I kid you not.Actually, the new study by Johns Hopkins Bloomberg School of Public Health was conducted to investigate the role of exercise in teen obesity. The researchers found that the amount of teen exercise has remained stable over the past two decades, and thus concluded that the lack of exercise hasn't been the cause of the increase of obesity. Food consumption is the culprit. Except when you also take into account that the study found in 2007, only 34.7% of teens met federal physical activity recommendations, which call for activity strenuous enough to cause heavy breathing for a total of an hour a day for five or more days a week.
So, the study suggests that increased food consumption and lack of adequate exercise might both interact to contribute to teen obesity.Wow. Aren't you glad we have scientific research to explain this?
It's no surprise that obesity rates among U.S. youngsters have skyrocketed, tripling from 1976 to 2004. Public-health experts and obesity researchers attribute the trend in part to kids' increasingly sedentary lifestyles. As teens spend more and more time anchored before a screen — burning fewer and fewer calories each day — they're storing more of that unused energy as fat. Hence, the ballooning rates of obesity.
That's precisely why the findings of a new study by researchers at the Johns Hopkins Bloomberg School of Public Health came as such a surprise. The report, published last week in the journal Obesity Reviews, finds that the amount of physical activity among U.S. teens has not in fact changed significantly over the past two decades, even while that population has gotten heavier. "On the one hand, we have seen the obesity-prevalence increase, but we don't see a decrease in physical activity," says Dr. Youfa Wang, an associate professor at the Center for Human Nutrition at Hopkins and lead author of the study. "This suggests that physical activity is not a good explanation for the increase in prevalence of obesity."
In simple terms, body weight is a reflection of the balance between two variables: the calories a body takes in and the calories it burns off. As far as the average U.S. teen is concerned, the study suggests, the culprit behind weight gain is not a decrease in exercise but an increase in consumption. Of course, that doesn't mean teens are getting adequate exercise: Wang analyzed data from nearly 16,000 high school students between the ages of 15 and 18, who took part in the Centers for Disease Control and Prevention's longitudinal Youth Risk Behavior Surveillance Survey, about their physical activity. He and his team found that in 2007, only 34.7% of teens met federal physical activity recommendations, which call for activity strenuous enough to cause heavy breathing for a total of an hour a day for five or more days a week.
But the survey also found that teens' overall rate of daily exercise had not changed much since 1991, when the study sample was first asked to report their participation in gym classes in school and their level of physical activity at home.
So does this mean that exercise isn't important in controlling weight? As tempting as that conclusion might be, Wang and other health experts say that's not exactly what the new data show. The findings may say less about the role of exercise by itself than about the other variable in the weight equation — diet — and the interaction of the two.