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IN her
39 years, Claudia Hallblom has, by her own estimation,
lost and regained about 1,000 pounds. Her success at
losing weight was always driven by a goal, such as
looking nice for her graduation or wedding. Her tactics
usually included strict calorie-counting. But success on
the scales was always fleeting. Sooner or later, she
would revert to her old habits and no longer feel
motivated to change.
“I
didn’t know how to lose weight and keep it off,” the
Downey, California, woman says.
Most
people can lose weight. But few can maintain their new
weight for long. Researchers are now tackling that
problem, and what they’re learning is disconcerting. The
human body, it seems, is designed to sabotage weight
loss at every turn—once a body has been fatter, it wants
to get back to the weight that it used to be. Physiology
is cruelly changed in two ways: The body needs fewer
calories to maintain itself, but its craving for food is
more intense.
Making
sure the pounds stay off means pitting one’s willpower
against a swarm of biological processes involving the
brain, hormones, metabolism and fat storage.
“There
is a big shift toward understanding long-term weight
maintenance,” says Paul MacLean, associate professor of
medicine at the University of Colorado, Denver. “We have
a huge number of diet books and diet programs, and if
you do them, you can lose weight. The big problem is
keeping it off. The recent estimates are that 5 percent
to 10 percent of people are successful at keeping weight
off on a long-term basis.”
But
before you throw up your hands and reach for the
Twinkies, consider this: Scientists think that
understanding the stubborn biological processes at work
will lead to ways to fight back.
Exercise, it’s known, buffers the postdiet body against
regaining weight, in ways that researchers are just
starting to comprehend. Certain foods, scientists
believe, may help stave off weight regain, too. And
medications now in development target some of the
biochemistry thought to be linked to regaining weight.
“There
are strong physiological adaptations to weight loss that
promote weight regain,” MacLean says. “The good news is
we know a big part of the problem and why we haven’t
been successful over the past several decades.”
Human
biology—for obvious adaptive reasons—is designed to
protect against weight loss and potential starvation.
And after a period of obesity, the body may permanently
alter the way weight is regulated by more aggressively
stimulating appetite and signaling the body to protect
fat stores.
Metabolism has changed: the body now needs about eight
fewer calories per day for each pound of weight that was
lost. That means someone who loses 40 pounds will
require about 320 calories fewer each day than they did
before the weight loss. This difference in energy needs
before and after weight loss has been dubbed the “energy
gap” by University of Colorado professor James O. Hill,
director of the Center for Human Nutrition in Denver.
Appetite
hormones change, too. The hormone leptin, for example,
is a major appetite regulator—it tells the body to stop
eating and store fat after meals. Some people may be
genetically prone to having lower leptin levels, making
them more prone to obesity. But studies also show that,
after a weight loss, leptin levels are lower than what
they used to be. That means appetite is less easily
quelled.
Another
hormone, ghrelin, stimulates food intake—levels in the
brain fall lower after a meal. However, after a weight
loss, ghrelin levels in the blood generally increase,
and the fall-off after mealtimes isn’t as marked.
“You
lose 10 percent of your body weight. All of a sudden all
these systems kick in to try to keep you from losing
weight,” says Dr. Ken Fujioka, director of nutrition and
metabolic research at the Scripps Clinic in San Diego.
“People are mad at themselves or depressed after they
regain the weight. But I explain: It’s not you. Biology
has kicked in now.... You are hungry all the time. You
think about food all the time.”
The
brain isn’t the only thing acting to promote weight
regain. MacLean’s research suggests that the central
nervous system collects and interprets signals from the
intestines and peripheral tissues, such as fat stores in
the abdomen, to fight weight loss or regain pounds that
were lost.
The
weight comes back fast. “The entire system is saying,
‘Bring the calories in, store them efficiently and do
not reduce these signals until the fat is returned that
was there before,’” MacLean says. “You may look like a
lean person, but your body hasn’t changed inside.”
Moreover, animal studies show that most of the regained
weight is distributed as visceral fat, the abdominal
paunch that is linked to heart disease and diabetes.
So what
is a dieter to do?
There is
nothing we know of that does anything to reverse this,”
Fujioka says of the biological forces that defend body
fat. “It’s very tough.”
But it’s
not impossible. The National Weight Control Registry is
an honor roll of dieters who have fought and won.
Started in 1994 by Hill and Rena Wing, director of the
weight control and diabetes research center at Brown
Medical School, the registry now provides data on how
regular people have managed to keep weight off.
Based on
data from more than 7,000 people, Wing says there are
few similarities in how people lose weight. But those
who succeed in maintenance sing the same song.
Instead
of trying to eat less for the rest of their lives to
bridge the energy gap, these people exercise more.
Physical
activity, in ways that researchers don’t really
understand, influences some of the biological systems
that promote weight regain, encouraging the body to
become more sensitive to leptin and insulin, for
example.
“Everyone thinks exercise is about burning calories,”
Fujioka says. “But you are actually returning the system
to more like what it should be. Things start working
again.”
The
successful maintainers also change what they eat: The
registry found that they keep their calories in careful
balance with what they expend—religiously referring to
calorie charts and writing down everything they consume.
They also tend to eat low-fat foods.
But
there may be more nuances to food choices than that.
“We’re getting more interested in studies that look at
food composition,” Fujioka says. “It could be that
eating certain nutrients may also help the system work
better.”
Scientists don’t know how long it would take to return
the physiological responses of a once-obese body to
normal—or if, indeed, that ever is quite possible.
Studies
do show, however, that weight regain is most likely in
the first couple of years after weight loss.
“After
that, it’s as if you master the technique,” Wing says.
The
current research on obesity strongly points to two
messages that rely heavily on human behavior: Don’t gain
excess weight in the first place, and if you do, be
prepared to make permanent lifestyle changes to lose it
and maintain the loss.
Hallblom
finally lost 63 pounds over a period of 14 months by
adhering to Weight Watchers’ principles—such as learning
the nutritional content of food and keeping track of her
food intake—and taking up vigorous exercise.
She has
maintained her healthy weight for seven years and in
2001 was hired by Weight Watchers to improve its
services to Spanish-speaking clients in Southern
California. She says she wishes she had realized years
ago that maintaining a new weight required a very
different kind of lifestyle—forever.
“This
time,” she says, “I was ready to make permanent changes
to improve my life.” |
