The American metabolism is sputtering. This past summer, researchers at the University of Florida crunched stacks of government health stats on thousands of Americans and found that during the previous two decades, the number of prediabetics (people with blood sugar so high they may soon become diabetic) had risen from one in 10 to nearly one in five adults. The really startling part: This was among people of normal weight. While their waistlines were average, their metabolisms — the body's system for burning sugar — were stalling.
We may equate diabetes with obesity, but in an age when sitting slumped at a keyboard is the norm and our food supply is drenched in added sugar, even average-weight men who think they're active can be in trouble. "I had a guy come in the other day — normal weight, a jogger — and he said, 'I don't get it, I'm prediabetic?' " says Dr. Tim Church, a metabolism researcher at the Pennington Bio-Medical Institute in Baton Rouge, Louisiana. "I get it. He eats a ton of sugar, and he doesn't lift weights." Um, weights? What does that have to do with it? As it turns out, strength training is essential for a healthy metabolism, and it's the crucial piece that many of us may be missing.
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Step 1: Know the Basics
Think of your metabolism as an engine. You consume food, and your body breaks most of that fuel down into glucose (that is, sugar). The glucose travels through your blood stream to deliver energy to cells. At the same time, your body produces insulin, a hormone that delivers the glucose and helps ensure blood sugar doesn't get too high. The speed and efficiency at which this all happens is your metabolic rate.
The problem is that as we age our metabolic rate typically slows. Most see a drop of 1 to 2 percent a year, starting in their forties, a decline that drives many of the health woes of middle age. That's because a slower metabolism usually means more stored fat, which can cause an uptick in blood sugar, cholesterol, blood pressure, or inflammation, any of which can encourage even more fat gain. When all these issues occur at once, it's called metabolic syndrome, a condition that half of all Americans over 50 have — not so surprising when you note we also have serious sugar issues. About 14 percent of Americans are diabetic, with another 35 percent on the cusp as prediabetic. As Church says, "It's all interconnected."
Some of the problem can be explained by diet or, most important, carbohydrates, which break down to sugar in the blood. Church says a surprising number of guys he encounters are under the mistaken impression that because they jog or cycle a couple of times a week, they have a blank check to consume sugar-packed snacks and energy bars or a nightly dessert or cocktail (or three). For some, even "healthy carbs," like multigrain bread and whole wheat pasta, can overtax the body's ability to secrete insulin. Over time, flooding the body with sugary foods and drinks can exacerbate insulin resistance — a condition in which cells don't respond to insulin and sugar pools in the blood. This sets you up for diabetes, even if you're not overweight.
The other part of the equation is how you burn the sugar you take in, and here it's not a question of what you shouldn't be doing but what you should. This is where strength training comes in, because muscle is the primary place sugar is burned in the body. "Doing resistance training is like giving yourself a shot of insulin," says Dr. Jamy Ard, a weight management specialist at Wake Forest Baptist Health, in Winston-Salem, North Carolina. "You're getting the glucose from the bloodstream and into the muscles." We used to think that maintaining muscle strength was a quality-of-life issue — you wanted enough brawn to move your furniture or open a stuck mayo jar. Now exercise physiologists and weight-loss doctors regard muscle, and the exercise that pumps it up, as absolutely necessary to keep the metabolic engine running well as we age. "Muscle is the most metabolically influential tissue in your body," Church says. Each pound of it burns an average of seven to 10 calories daily, compared with just two or three calories burned by a pound of fat. For a good idea of how well your metabolism is firing, simply step on a digital scale at the gym and look for the readout of your lean muscle mass. More muscle equals more metabolic horsepower.
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Step 2: Get Stronger
Let's be clear: You do not have to be a meathead to have a healthy metabolism. You can keep yours fired by doing enough resistance work to hold on to the muscle you've got, says David Nieman, an exercise physiologist at Appalachian State University, in Boone, North Carolina. "The whole idea is to maintain as much muscle mass as possible as late in life as possible," he says. "Your metabolism will hang in there as a result." That said, you can speed your metabolic rate a little by putting on a few pounds of muscle now. Doing so will never be easier (your natural levels of testosterone and growth hormone are higher today than they'll be in, say, five years), and the added size will act as insurance for later. "A critical factor for muscle aging is reaching your peak possible development when you're younger," says University of Pittsburgh epidemiologist Anne Newman. In other words, create and maintain muscle mass now and you'll have more to lose when age-related muscle loss starts in your sixties and seventies.
There is another reason to dial up strength training sooner rather than later: to maintain the number of muscle fibers. Marcas Bamman, the director of the University of Alabama at Birmingham's Center for Exercise Medicine, has had success building the size of muscle fibers with his 60-and-older research subjects in several clinical trials. ("I can train a 65-year-old for four months and his fiber sizes match people 35 years younger.") But he's had no such luck boosting the number of muscle fibers, the other component of muscle mass. That's because muscles are a "demand-based system," Bamman says. If you're not stressing and training the fibers, some of them will begin to atrophy, disappear, and never come back. So if you've got 800,000 muscle fibers in a quadricep at age 30 (the number experts estimate) and you never strength-train, that number could fall 30 to 50 percent, potentially putting you at 400,000 fibers by the time you're 70. At that point, you can still build a stronger leg with the remaining fibers, as Bamman has demonstrated with his seniors. But your quad will never be as strong as it could have been — or burn glucose quite as efficiently — as if you'd strength-trained through your thirties, forties, and fifties.
Credit: Jerry Westergren / Getty Images