Diets Don't Work Long-Term

even though most people would
find that 41% number to be pretty depressing," she says. "We have
strong reasons to feel that this number underrepresents the true number of
participants who gained back more weight than they lost."

Mann and colleagues report their findings in the April issue of American
Psychologist.

Problems With Diet Studies

Diet studies, Mann and colleagues found, more often than not have one or
more problems:

• Most of the studies didn't actually weigh the dieters -- they simply asked
  them about their weight. "If you ask people their weight, they are going to
  give you a lower number than their real weight. That is obvious to anyone who
  ever applied for a driver's license," Mann says.


• In many of the studies, a substantial number of subjects dropped out of the
  study. "This isn't rocket science," Mann says. "A major reason
  people don't stay in touch with diet researchers is that they are embarrassed
  because they gained back the weight they had lost."


• Diet isn't the only thing study subjects did to lose weight. Most studies
  included exercise regimens. So any weight loss could have been due to exercise
  and not to diet.


• Many people in diet studies lost weight, gained it back, and went back on a
  diet before the end of the study. Such patients would be counted as having
  long-term weight loss when they simply lost weight only for a short period of
  time.

"When you keep to a reduced-calorie diet, your body makes metabolic
adjustments that make it harder and harder for you to lose weight," Mann
says. "Your body becomes very efficient, and you have to eat less and less
to continue to lose weight. If you had the will to go on a diet, the fact that
it steadily becomes less and less effective makes it even harder to stick to
it."

That's true, agrees Madelyn Fernstrom, PhD, founder and director of the
Weight Management Center at the University of Pittsburgh and diet and nutrition
editor for NBC's Today show.

But Fernstrom worries that people will get the idea from this that their
diets don't matter. And she's worried even more that the Mann report will
discourage people from trying to lose weight.

"'Diets don't work' is only half the story," Fernstrom tells WebMD.
"Lifestyle change will work if you have realistic expectations, good
support, and choose a plan that you can stick with -- a plan that will give you
moderate change over a long time."

That doesn't mean weight loss is easy. There's a myth, Fernstrom says, that
normal-weight people can eat anything they want and don't need a strict
exercise regimen. But that's true for only a very small number of people. Most
people who have a healthy weight have to work at it.

"It is really hard to lose weight, and it is even harder to keep it
off," Fernstrom says. "You can't cry about this. You must maintain
hope. We just have to develop better strategies to keep people on
track."

How to Lose Weight for Good

The basic problem is that people think diets are something you do for a
little while before going back to your old lifestyle, says obesity expert Rob
M. van Dam, PhD, assistant professor of medicine at Harvard Medical School.

"A lot of people go on a low-calorie diet for a few weeks and expect to
lose a lot of weight," van Dam tells WebMD. "But if you do a crash
diet, you will only regain the weight."

If you take medicine to control high blood pressure or high cholesterol, van
Dam says, you would expect your blood pressure or cholesterol level to go back
up when you stopped taking your medicine. A weight-control die works the same
way for obesity.

Why is it so hard to lose weight? A big part of the problem, van Dam and
Fernstrom say, is that people try to diet in isolation.

"Diet is affected by social issues, by what you do when you are with
your family and your friends," van Dam says. "In the current American
setting, which really encourages unhealthy eating and dietary patterns, it is
difficult to keep these lifestyle changes going."

Fernstrom says it's high time that America treated obesity like the medical
problem it is.

"We have to change as a nation and as a culture," she says.

One change she'd like to see is insurance coverage to pay for the cost of
professional assistance with lifestyle change.

"My patients tell me every single day they can't believe that lifestyle
change isn't covered by insurance but weight loss surgery is," Fernstrom
says.

Meanwhile, Fernstrom says, people who want to achieve and maintain a healthy
weight should start working at lifestyle changes they can maintain -- even if
it means not losing weight, but just staying at the same weight.

Elements of this lifestyle change, she says, include moderating food intake,
increasing physical activity, managing stress without food, and getting
treatment for depression and other illnesses that get in the way.

Even though diets don't work all by themselves, Mann agrees that there's
much people can do.

"I am not saying 'Don't diet' -- I'm just saying people should try to
eat healthy food in moderation and exercise like mad," she says.

By Daniel DeNoon
Reviewed by Louise Chang
B)2005-2006 WebMD, Inc. All rights reserved