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The power of lifting weights

It's easy to blame added flab on a slow metabolism. But there's a sure way to rev up the body's ability to burn fat: Build muscle.

October 28, 2002|Carol Krucoff | Special to The Times

One of the most persistent myths about weight loss is that people who have trouble shedding fat are simply cursed with a slow metabolism.

"Metabolism is everyone's favorite scapegoat," says William Evans, director of the Nutrition, Metabolism and Exercise Lab at the University of Arkansas for Medical Science.

Yet the metabolic rate -- a measure of how many calories your body needs to function -- is rarely responsible for weight-loss woes. "The metabolic rate is remarkably similar in most individuals," Evans says, once you control for these two critical factors:

Lean body mass, the percentage of body weight that comes from muscle, bone and organ.

Restrictive dieting, consuming significantly fewer calories than you expend.

Arguably the single most important determinant of metabolic rate is lean body mass. "The more lean tissue you have," Evans says, "the higher your metabolic rate."

Muscle mass boosts metabolism because muscle is active tissue that helps convert food into water, heat and energy. Fat is more passive, acting primarily as a stored form of body energy. So when your body is deciding what to do with the food you've eaten, the more muscle you have, the more calories it can send to muscle cells to be burned. This leaves fewer calories to go to fat cells to be stored.

Their higher proportion of muscle explains why, in general, men have higher metabolic rates than women and younger people have higher metabolic rates than older people. Starting around age 30, muscle mass in sedentary individuals declines by about 2% to 5% per decade, says Evans, adding that caloric requirements -- and metabolic rate -- decline accordingly. This is why an active, muscular 20-year-old can eat much more than a sedentary, pot-bellied 55-year-old without gaining weight.

Dieting also can ratchet down metabolism. "When you go on a restrictive diet, your body senses starvation and slows your metabolic rate to conserve energy," Evans said.

As your body tries to save its fat stores, it breaks down muscle mass for energy. This means that people who try to lose weight exclusively through extreme diets also rob their bodies of muscle and bone. This reduction in muscle further lowers the metabolic rate. Then, when these people go off their diets and gain the weight back, which is what typically happens, the regained weight is usually fat. This spiral of muscle lost and fat regained is common, Evans says, among people who try to lose weight solely by restricting calories.

But muscle loss -- and the resulting metabolic slowdown -- isn't inevitable. Strength-training exercises can help build and maintain muscle mass, dramatically "revving up" the metabolism. "Every pound of muscle we lose lowers our metabolic rate by about 30 to 50 calories per day, and every pound of muscle we gain raises our metabolic rate by about 30 to 50 calories per day," says Wayne Westcott, author of books and journal articles on strength training and fitness research director at the South Shore YMCA in Quincy, Mass.

"What's remarkable is the change you can make in your metabolic rate with strength training," he adds. "Several excellent new studies suggest that formerly sedentary adults who do a program of strength training for three months gain about 3 pounds of muscle -- that's a pound of muscle a month."

Researchers found that this 3-pound increase in muscle mass boosted the participants' resting metabolic rate by about 7%, Westcott says. "So with just three months of strength training you can reverse decades of the aging process."

Although growing older does cause some reduction in the metabolic rate, Westcott, Evans and others say that most of the metabolic slowdown attributed to aging comes from the physical slowdown. Genetics also plays a role but Evans says its primary contribution is "to the extent that your genes help dictate how much lean body mass you have." In rare cases, a medical condition, such as a thyroid problem, can affect the metabolic rate.

Although it's possible to boost the metabolic rate by artificial means -- such as cigarette smoking and certain drugs -- the risks far outweigh the benefits, Evans says.

Nicotine and compounds containing ephedrine stimulate the central nervous system, which releases certain hormones that help speed up the metabolism. "But the dangers of these drugs are becoming well known," he says.

Aerobic exercise is helpful for burning calories and improving cardiovascular health, Evans says, but strength training is the key to revving up metabolism. "Strength training builds the muscle that boosts the metabolic rate," he says. "And the higher your metabolic rate, the more calories you burn throughout the day -- even at rest."

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