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Ten Truths About Metabolism

Posted 02-07-2008 at 09:17 PM by 2xmomma

By Lise Funderburg (from Oprah magazine - Sept2003)

You're doing everything right, and you're still not losing weight. Is
it your metabolism? Can you do anything to get your motor running

You dream of a metabolism so fast you could burn through a wedge of
chocolate cheesecake or a slab of lasagna just walking the dog. But
wake up and smell the science, honey. The nation's leading
researchers are about to reveal the hard, fast and slow truth about
our calorie-converting engines.

One: What is metabolism?

It refers to the amount of energy (calories) your body burns up in a
day. Sixty to 70 percent of your daily caloric expenditure goes into
your resting metabolic rate (RMR), the energy required to keep your
body functioning. People who eat like a horse and never gain weight-
said to have fast metabolisms-are born with high RMRs, meaning it
takes a lot of food for their particular bodies just to stay alive.

Two: How do you measure it?

The most accurate method uses large, indirect calorimeter machines in
labs or hospitals under strictly controlled conditions. New handheld
models are less precise, but they're an improvement over the widely
used Harris-Benedict formula, which calculates your metabolism based
on age, height, weight, gender and activity level. The Harris-
Benedict is less accurate the more overweight you are.

Three: How much can one person's metabolism differ from another's?

I***e, gender, height and body composition are the same, the
variation in resting metabolism is likely to be less than 3 percent,
according to Steve Smith, M.D., an Assistant Professor of
Endocrinology at the Pennington Biomedical Research Center of
Louisiana State University. For example, if two equally active 38-
year-old women are both 5'5" and weigh 130 pounds, one might have a
daily RMR of 1,800 calories and the other, 1,854 calories-an increase
that only buys the second woman about two walnuts per day.

Four: Do overweight people have slower metabolisms?

No. The opposite is usually true, because the more you weigh, the
harder your body has to work, says Pamela Peeke, M.D., Assistant
Clinical Professor of Medicine at the University of Maryland and
author of Fight Fat After Forty.

Five: Can you crank up your RMR?

Ah, the $64,000 question. Although the idea has been challenged in the press, our experts agree that replacing fat withlean muscle does speed up your RMR - just not by much. In fact, the effect of strength training may not be as dramatic, or attainable, as fitness coaches suggest.

The mucscles you build through strength training - the skeletal ones attached to your bones - determine only a small fraction of your RMR, says Claude Bouchard, PhD, a veteran obesity researcher and Pennington's executive director. Even if you pumped up your skeletal muscle by 15 percent - adding 11 pounds of muscle for a 154-pound person - you would only get about a 5 percent increase in RMR, which at the very most would mean 75 extra calories for someone eating 2,000 per day. The training required to achieve such an increase, however, is so intense, Bouchard says that hardly anyone would do it. To build a mere 5 pounds of muscle, says John Jakicic, PhD, director of the Physical Activity and Weight Management Research Center at the University of Pittsburgh, you'd have to lift heavy weights three days a week for at least six months - each time to the point of completely exhausting the muscles.
If you don't want to push yourself that hard, the good news is that to lose weight you really just need to get out and move - walk an extra mile, play softball, swim. Regularly. "People fixate on this resting metabolic rate, and that's crazy," Nelson says; they're barking up the wrong tree. "Boosting your RMR gives a subtle nudge to energy consumption rates, but increasing physical activity is a sledgehammer."

Six: Do the supplements that promise to speed up your metabolism

The boosters du jour-caffeine drinks and green tea-will increase RMR
by tiny amounts, Smith says, but even the controversial herb ephedra,
which has caused dangerous side effects, including death, will give
only a five to eight percent spike, maybe allowing you an extra third
of a candy bar.

Seven: Does metabolism slow as you age?

Yes, says Jeanine Albu, MD, chief of the Metabolism and Diabetes
Clinic at St. Luke's-Roosevelt Hospital Center. "For women, there's a
big drop with menopause." Miriam Nelson, Ph.D., Director of the
Physical Center for Activity and Nutrition, estimates that between
ages 40 and 80, an average person's RMR slows down by 25 to 30

Eight: Does yo-yo dieting permanently lower metabolism?

No, says Rudolph Leibel, M.D., Chief of the Division of Molecular
Genetics, Department of Pediatrics, at Columbia University College of
Physicians and Surgeons. "You can succeed and fail as many times as
you like without permanently affecting your metabolism."

Nine: How does dieting in general affect it?

Well… nature takes a cruel turn here. Programmed to withstand
starvation, our systems slow to conserve energy when we're not
getting enough fuel. "As soon as you restrict your calories, your RMR
goes down," says Nelson. Then, to add insult to evolutionary injury,
as your body gets lighter, it requires less energy to move and
maintain itself.

But don't give up: Instead, get up and go. Increasing your activity
level seems to decrease appetite, says Nelson. And even modest
resistance training can keep your RMR from dropping as you lose
weight by building, and helping you hold on to, your lean tissue
mass. You don't have to heft huge hunks of iron; reasonably strenuous
training with machines or bands, or activities like Pilates, should
work just fine.

Ten: Does metabolism really matter?

As far as weight loss goes, "the role of metabolism, RMR in
particular, has been overrated," Smith says. Richard Weil, Exercise
Physiologist at St. Lukes Roosevelt Hospital Center in New York,
agrees: "People are just not expending enough energy. If you drive
through McDonald's and eat your French fries in the automatic car
wash while you call a guy on your cell phone to mow the lawn for you,
you are never, ever going to lose weight." Rather than getting hung
up on the rate of your metabolism, concentrate on making it work for
a living. Ladies (and gents!), start your engines!
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