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 “Current recommendations of 150 minutes of
moderate-intensity exercise or 60 minutes of vigorous exercise per
week might not be sufficient to prevent long-term weight gain,” lead
researcher Trine Moholdt told Reuters Health in an email. “More is
needed.”
How much more remains an open question. Moholdt, from the KG Jebsen
Center of Exercise in Medicine at the Norwegian University of
Science and Technology in Trondheim, advocates as big a dose of
exercise as possible to stave off chronic illnesses and maintain
weight.
The Institute of Medicine, a nonprofit group that is the health arm
of the U.S. National Academy of Sciences, suggests normal-weight
adults spend an hour a day doing moderate-intensity physical
activity.
But the U.S. Department of Health and Human Services sets a lower
bar, recommending at least 150 minutes a week of moderate-intensity
aerobic activity for general health, though in prior research that
amount has failed to be sufficient for weight control.
The American College of Sports Medicine says at least 20 minutes of
vigorous-intensity exercise three days per week can also fulfill
exercise recommendations.
The guidelines were set as a goalpost for adults aiming to avoid
chronic illness, not to maintain weight.
Moholdt and her team studied the weight and exercise patterns of
more than 19,000 adults, assessing them three times over 22 years.
During that time, women gained nearly 19 pounds, on average, and men
almost 17 pounds.
Only those who exceeded the recommended weekly 150 minutes of
moderate-intensity exercise or 60 minutes of vigorous activity were
able to avoid significant weight gain over both the first and second
half of the study period, according to findings published in the
British Journal of Sports Medicine.
Even participants who reported getting more exercise than prescribed
gained weight, the authors write, calling some weight gain
throughout adult life “inevitable.”
“The study clearly shows we gain weight over time,” Dr. I-Min Lee
told Reuters Health. “If we want to slow the gain in weight, we need
to increase the physical activity.”
“People with the
largest gains in weight were the least active. Those with the
smallest gains were the most active,” she said. An epidemiologist
from the Harvard School of Public Health in Boston, Lee was not
involved in the current study but has done similar research.
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In a 2010 study, she found that middle-aged women who averaged
about an hour a day of moderate-intensity exercise successfully kept
off excess weight.
She described moderate-intensity exercise as walking briskly enough
to be able to continue a conversation but being unable to sing.
The National Weight Control Registry, which gathers information from
people who have successfully lost at least 30 pounds and kept it off
for a least one year, reports that 90 percent of its members
exercise, on average for about one hour a day.
In the U.S., where health experts predict half of adults will be
obese by 2030 unless lifestyle habits change, the Centers for
Disease Control and Prevention estimates that less than 48 percent
of adults exercise enough to improve their health.
In the current study, inactive women gained 12.5 pounds more than
women who exercised in excess of U.S. guidelines, and inactive men
gained nearly eight pounds more than their most active counterparts.
The research did not take participants’ diets into consideration.
Lee and Moholdt both stressed that any exercise is better than none.
“Everything counts,” Moholdt said. In another study, people who
reported doing just one sweaty exercise session a week lived longer
than those who weren’t active at all, she said.
“For weight-gain prevention, however, it seems that more is
required,” she said.
“If you’re heavy and you are physically active,” Lee said, “you
still are better off compared to someone who is overweight and not
physically active.”
SOURCE: http://bit.ly/1ioSX9J British Journal of Sports Medicine,
online April 29, 2014.
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