Want to get your overweight child to lose weight, but don't know how?

Do the same thing yourself.

This is the main finding from a new study of 80 overweight or obese children and their parents. When parents lost weight, their kids did, too. For each one unit decrease in the parent's body mass index or BMI, children lost one quarter of a BMI unit.

"That is a lot of weight on a child," says researcher Kerri N. Boutelle, PhD. She is an associate professor of pediatrics and psychiatry at University of California-San Diego and Rady Children's Hospital, also in San Diego.

Since 1970, the rate of childhood obesity in the U.S. has tripled. About 1 in 3 children in America are overweight or obese. As a result, obesity-related diseases and conditions normally only seen in adults are increasingly diagnosed in kids.

To find out what helps children lose weight and what doesn't, Boutelle and colleagues looked at a number of factors. These included a parent's weight loss, changes in foods served at home, and parenting style such as setting limits on behavior.

The researchers divided the families into two groups. In one group, parent and child attended separate sessions in a five-month weight loss program that included dietary changes, exercise, behavioral change skills, and parenting skills. In the other group, parents were the only ones who participated in the weight loss program.

"The only thing that was associated with weight loss was parental weight loss," Boutelle says.

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The average BMI of parents in the study was obese, but not all the parents in the study were overweight. The findings may have been even more dramatic if all the parents were overweight or obese, Boutelle says.

"Children look up to their parents," she says. "It is not fair to tell a child to lose weight if you don't do it yourself."

It has to be a team effort.

Her message to parents? "Walk your own talk."

Nazrat Mirza, MD, is a pediatrician at the Obesity Institute at Children's National Medical Center in Washington, D.C. "This study reaffirms the role of the parent and the fact that changes need to be made in the home environment to be sustainable."

Studies have shown that only targeting parents for weight loss has trickle-down effects on kids. "The parents lose weight and the children do, too."

This makes perfect sense. "Parents are the role models for the children, they buy the food for the household, and set activity levels," Mirza says. "This is where the changes need to take place."

As a pediatric cardiologist, Steven Lipshultz, MD, often sees kids who have risk factors for heart disease largely due to their weight. He is professor and chairman of pediatrics at the University of Miami Miller School of Medicine.

If the parents are overweight and not on board, these children won't lose weight or make and maintain heart-healthy changes. "Less than 15% will go in the right direction, and we have to bring them in for a 12-week program that meets three times a week to encourage them to stay on track."

The new study "confirms good common sense."

The findings appear in Obesity.