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Metabolism Changes

Metabolism Changes

A Different Kind
of Energy Crisis

Remember when you could diet for a few days and drop an easy ten pounds? Well, nowadays it's not so easy. Oh, sure, you're eating less than you did back in your twenties and making a habit of passing on dessert and that mid-afternoon candy bar. But for some reason, you're a few dress sizes larger. And the pounds are piling on.

Here's what's happening: Your metabolism--how your body converts food into energy and then burns that energy as calories--is slowing down. This is a natural process that begins at about age 30. From then on, your body burns energy about 2 to 4 percent slower every ten years. So fewer calories are burned, and more are stored as fat. You can see that if you do nothing to counter this trend, you'll become heavier and less energetic. And you'll put yourself at greater risk for serious health problems such as high blood pressure and heart disease. Hardly a recipe for a youthful life.

Some of what's happening is beyond your control. You naturally burn calories slower than a man does. And your body also has a higher fat content than a man's, with your percentage of body fat inevitably increasing with time. "Metabolism changes are a direct response to changes in body composition," says Robert Kushner, M.D., director of the Nutrition and Weight Control Clinic at the University of Chicago. "As we age, we tend to lose muscle and gain fat. Since muscle burns a lot of energy, our energy needs diminish as we lose muscle, and our metabolism slows."

But most of this metabolic slowdown is our own doing. Yes, we lose some muscle as we age, but "the major cause of this muscle loss is inactivity," says Eric T. Poehlman, Ph.D., associate professor of medicine at the University of Maryland at Baltimore Department of Medicine. "The more inactive we become with age, the less lean muscle we have. The less lean muscle we have, the more inactive we become. Over the years, the two feed on each other, and our metabolism plummets."

How do you break out of this trap? Unless you have thyroid disease, which can play havoc with how your body burns energy, you can get your metabolism cranked up again by making some lifestyle changes. But first, here's what's going on inside.

Overfueled and Underactive

Add up all the energy needed to power the activities in a resting body--everything from breathing and digestion to the activity of nerve cells during thinking--and you have your basal metabolic rate, the minimum energy requirement you need to stay alive. For most women, this is about 1,000 to 1,200 calories per day.

Then add the calories you need to power your additional activities--everything from playing jacks with your kid to jumping jacks in aerobics--and you have the total number of calories you require every day.

This means, of course, that two women may have the same basal metabolic rate but burn very different amounts of calories every day. For example, a very active 125-pound woman can easily burn 2,200 calories a day, while a sedentary 125-pound type can barely burn 1,750.

Which takes us to the punch line of this brief lesson in calories--the metabolic formula for not gaining weight. Calories in must equal calories out. The calories that aren't "out" are stored in your body as fat. But if you burn more calories than you take in, stored fat is burned, and you lose weight.

So the way to not gain weight as you get older is simple: Cut back on calories. Pretend you like rice cakes. You know the routine. But there's a small problem. Your body doesn't know you're on a diet; it thinks you're starving to death. So instead of burning fat, your metabolism goes into famine mode, trying to preserve your fat stores.

"Very low calorie dieting can decrease your basal metabolic rate by 15 to 30 percent, making weight loss even more difficult," says Dr. Kushner. A very low calorie diet is one that consists of fewer than 600 calories a day. Because your body is trying to save you by keeping your fat level intact, it chooses another source of fuel: muscle. You've heard the phrase "Diets don't work." Now you know why.

Your metabolic rate doesn't return to normal after you stop dieting, because your body thinks another famine might be around the corner. Dieting actually prevents long-term, permanent weight loss.

And dieters typically add one more insult to metabolic injury: They cut calories without paying much attention to what kind of calories they're cutting. One gram of fat contains twice the calories of one gram of carbohydrates--and carbohydrates have the added benefit of burning faster than fats. So instead of cutting back on calories across the board, you'd be better off not cutting calories and maintaining a low-fat, high-carbohydrate diet that emphasizes fruits, vegetables, pasta and grains. "The fat you eat is much more likely to become the fat you carry," says Dr. Kushner.

Exercise: Your Metabolism's Best Friend

Okay, dieting isn't the answer. So what can you do when your age causes your body's metabolism to shift into a lower, slower gear?

Exercise.

