"It's my metabolism!"
Sound familiar? If you're carrying some extra pounds (and having a hard time losing them), it's
tempting to put the blame on a sluggish metabolism.
But is your metabolism really the reason it's often so hard to lose weight? And, more important, is
there anything you can do about it?
WebMD asked experts to explore facts and myths about metabolism -- and the good news is, there
are things you can do to help boost your body's calorie-burning power.
See How You Can Boost Your Metabolism
What Is Metabolism?
Your metabolism, experts say, involves a complex network of hormones and enzymes that not only
convert food into fuel but also affect how efficiently you burn that fuel.
"The process of metabolism establishes the rate at which we burn our calories and, ultimately, how
quickly we gain weight or how easily we lose it," says Robert Yanagisawa, MD, director of the
Medically Supervised Weight Management Program at Mount Sinai Medical Center in New York.
Of course, not everyone burns calories at the same rate.
Your metabolism is influenced by your age (metabolism naturally slows about 5% per decade after
age 40); your sex (men generally burn more calories at rest than women); and proportion of lean body
mass (the more muscle you have, the higher your metabolic rate tends to be).
And yes, heredity makes a difference.
"Some people just burn calories at a slower rate than others," says Barrie Wolfe-Radbill, RD, a
nutritionist specializing in weight loss at New York University Medical Center.
Occasionally, Yanagisawa says, a defect in the thyroid gland can slow metabolism, though this
problem is relatively rare.
And here's a fact that may surprise you: the more weight you carry, the faster your metabolism is
likely running.
"The simple fact is that the extra weight causes your body to work harder just to sustain itself at rest,
so in most instances, the metabolism is always running a bit faster," says Molly Kimball, RD, sports
and lifestyle nutritionist at the Oscher's Clinic's Elmwood Fitness Center.
That's one reason it's almost always easiest to lose weight at the start of a diet, and harder later on,
Kimball says: "When you are very overweight your metabolism is already running so high that any
small cut in calories will result in an immediate loss."
Then, when you lose significant amounts of body fat and muscle, your body needs fewer calories to
sustain itself, she says. That helps explain why it's so easy to regain weight after you've worked to
lose it.
"If two people both weigh 250 pounds, and one got there by dieting down from 350 and the other one
was always at 250, the one who got there by cutting calories is going to have a slower metabolism,"
says Yanagisawa. "That means they will require fewer calories to maintain their weight than the
person who never went beyond 250 pounds."
Make the Most of Your Metabolism
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Revving Your Engine
Though some of the factors affecting metabolic rate can't be changed, happily, there are ways to
maximize the metabolism you're born with -- even when you're dieting.
Among the best ways is exercise. This includes aerobic workouts to burn more calories in the short
term, and weight training to build the muscles that will boost your metabolism in the long run.
"Since muscle burns more calories than fat -- even while at rest -- the more muscles you have, the
higher your resting metabolic rate, which means the more calories your body will be burning just to
sustain you," says Kimball.
Personal fitness trainer Kelli Calabrese MS, CSCS, ACE, notes that every pound of muscle in our
bodies burns 35 calories a day, while each pound of fat burns just 2 calories per day.
While 30 minutes of aerobic exercise may burn more calories than 30 minutes of weight training,
Calabrese says, "in the hours following the cessation of exercise, the weight training has a longerlasting effect on boosting metabolism."
Having extra muscle also means you can eat more and gain less.
Adds Yanagisawa: "We don't tell people to exercise while dieting only to burn calories -- we also
know that exercise builds muscle and that is what will help you burn more calories and maintain the
weight loss you work so hard to achieve."
Some women fear they'll "bulk up" with weight training. But Calabrese, author of Feminine, Fit and
Firm, says not to worry.
"Women don't have the hormones necessary to develop those huge muscles, so you can feel good
about doing weight training," she says.
Eat More, Burn Better
Of course, the diet advice we'd all love to hear is "Eat more and lose more weight!" But what really
works is "Eat more often, and you'll lose more weight." Small, but frequent, meals help keep your
metabolism in high gear, and that means you'll burn more calories overall.
"When you put too many hours between meals, your metabolism actually slows down to
compensate," says Kimball.
If you then eat a huge meal -- at the same time your metabolism is functioning as if you're starving -your body wants to hold on to every calorie.
While this won't make much difference on an occasional basis, Kimball says, make it a way of life and
it can get harder to lose or maintain weight.
Kimball's advice is borne out by the findings of a study that was presented at the 2005 annual
meeting of the American College of Sports Medicine. Researchers from Georgia State University
reported that when athletes ate snacks totaling about 250 calories each, three times a day, they had
greater energy output then when they didn't snack.
The study also found that snacking helped the athletes eat less at each of their three regular meals.
The final result was a higher metabolic rate, a lower caloric intake, and reduction in body fat.
From supermodels who douse their food with red pepper, to movie stars who swear by green tea,
there's no shortage of claims for foods that are said to increase metabolism. But do any of them
work?
"Actually, any food will increase your metabolism, mostly in the first hour after you eat -- that's when
your system is most revved," says Kimball.
Further, she says, protein generally requires about 25% more energy to digest. So -- at least
theoretically - a high-protein snack might rev metabolism a little more than a carb-heavy food with the
same number of calories. That said, it's not clear that any food has special powers to boost
metabolism significantly.
"Some studies have shown hot pepper and very spicy foods can increase metabolism by about 20%
for about 30 minutes, but no one really knows if the extra burn lasts any longer than that, " says
Kimball.
In a small study on Japanese women published in the British Journal of Nutrition, researchers found
red pepper caused the body to heat up and revved the metabolism following a meal. But the most
effects were seen primarily when the red pepper was eaten with high-fat foods (which are also higher
in calories).
Another small study, published in the journal Medicine & Science in Sports & Exercise, reported that
male athletes who added red pepper to high-carbohydrate meals boosted both their resting and
active metabolic rates 30 minutes after the meal. But there was no evidence this burn power was
lasting.
The same appears true for green tea, which contains a substance called EGCG (epigallocatechin
gallate), a powerful antioxidant that some believe can bring about the same kind of calorie-burning
effect as hot pepper.
In a study of 10 men published in the American Journal of Clinical Nutrition, researchers found that 90
milligrams of EGCG and 50 milligrams of caffeine taken with meals boosted 24-hour energy
expenditure by 4% (caffeine alone did not show a similar effect).
But it's not clear whether this effect would be enough to boost weight loss. And that, says Radbill, is
precisely the point.
"Essentially, you would have to drink so much of it in order to see even a small effect, that I don't
think it's really worth it," says Radbill. "Drink green tea for other health-giving properties, but not to
lose weight."
The bottom line, she says, is this: "All these foods may have a slight impact on metabolism, but the
increase is still insignificant compared to what you need in order to lose weight."
Your best bet for keeping metabolism revved: Build muscles, snack on low-calorie, high-protein
foods, and keep moving!