Scientists say the childhood obesity epidemic in this country has to be halted. If not, the health of millions of American young people will be jeopardized.

Currently, one-third of U.S. children and teens — about 25 million kids — are overweight or obese, increasing their risk of developing diabetes, high cholesterol and other health problems.

Last weekend, weight-loss researchers presented dozens of studies on children at the annual meeting of the Obesity Society. We asked several top researchers to share their best advice to parents.

INVEST IN A STAIR STEPPER TO GET YOUR KIDS OFF THE COUCH

To get kids off the couch, parents should invest in a portable stair stepper ($70 to $110) for their children to use while watching their favorite shows, says James Levine, an endocrinologist at Mayo Clinic in Rochester, Minn., who has studied differences in how much kids and adults move during the day.

"This is so simple. We're not talking about joining the gym or redesigning your home. We're talking about getting a stepper and replacing the chair with it."

He bases his recommendation on a new study in which he and colleagues had 15 normal-weight and overweight children, ages 8 to 12, wear sensors that measured their posture and physical activity for 10 days. They found that the normal-weight kids stood and moved for an average of 368 minutes a day; heavy kids for 282 minutes. That's an 86-minute difference.

"It's a significant difference," says lead researcher Lorraine Lanningham-Foster, a senior research fellow at Mayo.

"It's quite staggering and reflective of what we see in adults," Levine says. Other work by these researchers shows that overweight people sit about 2 1/2 hours more a day than normal-weight ones.

Some folks do a lot more puttering, pacing and standing than others. Animal studies suggest some may be "hard-wired" to be more active than others, Levine says.

Levine believes this may apply to people too. Some seem to be programmed to do more standing, walking and cleaning while others aren't hard-wired to move much at all.

"The fact that these behaviors differ very early doesn't mean they are unchallengeable," he says. "But it does suggest that the wiring is in place very early in life."

LOW-CALORIE SUBSTITUTES IN FAVORITE MEALS

Parents can shave calories from kids' favorite meals without their children noticing, two nutrition experts say.

Researchers at Pennsylvania State University fed children, ages 2 to 5 1/2, two different types of macaroni and cheese. One was lower in fat; the other was made with extra butter and oil. The kids liked both dishes equally, but they ate 72 fewer calories with the lower-fat recipe. "That's a big reduction in calories for kids," says nutrition researcher Barbara Rolls.

"If parents are concerned about their child's weight, they should use less fat in their cooking," Rolls says. And they should add more vegetables and fruits when possible. Keep vegetables "relatively naked," that is, don't put heavy cheese sauces and margarine on them, she says.

In another study, children ages 5 and 6 consumed far more calories when they were served a very large portion (2 cups) of a high-fat macaroni and cheese than when they were offered about half as much of a lower-calorie version; 224 calories versus 117, says Jennifer Orlet Fisher, an assistant professor in the pediatrics department at Baylor College of Medicine in Houston. "Most children did not finish the smaller portions of the mac and cheese, suggesting their intake of the larger portions was excessive," she says.

Parents should let kids participate in serving themselves and encourage them to take smaller portions and then go back for more if they're still hungry, Fisher says. "Kids learn to like what is familiar to them. Parents can keep calories in check by getting into the habit of using low-fat cheese and less butter to make those kid favorites like mac and cheese," she says.

OFFER THE BEST FOOD OPTIONS

Who says kids don't listen when adults dish out good advice?

Researchers at Yale University had cafeteria personnel at an elementary school ask students going through the lunch line, "Would you like fruit or juice?" The students not only took the produce and juice, but they also consumed almost all of it.

"Parents need to be more authoritative and clearly let children know that a balanced meal includes a fruit and vegetable serving," says Marlene Schwartz of the Rudd Center for Food Policy and Obesity at Yale.

"The key is to put the foods you want them to eat right in front of them, rather than waiting for them to request the food, or even asking if they would like it," says Schwartz.