Less Exercise Behind Teen Girls' Weight Gain
Drop in Physical Activity in Adolescence May Promote Childhood Obesity
July 14, 2005 -- The growing time teenage girls spent on the phone or in
front of the TV rather than on the playing field or at the gym may add up to an
extra 20 pounds by the end of their adolescence, according a new study.
Researchers found a steep decline in physical activity during the teenage
years was largely responsible for weight gain commonly seen among adolescent
They say the results suggest that a drop in physical activity rather than a
sudden increase in calories may be fueling weight gain among teenaged girls and
contribute to childhood obesity.
Obesity is caused by an increase in calorie intake (eating more), a
reduction in energy expenditure (moving less), or both. But researchers say
that pinpointing the cause for the current rise in childhood obesity has been
Less Exercise Leads to Weight Gain
In the study, researchers followed a group of nearly 2,200 black and white
girls in three different U.S. cities from ages 9-10 to 18-19. Throughout the
study, researchers measured the girls' body mass index (BMI, a measure of
weight in relation to height used to indicate obesity) and body fat, as well as
monitored their physical activity level and calorie intake.
The results showed the girls' physical activity levels significantly
declined during adolescence while the number of overweight and obese girls
doubled -- without a significant increase in their calorie intake.
Only about a third of white girls remained physically active throughout
their teenage years compared with 11% of black girls.
Changes in physical activity scores significantly affected changes in BMI. A
drop in physical activity was associated with an increase in BMI.
They say the differences in BMI between physically active and inactive girls
tripled 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 heavier
and fatter throughout adolescence than white girls. Their average calorie
intake increased by an average of 120 calories per day by the end of the study
while white girls' calorie intake was unchanged.
Staying Active May Fight Childhood Obesity
Researchers say their results suggest that programs to prevent the decline
in physical activity experienced during adolescence may be effective tools in
preventing childhood and adult obesity.
For example, they estimate that increasing the girls' physical activity by
the equivalent 2.5 hours of brisk walking per week could prevent the weight
gain experienced by the inactive girls.
In an editorial that accompanies the study in today's online edition of
The Lancet, John J. Reilly of the University of Glasgow says that
increased physical activity during adolescence would not only combat the
epidemic of childhood obesity but it would also provide benefits in improving
children's bone and heart health.