July 14, 2005 -- The growing time teenage girls spent on the phone or infront of the TV rather than on the playing field or at the gym may add up to anextra 20 pounds by the end of their adolescence, according a new study.
They say the results suggest that a drop in physical activity rather than asudden increase in calories may be fueling weight gain among teenaged girls andcontribute to childhood obesity.
Obesity is caused by an increase in calorie intake (eating more), areduction in energy expenditure (moving less), or both. But researchers saythat pinpointing the cause for the current rise in childhood obesity has beendifficult.
Less Exercise Leads to Weight Gain
In the study, researchers followed a group of nearly 2,200 black and whitegirls in three different U.S. cities from ages 9-10 to 18-19. Throughout thestudy, researchers measured the girls' body mass index (BMI, a measure ofweight in relation to height used to indicate obesity) and body fat, as well asmonitored their physical activity level and calorie intake.
The results showed the girls' physical activity levels significantlydeclined during adolescence while the number of overweight and obese girlsdoubled -- without a significant increase in their calorie intake.
Only about a third of white girls remained physically active throughouttheir teenage years compared with 11% of black girls.
Changes in physical activity scores significantly affected changes in BMI. Adrop in physical activity was associated with an increase in BMI.
They say the differences in BMI between physically active and inactive girlstripled between ages 9-10 and 18-19 years.
Inactive white girls experienced an average weight gain of 9 to 13 pounds,and inactive black girls gained an average of to 13 to 20 pounds.
In addition, the results showed that black girls were significantly heavierand fatter throughout adolescence than white girls. Their average calorieintake increased by an average of 120 calories per day by the end of the studywhile white girls' calorie intake was unchanged.
Staying Active May Fight Childhood Obesity
Researchers say their results suggest that programs to prevent the declinein physical activity experienced during adolescence may be effective tools inpreventing childhood and adult obesity.
For example, they estimate that increasing the girls' physical activity bythe equivalent 2.5 hours of brisk walking per week could prevent the weightgain experienced by the inactive girls.
In an editorial that accompanies the study in today's online edition ofThe Lancet, John J. Reilly of the University of Glasgow says thatincreased physical activity during adolescence would not only combat theepidemic of childhood obesity but it would also provide benefits in improvingchildren's bone and heart health.