Metabolism

One of the most persistent myths about shaping up is that people who have trouble losing weight are simply cursed with a slow metabolism. But only in rare circumstances do you find someone with a medical problem, like a thyroid disorder, that keeps their metabolism slow.

'Creeping obesity'

For most Americans, a metabolic decline occurs over the years from causes including inactivity, excess fat, loss of muscle and dieting. But this metabolic drop—and the "creeping obesity" that results—isn't inevitable. Exercise and eating right can rev up your metabolic rate, which means your body will burn more calories—even at rest.

"The metabolic rate is a measure of how many calories your body needs to function." That rate is affected by age, gender, height, weight, activity level and food consumption. but "the biggest component is the amount of lean tissue (muscle, bone and organ mass) you have.

This is the one reason men typically have a higher metabolic rate—and lose weight more easily—than women. Men carry about 40 percent more muscle mass than women. Muscle contains special calorie-burning structures called mitochondria that convert calories to heat and water.

So when it comes to the decision on where the calories go in the body, the more muscle you have, the more calories are directed to the muscle cells to be burned and the less fat cells to be burned stored.

How dieting defeats you

Dieting slows the metabolic rate, partly by robbing the body of muscle. When you severely restrict calories, the body wants to conserve fat stores so it breaks down muscle mass. Also, dieters often skip lunch and/or breakfast and wind up overeating at night, when metabolism slows down and the body is in "fat storage mode."

By contrast, exercise boosts metabolism by burning fat and building muscle. The metabolic rate rises during physical activity and stays elevated for several hours afterward, says kris Berg, professor of exercise physiology and physical education at the University of Nebraska at Omaha. "This means a nice little chunk of added calorie burning," says Berg, who estimates that exercisers burn 5-7 percent more calories during the post-workout period.

Two kinds of exercise are critical: consistent aerobic workouts to boost the metabolic rate and strength-training workouts to build the muscle that elevates metabolism. Over time, combining aerobic and strength training exercises with sensible eating will cause your metabolic rate to rise and your body weight to drop to the lowest level it can naturally maintain, these experts say. They offer the following tips:

• Exercise regularly. Perform an aerobic activity for 30 to 45 minutes, four to five times per week., and do strengthening exercises two to three times per week.

• Eat enough to fuel your body. Restricting calories by more than 500 daily prompts the body to go into "conservation mode" and slows metabolism.

• Cut fat from you diet for weight loss. DJ recommends a diet that is 50 percent carbohydrate, 30 percent protein, and 20 percent fat.

• Add as much activity to your day as possible. Taking the stairs, parking far away—even getting up to change the TV channel instead of using the remote—boosts your caloric expenditure and helps rev up your metabolism.

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