Girls often become much less physically active during their teen years, but that's just when they should move into high gear if they want to control their weight, a new study reveals.

Scientists at Harvard Medical School in Boston analyzed national data on 3,914 females, ages 14 to 22. Information on the young women was gathered in 2001-2000 and again in 2003 and 2005. Some of the younger girls were gaining weight because they were still growing and maturing. However, most of the older girls had reached their full maturity and their weight gain was more likely to be unhealthy.

About half reported exercising at least once a week, and 14% said they exercised five or more times a week. The length of time and intensity of the activity varied dramatically, including doing short bouts of toning exercises, playing soccer, dancing, jogging. Among the findings, presented here at the annual meeting of the Obesity Society, an organization of weight-loss researchers and professionals:

•The young women gained an average of seven pounds between 2001 and 2005.

•The young women who exercised the most — five or more days a week — and limited their portion sizes gained about three pounds over four years compared to the seven-pound average.

•Those who exercised at least once a week and either ate a low-fat diet or limited their portion sizes gained about 5½ pounds.

Unfortunately, many girls tend to cut back on activity during puberty because they may not want to sweat or have their hair messed up in front of boys, and this is the worst possible time for young women to stop being active, says Alison E. Field, associate professor of pediatrics at Harvard Medical School and Children's Hospital, Boston.

Source: USA Today
http://www.usatoday.com/news/health/weightloss/2008-10-07-girls-teen-active_N.htm