WEDNESDAY, Nov. 2 (HealthDay News) -- Obese teens who want to lose weight may not be going about it in the most healthy or effective ways, according to new research.

Simply put, the researchers said, teens trying to drop the pounds don't seem to fully understand the link between exercise and calories. The analysis of nearly 44,000 adolescents who participated in the Philadelphia Youth Risk Behavioral Survey showed that, among the obese, girls who exercised still drank soda and boys didn't exercise at all.

In addition, three-quarters of the obese teens said they were trying to lose weight, but these were also the teens more likely to smoke, possibly as a weight loss aid, the study suggested.

U.S. childhood obesity rates have tripled over the past three decades, and nearly one in three children in America is overweight or obese today. The new study, slated for presentation at the American Public Health Association's annual meeting in Washington, D.C., sheds some light on why reducing these rates is such an uphill battle.

Obese girls who were trying to lose weight were more likely to engage in at least 60 minutes of physical activity each day, but they were also more likely to consume a sugary soda on a daily basis, which basically offsets many of the benefits of their daily exercise, said the study's author, Clare Lenhart, a public health doctoral candidate at Temple University in Philadelphia.

"Most of them are interested in losing weight and that is a positive, but the soda has enough calories to make up for all of those that they expended during physical activity," she explained.

Obese males who were trying to lose weight did not exercise and spent more than three hours a day playing video games, the study showed.

"If someone is obese and trying to lose weight, doctors need to ask follow-up questions to find out how they are going about it and give suggestions on how to modify their behaviors," Lenhart said.

Dr. Yolandra Hancock, a primary care pediatrician at Children's National Medical Center in Washington, D.C., said that adolescents are motivated to change, but there is a lack of education about how to do that in a healthy way.

"The study demonstrates a clear lack of understanding about how much calories are burned during exercise," she said. "To burn off the calories in one sugary soda, you need to run a mile, and most teenagers don't engage in that level of physical activity," Hancock noted.

"If an adolescent is trying to lose weight, it is important to ask them how they are going about it, because we may find out that there is lack of education about calories in and calories out," she added. "This is especially important in adolescents and teens because they are starting to make decisions for themselves in terms of what they will eat and how often they will exercise."

Hancock usually stresses the easy-to-understand 5-2-1-0 rule to overweight and obese teens who want and need to lose weight. This refers to five fruits and vegetables a day, two hours or less of screen time such as TV or video games a day, one hour of physical activity a day, and zero or very little sugar-sweetened beverages a day.

There is also room for compromise in this rule, she added. For example, "if an overweight or obese young man wants to play video games, they can play 'Just Dance' . . . or other active video games," she said. "There is a way to meet in the middle."

Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

First Lady Michelle Obama is spearheading an effort to end childhood obesity with her Let's Move campaign.