Lifting weights a few times a week might help us
stave off obesity, according to an interesting new study of resistance exercise
and body fat. It shows that people who regularly complete muscle-strengthening
exercises of any kind are about 20 percent to 30 percent less likely to become
obese over time than people who do not, whether they also work out aerobically
or not.
اضافة اعلان
The findings indicate that weight training could be more
consequential for weight control than many of us might expect, and a little
lifting now may keep us lighter, later.
The incidence of obesity in America is rising, with about 40
percent of adults currently meeting the standard criteria for obesity. That
number is expected to increase to more than 50 percent by the end of this
decade.
Unfortunately, few of us will drop any added pounds, long
term, once we gain them. Most people who shed more than about 5 percent of
their body weight regain it within five years.
The most effective way to deal with obesity, then, is
probably to prevent it. And regular exercise can help in that regard. Many
studies show that people who often walk, jog, cycle, swim or otherwise work out
aerobically tend to gain less weight with age than sedentary people and are at
lower risk of becoming obese.
But far less has been known about whether weight training
likewise influences weight. Some past research hints that resistance training
helps people retain muscle mass while people are trying to lose weight. But
whether it might also check long-term weight gain and avert obesity has not
been clear.
So, for the new study, which was published in June in PLOS
Medicine, researchers at Iowa State University in Ames, Iowa, and other
institutions, decided to look into the relationship, if any, between weights
and waistlines. They began by turning to the large and useful database compiled
for the Aerobics Center Longitudinal Study, a famous undertaking that had
tracked the medical, health and fitness status of tens of thousands of patients
who visited the Cooper Clinic in Dallas between 1987 and 2005. The men and
women had gone through extensive testing during repeated visits to the clinic.
Now, the Iowa researchers pulled the records for almost 12,000
of the participants, most of them middle-aged. None of them was obese, based on
their BMI, when they first joined the Aerobics Center study. (BMI, or body mass
index, indirectly estimates body fat, based on your height and weight.)
These particular men and women had completed the typical
array of health and fitness measurements during their visits to the clinic and
also filled out an exercise questionnaire that asked, among other issues, about
weight training. Did they ever engage in “muscle-strengthening exercises,” it
inquired, and if so, how often and for how many minutes each week?
The researchers then began cross-checking, comparing
people’s weights and other measurements from one clinic visit to the next.
Based on BMI, about 7 percent of the men and women had become obese within
about six years of their first visit to the clinic.
But BMI is a loose approximation of body composition and not
always an accurate measure of obesity. So the researchers also checked changes
to people’s waist circumferences and their body-fat percentage to determine if
they had become obese. By the yardsticks of a waist circumference greater than
40 inches for men and 35 for women, or a body-fat percentage above 25 percent
for men and 30 percent for women, as many as 19 percent of participants
developed obesity over the years.
Weightlifting, however, changed those outcomes, the
researchers found, substantially lowering the risk that someone would become
obese, by any measure. Men and women who reported strengthening their muscles a
few times a week, for a weekly total of one to two hours, were about 20 percent
less likely to become obese over the years, based on BMI, and about 30% less
likely, based on waist circumference or body-fat percentage.
The benefits remained when the researchers controlled for
age, sex, smoking, general health and aerobic
exercise. People who worked out
aerobically and lifted weights were much less likely to become obese. But so
were those who lifted almost exclusively and reported little, if any, aerobic
exercise.
The results suggest that “you can get a lot of benefit from
even a little” weight training, says Angelique Brellenthin, a professor of
kinesiology at Iowa State, who led the new study.
Of course, the study was observational and does not prove
that resistance training prevents weight gain, only that they are linked. It
also did not consider people’s diets, genetics or health attitudes, any of
which could affect obesity risk.
Perhaps most important, it does not tell us how muscle
strengthening influences weight, although it is likely that resistance training
builds and maintains muscle mass, Brellenthin says. A metabolically active
tissue, muscle burns calories and slightly increases our metabolic rate.
Interestingly, the desirable effect of adding muscle mass may also explain why
fewer lifters avoided obesity when the researchers used BMI as a measure. BMI
does not differentiate muscle from fat, Brellenthin points out. If you add
muscle with
weight training, your BMI can rise.
Still, the primary message of the study is that some weight
training likely helps, over time, with weight control.
“So, my advice would be to fit in a few body weight
exercises before or after your usual daily walk,” Brellenthin suggests.
Or join a gym or an online class. Or try one of Well’s easy,
at-home resistance-training routines, like the 7-Minute Standing Workout.
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