U.S. Department of Health and Human Services
NATIONAL INSTITUTES OF HEALTH
NIH News
National Heart, Lung, and Blood Institute (NHLBI)


DECLINE IN PHYSICAL ACTIVITY PLAYS KEY ROLE IN WEIGHT GAIN AMONG ADOLESCENT
GIRLS

Girls who were inactive during adolescence gained an average of 10 to 15
pounds more than active girls, according to results of a 10-year
observational study of obesity. Total calorie intake increased only slightly
and was not associated with the weight gains. These new results show that a
previously reported steep decline in physical activity among adolescent
girls is directly associated with increased fatness and an increase of body
mass index (BMI), a measure of body weight adjusted for height.

The results of the Health and Growth Study, funded by the National Heart,
Lung, and Blood Institute of the National Institutes of Health, will be
published in an online edition of the "Lancet" on July, 13, 2005, and in the
July 23, 2005, print edition.

Study investigators previously found that girls' leisure-time physical
activity declined between the ages of 9 and 19 by an average of 7.5 brisk,
30-minute walks per week among all girls in the study.

At ages nine and ten, there were only small differences in BMI -- about 4 to
5 pounds -- between girls who were evaluated as "active" (doing the
equivalent of 5 or more brisk 30-minute walks per week) and those who were
"inactive" (doing the equivalent of 2.5 or less brisk 30-minute walks per
week). However, in the subsequent nine years of follow-up, the differences
widened, so that inactive girls had three times greater gains in BMI and
were approximately 10 to15 pounds heavier in the tenth year of the study.

"These results show that many girls are at a literal standstill when it
comes to exercise and physical activity in their pre-teen and teen years. As
parents, educators, and health care providers, we can do a lot to encourage
girls to continue physical activity throughout their adolescence, a step
that has been shown to help them maintain a healthy weight," said NHLBI
Director Elizabeth G. Nabel, M.D.

The study is a multi-center, longitudinal study of obesity development in
1,213 black and 1,166 white girls who were followed up annually from ages 9
or 10 to ages 18 or 19. The study took place between 1987 and 1998 in San
Francisco, Cincinnati, and the greater Washington, D.C., area.

Differences were noted between the black and white participants in BMI, food
intake and activity levels. Girls who self-reported their race as black were
consistently heavier than those who reported their race as white, their
calorie intake was higher, and increased with age. Thirty-two percent of
white participants maintained "active" physical activity status, compared
with 11 percent of black girls. Conversely, 58 percent of black girls
remained "inactive" compared with 28 percent of white girls.

At each annual study visit, BMI was derived from measures of height and
weight and skinfold measurements were taken to evaluate total body fat. Data
on physical activity and diet were collected from questionnaires and a
three-day food diary, recorded under the supervision of a nutritionist.

Study authors acknowledge that food intake is generally underreported,
especially among white girls and women. Dr. Sue Kimm, of the University of
New Mexico School of Medicine and the study's lead author, theorized that
"the phenomenon of under-reporting calories may have increased with the age
of the girls and may account for some of the largely unchanged dietary
patterns, especially among the white girls in the study."

Both black and white participants who maintained "inactive" status had 20
percent higher gains in BMI and an average of 20-40 percent increase in
skinfold thickness -- a measure of total body fat than girls who maintained
an "active" status.

"While 2.5 or more brisk walks per week is considered a modest level of
activity, increasing exercise by that small amount could potentially prevent
weight gain and serve as a goal for public health programs and schools, "
said Eva Obarzanek, Ph.D. NHLBI research nutritionist. "Just preventing the
decline in physical activity that currently occurs among adolescent girls
may be enough to prevent obesity."

The NHLBI has recently launched We Can! -- Ways to Enhance Children's
Activity and Nutrition -- a childhood obesity prevention program designed to
encourage parents and children to adopt healthy eating habits, increase
physical activity, and reduce leisure "screen time". More than 35
communities across the country are integrating We Can! lessons into health
programming for parents and kids.

NHLBI is part of the National Institutes of Health (NIH), the Federal
Government's primary agency for biomedical and behavioral research. NIH is a
component of the U.S. Department of Health and Human Services. NHLBI press
releases and other materials including information about obesity prevention
in youth are available online at www.nhlbi.nih.gov. The NHLBI's initiative
We Can! Provides resources for parents and guardians at
http://wecan.nhlbi.nih.gov.

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