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.
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.
|