Rev It Up: How to Reboot Your Metabolism

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.

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

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.

Check out how real-world body fat tests rate.

Body Fat Scales
These home scales, like ones by Tanita ($50 and up, amazon.com), 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.