March 23, 2010 -- Weight gain with age is common. But middle-aged women who
start out at a healthy weight and get in an hour of moderate activity every day
can avoid weight gain, according to a new study.
There is plenty of research on how to lose weight and keep it off, but
''there's very little research on preventing weight gain in the first place,"
says the study lead author, I-Min Lee, ScD, an associate epidemiologist at
Brigham and Women's Hospital and associate professor of medicine at Harvard
Medical School in Boston.
So her team addressed that question, trying to pinpoint the amount of
physical activity needed to prevent weight gain over time, without calorie
restriction, a question that is much debated with little consensus. The study
is published in the Journal of the American Medical Association.
Lee and her colleagues followed more than 34,000 women who had participated
in the Women's Health Study. The women's average age at the study start in 1992
Women self-reported physical activity and weight at the study start and at
years, 3, 6, 8, 10, 12, and 13.
All women ate a normal diet, and there weren't instructions to reduce
The researchers classified the women into three activity groups, depending
on the level of activity:
One group was active less than about 150 minutes a week -- the amount of
moderate intensity activity recommended for health benefits (but not
necessarily weight control), according to 2008 federal guidelines.
A second group was active more than 150 minutes a week but less than
The most active group got in 420 or more minutes a week of moderate
activity, or about an hour a day.
The researchers looked at physical activity and weight gain over intervals
averaging three years.
Exercise and Weight Control: Study Results
Overall, Lee says, all three groups gained weight over time -- an average of
But the more active the women, the less they gained. ''Compared to women in
the most active group, women in the two lesser active groups gained more
weight," Lee tells WebMD. ''Compared to the most active women, the two less
active groups were more likely to gain 5 pounds over the three-year period. The
second most active group was 7% more likely to gain the 5 pounds, and the least
active group 11% more likely."
The two lesser active groups were about equal, however, in the amount of
weight gained, she says.
Initially, Lee says, the relationship between physical activity and weight
control looked like it applied to everyone. But it did not.
Lee and her team also looked at a subgroup of women -- those who started out
at a healthy weight -- that is, with a body mass index or BMI of less than 25
-- and maintained a healthy weight throughout -- that is, gained less than 5
pounds at the three-year interval. Thirteen percent of the women, or 4,540, had
a BMI lower than 25 at the study start and maintained a healthy weight
throughout. ''We found the relationship between physical activity and less
weight gain held only for the women with a BMI of less than 25."