Aerobic exercise--walking, riding a stationary bike, aerobic dancing, any activity that boosts your heart rate for 20 minutes or more--is the best way to burn calories. And the benefits of exercise just keep going and going. Exercise sets your metabolism at a higher rate, so calories are incinerated for hours after you've stopped.

But the best way to boost your metabolism is to participate in an aerobic activity and a regular period of a strength training, such as weight lifting. "The major reason one person burns 1 calorie per minute and another burns 1.5 is that the second person has more muscle mass, and muscle is an extremely energy-hungry tissue," says Dr. Poehlman. "Strength-building exercises such as weight lifting will add muscle mass at any age. And the more you do such exercises, the better for your metabolism."

To prove that point, Dr. Poehlman and his associates measured the basal metabolic rates of 96 people: 36 did aerobic activity, 18 did weight lifting, and 42 did nothing. The aerobic group had a 13 percent higher metabolic rate than the sedentary group; the strength group's metabolic rate was 18 percent higher than the sedentary group's.

This study, says Dr. Poehlman, shows that either aerobic exercise or strength training may provide a metabolic boost.

Maximize Your Metabolism

Convinced that exercise is the best way to beat the middle-age bulge? Here's what you can do to rev your engine.

Step up the pace. An easy way to burn more calories in the same amount of time is to put a little more speed into your current aerobic workout. Suppose you're a walker who covers a mile in about 15 minutes (about 4 miles per hour), burning roughly 365 calories per hour (or about 90 calories per mile). If you bump up your speed to a 12-minute mile (5 miles per hour), your calorie burn increases to about 585 for the same hour. That's a bonus of 27 calories a mile. That extra calorie burn each day can translate to a weight loss of about 15 pounds in less than a year.

Go longer. If you're already working out at your top speed, don't go any faster, but try to go longer. "Just like a car, your body will burn more fuel--in this case, fat--the longer it is engaged in an activity," says Dr. Kushner.

Work your arms and legs. Exercises that vigorously use both arms and legs are better fat burners than those that involve only your legs. "Cross-country skiing rates highest in lab tests for burning the most calories per minute because you're using your legs, upper body and even your torso," says Wayne Westcott, Ph.D., strength-training consultant for the International Association of Fitness Professionals. Stationary rowers and bikes with moving hand levers also rate high.

Start your day with breakfast. Experts say your body burns calories at a slower rate as you sleep. Breakfast acts as your metabolism's wake-up call, kicking it into the calorie-burning mode. If you don't eat something in the morning, you may ultimately burn fewer calories during the day. And it's more likely that when you do eat, you'll grab the first high-fat snack you see.

Spread out your meals. Eating small meals throughout the day instead of your standard three squares may be better for fat burning. After you eat, your body releases the hormone insulin, which causes your body to store fat. The larger the meal, the more insulin your body releases. But smaller, more frequent meals keep insulin levels lower and more stable. The less insulin you have in your blood, the more fat you burn, and the less you store.

Don't skip meals. Skipping meals and then eating one big meal at night can be a triple whammy, says Dr. Kushner. First, it puts you into a slow burn mode during the day. Second, the big meal provides an energy overload: The body can metabolize only so much food at one time, so the excess is likely to become fat. Third, most of the metabolizing will take place while you sleep--when your metabolic rate is at its lowest.

Exercise after you eat. A moderate workout right after a meal gives you a fat-burning bonus. A brisk three-mile walk on an empty stomach burns about 300 calories. But walking on a full stomach will burn about 345 calories. That's because eating gives your metabolism a boost; add exercise, and your metabolism gets a double boost and burns even more calories.

Spice up your life. Keeping an eye on your metabolism doesn't mean you have to give up tasty foods. In fact, hot, spicy foods such as mustard and chili may even shift your metabolism into high gear for a short period. In a study by British researchers, spicy food was shown to increase basal metabolic rate by an average of 25 percent.

Stay away from stimulants. Caffeine, alcohol and other stimulants may raise your metabolic rate, but once they're out of your system, your metabolism crashes back to normal or below. The wise move, says Dr. Poehlman, is to avoid any artificial means of raising your metabolism unless it's prescribed by a doctor.

Have your thyroid checked. An underactive thyroid causes the body to burn energy at a slower rate than normal, and an overactive thyroid has the opposite effect. More women than men have thyroid disease. So if you suspect yours is out of whack, have it checked by your doctor. If a thyroid hormone deficiency exists, it can often be regulated with prescription drugs.