialize in teaching good decision-making techniques.

According to the Centers for Disease Control and Prevention, 16 percent of children ages 6 to 19 are overweight or obese в a number that has tripled since 1980.

The number of weight-loss camps has remained relatively the same, says executive director of the National Camp Association. There are about 15 to 20 out of a total of 10,000 camps in the organization. (Some camps have multiple locations.)

Who used to run Weight Watchers camps, says campers tend to be younger than they used to be. A large number of the 1,500 kids he expects will sign up for his three summer camps over the next few weeks will be between the ages of 7 and 12.

That age group tends to be more successful because parents have more input on the child’s eating and exercise habits, he says. Bad eating habits are also less ingrained in younger children.

And camps are all about building habits, not just handing out quick fixes. They offer classes about nutrition, portion control, emotional eating, and dealing with situations like pizza and ice cream parties.

“The biggest misconception about weight-loss camp is that they don’t serve you enough food and that they overwork you,” says Daniel, 15, who was featured in the MTV documentary “Return to Fat Camp” based on New Image Camp Pocono Trails in Pennsylvania. He lost 40 pounds at the camp. “It’s the exact opposite. They feed you the right amount of food and work you out just enough.”

Changing behavior is key to sustaining weight loss, says Ryan Craig, president of Wellspring, which runs 11 weight-loss summer programs around the world, including nine camps and two adult vacations, as well as programs at two boarding schools.

Wellspring participants learn to cook, shop, order at restaurants, and work with psychologists on stress management, frustration tolerance and emotional eating.

“It’s not a lack of information,” says Craig, referring to the reason kids are overweight. “They know what it means to be healthy. They’re resorting to food as an unhealthy coping mechanism.”

Some campers want to be there, as opposed to years ago when their parents made them go.

Rod Rezvani, 20, who at one point weighed 440 pounds, says his father suggested attending Wellspring Camp last summer. But, he says, it was “completely my decision.”

“I was happy I was finally making a change,” says Rezvani, who has lost 167 pounds and is enrolled in the Wellspring college program in Reedley, Calif.

Maya Murray, 8, of Long Island, N.Y., who was 112 pounds, attended New Image Weight Loss Camps last summer and came home 16 pounds slimmer, more confident and independent, and making healthier choices. She continued to lose weight, with her family’s support, and is now 76 pounds.

“I wanted to feel better and look better,” says Maya. “I couldn’t breathe that well. I couldn’t run fast. It was hard to be active.”

Wellspring makes sure that parents are part of the process, says Craig, offering family workshops the last two days of camp, a home-transition plan for each child and an after-care program.

Losing the weight does come at a price. New Image Weight Loss Camps cost about $1,100 a week; the camp does give out scholarships. Wellspring Camps cost about $5,950 for four weeks, but insurance covers some of that because of the therapy, says Craig.

Still, those costs may put some of these programs out of reach, especially for inner-city youth, who have higher rates of obesity.

There are cheaper options, says Susan Blech, co-author of the weight-loss memoir “Confessions of a Carb Queen” and the senior care coordinator at Brookdale Hospital’s childhood obesity program in Brooklyn, N.Y. She recommends parents look into schools or churches that run camps, sports activities or a program similar to hers, which is free.

The important thing is to keep kids active in the summer, says Madelyn Fernstrom, founder and director of the University of Pittsburgh Medical Center Weight Management Center.

Solomon also says more traditional camps are now focused on children’s fitness and health, serving more nutritious fare and encouraging lots of exercise.

“Any camp is great because it will force the child to have structured time in the summer,” Fernstrom says. “You want to choose a camp even if it’s a special camp like arts or science that has some activity.”