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Rev It Up: How to Reboot Your Metabolism


What Affects Your Metabolism

I am lying on what looks like a cross between a jumbo Xerox machine and a tanning bed at the University of California, Los Angeles, Risk Factor Obesity Program as the big mechanical arm of a DEXA (dual energy X-ray absorptiometry) scanner moves over my head and then down to my feet. I came here to get the latest high-tech body-composition tests and to learn how fast my metabolism is.

Two minutes later a virtual relief map of the muscle, fat, and bone in my body starts to fill in on a computer screen.

"I never would've guessed," says Zhaoping Li, MD, PhD, the UCLA professor of clinical medicine analyzing my results, when she reads me the verdict: 40 percent body fat. As in obese. Except I'm a size 8. Here in Los Angeles, that alone can make you a plus size, but at five feet four inches and 148 pounds, I'm really just three or four pounds overweight.

To think that I had actually been looking forward to this visit. Me, the lucky girl who never dieted, never gained the freshman 15 and, until recently, never came close to being overweight. I chalked it all up to my speedy metabolism.

Electrodes are pasted onto my hands and feet for my second test, the bioelectrical impedance analysis. This one pegs my body fat at 32.7 percent, which, I am assured, is the better figure to go with. Translation: I'm not obese, just borderline unhealthy.

I am what is called skinny fat, explains David Heber, MD, PhD, director of the UCLA Center for Human Nutrition, who oversees the obesity program. "People can appear to be thin and fit, but their body fat is putting them at risk for diabetes, heart disease, and even breast cancer," Dr. Heber says. "A lot of models and actresses who don't exercise are actually skinny fat."

For the next eight weeks I would systematically follow the advice of leading scientists and trainers to reboot my metabolism. What I found out may be the key to keeping yours from ever flatlining.

What Affects Your Metabolism

I'm living proof that you can't judge a metabolism by its cover. You and I could be the same height and weight, have the same BMI, and even fit into the same J Brand jeans, but have wildly different flab-to-muscle proportions, making one of us the calorie-burning equivalent of a Bic lighter and the other of a blowtorch.

Metabolism, simply put, is the total number of calories your body burns each day. Sixty-five percent of those calories are used up for 24-7 functions like breathing and circulation­ — the top burners are your brain, liver, heart, and kidneys — with another 10 percent devoted to the process of digesting the very foods that may have given you that muffin top in the first place. The remaining 25 percent of the calories you burn can be chalked up to the physical activity you do in a day — not just Spinning class but every move you make, including standing in line or tweeting your latest DEXA scan results.

You've heard it before: The more muscle you have, the more calories you burn. In fact, lean tissues, including organs and muscles, on average burn 14 calories a pound a day, while fat only burns about three calories per pound, Dr. Heber says.

Simply put, whether you're Kate Moss or Kirstie Alley, it's the absolute amount of muscle in you that determines the overall speed of your resting metabolism — the amount you burn just sitting around — and some of us are born with an edge in the amount of muscle fibers we've got. But don't blame bad genes for your extra flab. "It's your environment — that is, food and activity — that is extremely important in ultimately determining your weight," says Andrew G. Swick, PhD, director of obesity and eating disorders research at the University of North Carolina at Chapel Hill Nutrition Research Institute in Kannapolis.

And there's plenty you can do to not only add muscle but also maximize your metabolism along the way.

Workouts and Diets for a Faster Metabolism

Workouts for a Faster Metabolism

Metabolism slows over time, but it doesn't do a sudden nosedive as you sit watching the American Idol finale. "Metabolism drops off 2 to 4 percent every decade as we tend to lose muscle mass," Dr. Heber explains. So, if as a twentysomething you burned 2,000 calories a day, fast-forward 10 years to your mid­thirties and you could be burning as few as 1,920 calories a day. Doesn't seem like a big difference until you do the math. Just 80 extra calories a day translates into eight pounds over a year, unless you pick up the slack with exercise.

