|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
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,
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
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
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.
The National Institutes of Health (NIH) — The
Nation's Medical Research Agency — is comprised
of 27 Institutes and Centers and is a component of
the U. S. Department of Health and Human Services.
It is the primary Federal agency for conducting and
supporting basic, clinical, and translational medical
research, and investigates the causes, treatments,
and cures for both common and rare diseases. For more
information about NIH and its programs, visit www.nih.gov.