Rev It Up: How to Reboot Your Metabolism

"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.

Originally published in FITNESS magazine, January 2012.