"You can maintain your total energy expenditure as you age by combining strength training and aerobic activity. You'll probably need to do more of both," says Miriam Nelson, PhD, director of the John Hancock Research Center on Physical Activity, Nutrition, and Obesity Prevention at Tufts University in Boston. Nelson's studies in the 1990s found that a twice-weekly regimen of eight to 12 resistance exercises increased women's strength by 75 percent in one year, meaning they gained more metabolism-stoking muscle fibers. Most of those gains were in the first 12 weeks.

Even better, every workout you do will give you a metabolism boost, not just during it but also afterward. One study found that a 50-minute weight routine delivered an additional afterburn of 14 calories. Between sets, add cardio bursts or shorten the rest, and that afterburn spikes — to the tune of 25 calories following a quickie 19-minute circuit session, according to the same study.

I tested this myself by wearing a Bodybugg device on my right biceps as I followed the FITNESS "Your Best Body Ever" with trainers Justin Ghadery and Jeff Peel at 24 Hour Fitness in West Hollywood. The device's sensors track not only your movements but also things like body temperature to continuously record the number of calories burned during the day. The highest calorie-burn days occurred when I did the total-body circuits with Peel versus any other time I went to the gym.

I saw similar afterburn increases when I added speedier bursts to my steady treadmill workouts. Scientists have measured afterburn for a half-hour jog at 35 calories, as opposed to 75 calories for 20 one-minute sprints (with two-minute rests in between).

Not only that, but "high-intensity interval training is a quick way to ramp up your body's ability to use fat as a fuel," explains Jason L. Talanian, PhD, assistant physiology professor at Fitchburg State University in Massachusetts. In a study Talanian conducted, women who did interval workouts on a stationary bike, similar to Spinning, burned 36 percent more fat when they switched back to a steady ride the following week. The speed bursts sparked a 20 percent increase in the amount of mitochondria in the exerciser's muscle cells, making it easier for the women to metabolize fat for fuel rather than carbs.

To net the afterburn uptick, "push your speed for 30 seconds when you walk or run, and then return to your usual pace for 30 seconds," Peel says. Over the course of a month Peel has me increase the ratio so I get 30 seconds of slowdown time for every minute of intense exercise.

What to Eat for a Faster Metabolism

Having a lab test indicate you're made out of jelly could send a girl off on a juice-cleanse bender, but that would actually slow your metabolism. "If you're on a very low-cal regimen — in the 400- to 800-calorie-a-day range — metabolism falls by 15 to 20 percent," says David Nieman, PhD, professor of exercise science and director of the Human Performance Laboratory at Appalachian State University in Boone, North Carolina. Eating less than 900 calories a day also prompts your body to burn muscle tissue as well as fat, which lowers your metabolic rate even more.

Stick with the 1,200- to 1,500-calorie a day range, Nieman suggests, and you'll still slim down without taking such a big bite out of your metabolism. "What's more, about 90 percent of the weight you lose will be fat," he says, sparing more of that calorie-burning muscle.

Another metabolism no-no that women are guilty of is ditching meals, Neiman says. "If you skip meals, you put yourself on that path toward fasting, which signals the metabolism to slow way down," he explains.

Meanwhile, Dr. Heber warns me to get more protein to help preserve the lean mass that's my metabolism workhorse. He recommends the higher end for me: 100 grams of protein a day from such foods as white meats, fish, egg whites, and soy, ­starting with breakfast. "Studies show that people who eat a high-protein breakfast control their hunger longer and their weight better," says Dr. Heber, who is the author of sensible diet books, including What Color Is Your Diet? I promptly replace my cornflake habit with egg-white omelets and the occasional whey-powder-injected pancakes.

"Think of your body as a Ferrari," says trainer Ghadery when I tell him I've turned over a new leaf with protein. "You don't put cheap gas in a vehicle like that."

Measure Your Metabolism

Four weeks after my initial visit to the UCLA lab, I'm 10 pounds lighter, but more important is that my total body fat has dropped 5 percent, according to the DEXA scan. "We don't usually see any significant change in body composition until at least eight weeks," Dr. Li says, so the workout is working.

