FRIDAY, July 15, 2005 (HealthDay News) -- Decreasing physical activity during adolescence seems to play a major role in weight gain among girls as they transition from children to women.
Inactive girls gained an average of 10 pounds to 15 pounds more than girls who were active between the ages of 9 and 19, according to a study appearing in the July 16 issue of The Lancet. The number of calories consumed increased marginally and did not appear to be associated with the weight gain.
"It does present a strong argument that physical inactivity in this age group is an important contributing factor to the development of obesity," said Dr. Robert Kramer, medical director of the Better Eating and Activity for Children's Health (BEACH) Clinic at the University of Miami School of Medicine. "Common sense has told us that that's probably true, and this does go a long way in validating that."
On the other hand, Kramer added, this study shows a correlation but it does not prove any cause-and-effect relationship.
"There could be other confounding factors that would explain why those girls who were least active are the heaviest," he said.
The American obesity epidemic is as troubling in youth as it is in adults. Results from the 1999-2002 National Health and Nutrition Examination Survey (NHANES) suggest that about 16 percent of children and adolescents aged 6 to 19 are overweight. Earlier, in the 1988-1994 period, NHANES estimated that only 11 percent in this age group were overweight.
A previous report had found that girls' recreational exercise declined between the ages of 9 and 19 by an average of 7.5 brisk, 30-minute walks each week.
The authors of this study logged changes in activity and in body mass index (BMI) for 1,152 black and 1,135 white girls in three parts of the country: San Francisco, Cincinnati and the greater Washington, D.C. area. The girls were also asked to fill out questionnaires on physical activity and food intake and all kept a diary on what they ate.
The researchers noted only small differences in BMI between "active" girls and "inactive" girls at the age of 9 and 10. (Active was defined as doing the equivalent of at least five brisk, 30-minute walks each week, while inactive was doing no more than 2.5 such walks weekly.)
In the following nine years, however, inactive girls had triple the gains in BMI and were about 10 to 15 pounds heavier.
Girls who described themselves as black tended to be heavier than those who described themselves as white. Black girls also consumed more calories. In addition, 32 percent of the white participants continued to be "active" through adolescence compared to 11 percent of black participants. At the same time, 58 percent of black girls stayed inactive compared with 28 percent of white girls.
According to the study authors, adding 2.5 hours of brisk walking each week could prevent this weight gain.
It is possible that the participants under-reported how much they were eating, the study authors admitted.
"It's pretty well acknowledged throughout the research and literature that self-reported food intake is generally underestimated," Kramer said. "It's certainly possible that caloric intake may be playing a greater part than this type of study indicates."
The authors also do not provide much detail on the macronutrient content of the girls' diets, Kramer pointed out. This also could be a factor contributing to overweight and obesity.
Still, the study does point to some obvious remedial measures.
"One would hope that when a study like this comes out that people can use it as a springboard to bolster the argument for physical activity," said Samantha Heller, senior clinical nutritionist at New York University Medical Center in New York City. "We have got to get our children moving."
According to Heller, providing a variety of fun, nonintimidating activities is the key.
"We need to have a variety of fun and interesting ways to motivate children and adolescents to move their bodies," she said. "And these programs have got to be in the schools because that's where children spend a lot of their time."
Parents, too, need to act as role models, she added.
"You can't tell your kid to go out and exercise while you're sitting in front of the television, not moving, eating a plate of cookies," she said.
More information
Visit the National Heart, Lung, and Blood Institute's We Can! program for ways to enhance children's activity and nutrition.
