Burning fat

Laurie Sears has done it all, from calorie-counting to fad diets to Weight Watchers. But this time the Denver resident says she's going to succeed, and she's willing to share her secret:

She's going to know her burn rate.

"I'm about to turn 50, and I'm going to go into it healthy," Sears said.

Few deny the importance of metabolism — or how quickly the body burns calories — in weight loss. And understanding how metabolism works can mean the difference between success and failure for the millions of Americans getting ready to start weight-loss plans, some experts say.

"It's enormously important," said Matt Hickey, an associate professor of health and exercise science at Colorado State University in Ft. Collins, Colo.

The first step is knowing the number of calories you burn daily without any activity. This is your "basal metabolic rate," or BMR.

Most people know at least one "fast burner" — someone who can single-handedly clear the party buffet table and not gain an ounce because of an unusually high BMR. That person might have a BMR of 3,500, compared with a buddy whose rate is 1,500.

For most people, BMR accounts for about 70 percent of calories burned. Movement, from talking to fidgeting to running, makes up the rest of daily calorie consumption.

To lose weight, the number of "calories in" per day must be lower than the number of "calories out." So the answer is to take in fewer calories or burn more calories, or both.

It sounds simple, but few people know the "out" side of this energy-balance equation, said Jay Kearney, vice president of clinical affairs for HealtheTech.

The Golden, Colo.-based company makes a device called the BodyGem, a hand-held mouthpiece that measures the oxygen flow in your breath to analyze your metabolic rate. The BodyGem is being used at a few Denver-area health clubs and is awaiting Food and Drug Administration approval for use by dietitians.

Now dietitians often follow the Harris-Benedict formula, which uses weight, height and age to estimate basic metabolism. "But it can be off as much as 500 calories," said Kearney, a former Olympic athlete. An inaccurate estimate could lead dieters to assume they're burning more calories, sabotaging their efforts to lose weight.

An inaccurate estimate could lead dieters to assume they could eat more calories than they should, fail to lose weight and give up, he said.