At my final appointment at eight weeks, I almost fist-bump Dr. Li when she tells me that of the 14 pounds total that I lost, nearly 10 of them were pure fat. "That is a lot," she says. But here's the kicker: Those other four pounds were a combination of water weight and muscle, meaning my resting metabolic rate went down from 1,150 calories a day to 1,117 calories a day.

"Normally when people lose weight that is muscle, their metabolism goes down; it's one of the factors that causes them to gain weight back," Dr. Heber explains. "By exercising, you maintained 97 percent of your resting metabolism. If you hadn't exercised, you would have lost 20 pounds, but up to half would have been lean mass."

Back at the University of North Carolina, Swick and other scientists are homing in on identifying the different genes responsible for energy expenditure, as well as phenotypes of people who don't gain weight from overeating, in the hopes of identifying the variables that make us fit as opposed to fat.

So the blueprint for a perfect metabolism is in the works, but I won't be sitting around for it. I've already learned my lesson: No more running low on muscle.

Do the Math on Your Metabolism

For a ballpark figure of how many calories you burn a day, multiply your weight by 14.

Use our BMR Calculator to get a closer estimate that also factors in your activity level

Measure Your Body Composition

Hitting the right weight is great, but also aim for a healthy body fat percentage to make sure there's some muscle to your metabolism.

Body Fat Percentage
Age Healthy Overweight Obese
20-39 21-32% 33-38% ≥39%
40-59 23-33% 34-39% ≥40%
60-79 24-35% 36-41% ≥42%

Body Fat Measuring Tools, Tested

Check out how real-world body fat tests rate.

Body Fat Scales
These home scales, like ones by Tanita ($50 and up,, use bioelectrical impedance analysis, but unlike instruments in a lab, they send currents through only the lower body rather than chest to toe. Still, they're a good measure of the change in readings between weigh-ins.

Skin-Fold Test
A caliper, or pinch device, measures the thickness of folds of skin in four key places where you store fat: the triceps, the suprailiacs (near the hip bones), the abs, and the thighs. Your best bet is to get two readings from a pro at the gym and take the average.

Bod Pod
As you sit inside the photo-booth-size Bod Pod for a few minutes, air displacement measures your body composition. Such clubs as Gold's Gym now use this device to get more accurate readings than with skin-fold tests.

"Why Can't I Lose Weight?"

If you've ever blamed a slow metabolism for your weight woes, we may be about to crack the code on the real culprit.

FITNESS sent 35-year-old broadcast media consultant Hillary Locke to the cutting-edge New York Obesity Research Center in New York City. There she spent all day and night in an airtight chamber as a scientist watched every move she made and morsel she ate to determine why this gym devotee and serial dieter couldn't seem to lose an ounce.

The result: Hillary's metabolism is not in fact slow but humming. She burned an impressive 2,397 calories in 24 hours — 540 during 60 minutes of riding the stationary bike and 30 minutes of toning exercises. She even lost a little more than a pound overnight!

So what gives with Hillary's three-year weight plateau?

The red flag was that she was burning mostly carbohydrates, even in her sleep, says Russell Rising, PhD, a nutrition researcher at the center. "The ratio of fat versus carbohydrates you burn should typically decrease during sleep to the point where you're burning more fat," Rising says. But readings of the carbon dioxide content in Hillary's breath, taken at night, indicated she was burning more carbs instead of fat.

Sure enough, Rising found that Hillary's diet while she was in the lab was 48 percent carbs, 41.8 percent fat, and 11 percent protein. He surmises that Hillary also probably eats a lot more a day than the 1,383 calories she ate in the lab and that her hectic travel schedule disrupts her sleep and, therefore, circadian rhythm, in turn affecting her ability to burn fat.

Hillary's next stop was to meet with Marissa Lippert, RD, the owner of Nourish Nutrition Counseling and Communications in New York City. Lippert advised Hillary to reduce her stress eating and make simple changes, like trading airplane pretzels for yogurt and limiting wine to one glass.

Within a week Hillary dropped three pounds.