More activity linked with less body fat in girls

By Joene Hendry

NEW YORK (Reuters Health) - Middle school girls who are more physically active have a lower percentage of body fat than their counterparts with lower activity levels, according to new study findings.

"An additional 11 minutes of brisk walking or similar activity as girls age from the sixth to eighth grade appears to attenuate increased body fat," lead author Dr. June Stevens told Reuters Health. "This provides strong evidence that active girls are healthier."

Much of the existing research among youth relies on body mass index, an imperfect measure of fatness, and self-reported measures of activity, which tend to be inaccurate, noted Stevens, of the University of North Carolina at Chapel Hill.

As an alternative, she and colleagues calculated body fat among 1,576 girls in the sixth grade, who were randomly selected from six middle schools in six different metropolitan areas across the country. The girls wore an accelerometer belt over a 6-day period to measure their daytime physical activity. The investigators repeated these measurements 2 years later in 3,085 eighth-grade girls.

"We purposely did not control for food intake but let girls live normally," Stevens said.

The researchers' findings, reported in the American Journal of Epidemiology, show the percentage of body fat was 2.64 points higher among sixth grade girls with the lowest levels of physical activity compared with those with the highest levels.

Sixth-grade girls who averaged 12.8 minutes of moderate-to-vigorous activity each day, compared with those who averaged 34.7 minutes, were 2.3-times more likely to be overweight. The investigators defined moderate-to-vigorous activity as brisk walking or more intense physical activity.

Furthermore, girls who increased their activity levels by 6.2 minutes per day between the sixth and eighth grade had a decrease in body fat that was nearly 0.3 percentage points lower than girls who decreased their activity levels by 4.5 minutes over the 2-year period.

The changes in percentage body fat were large enough to potentially make a public health difference, Stevens commented.

More community-based studies are needed to better understand what levels of physical activity prevent the development of obesity, the investigators conclude.

SOURCE: American Journal of Epidemiology, December 2007.