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From the Desk of Clarence Bass

The Metabolism Myth

There's no biologic reason to get fatter as you grow older

You've heard people say it, maybe you've even said it yourself: "At about 35 my metabolism slowed down, and the fat started to accumulate." The clear inference is that a slowing of metabolism is inevitable, like night follows day. That's simply not true. Men and women, on average, do suffer from creeping obesity; in the Western world, the average 35-year-old male gains about a pound of fat each year until the sixth decade of life. Women often gain proportionately more. The reason, however, is not an aging metabolism.

One Criterion
Energy requirement of muscle remains constant

Exercise Physiology, the excellent textbook by Drs. William D. McArdle, Frank I. Katch and Victor L. Katch (Lea & Febiger, 3rd Edition, 1991), tells us that people do tend to get fatter with age. College-age men average 15% bodyfat and older men are usually about 25%. Women in their youth carry bodyfat about 25% and move up to 35% or more by age 50. The doctors hasten to add, however, that these "average" values should not be accepted as normal. "We believe that one criterion for what is considered 'too fat' should be that established for younger men and women - above 20% for men and above 30% for women. There is probably no biologic reason for men and women to get fatter as they grow older." Increases in bodyfat, they explain, are more a function of activity than age. Inactivity results in loss of muscle. And loss of muscle, not an aging metabolism, is the primary cause of creeping obesity. The muscle that remains is as metabolically active as ever.

Here are the facts as presented by Lawrence E. Lamb, M.D., in his book The Weighting Game (Lyle Stuart, 1988) [see our recommended book list]. Researchers led by Dr. Ancel Keys at the University of Minnesota measured the energy requirements of people of different ages with different amounts of bodyfat. They found that the energy requirement of fat-free body weight (weight of the body minus the bodyfat) were remarkably constant for both men and women between the ages of 20 and 60. All the subjects, no matter what their sex or age, burned about 1.28 calories per hour per kilogram (2.2 lbs.) of fat-free body weight, under resting conditions.

To really understand what's going on here, we need to define "metabolism." Metabolism is the chemical and physical processes in the body that build and destroy tissue and release energy, thereby generating heat. Our metabolism speeds up when we exert ourselves, and we burn more calories. Our metabolism slows down when we are at rest, and we burn fewer calories. But even at rest, it should be emphasized, we continue to expend calories.

It's The Muscle
Reduced muscle mass causes slowing metabolism

It's true: metabolism usually falls with age. In other words, older people on average burn fewer calories per pound of bodyweight than do younger people. But that's because their lean body mass is less.

William Evans, Ph.D. and Irwin H. Rosenberg, M.D. confirm this in Biomarkers, their landmark book about controlling the aging process (Simon & Schuster, 1991) [see our recommended book list]. If you have a reduced amount of muscle, as most middle-aged people do, your metabolic demand for oxygen and your caloric needs decline. That's because muscle tissue is active tissue requiring nourishment. Fat is passive; it just sits there as a storage form of body energy. "We feel that older people's reduced muscle mass is almost wholely responsible for the gradual reduction in their basal metabolic rate."

Vicious Cycle
Slowing metabolism sets up fat gain

Evans & Rosenberg explain that this reduction in muscle mass - and the slowing of metabolism that it causes - sets up a vicious cycle. As our muscle mass falls, our calorie needs fall with it. According to the authors of Biomarkers, most people need to take in about 100 calories per day less each decade to maintain a level body weight. The problem, of course, is that we continue eating the same. "Too many calories coupled with too little exertion, a reduced musculature, and a declining metabolic rate add up to more and more fat." This cycle, they conclude, will only worsen over time - unless broken by a program that increases muscle and restores lost metabolism.

Diet , of course, helps to control creeping obesity. You should avoid calorie-dense foods and emphasize foods high in fiber and bulk. Eat plenty of fruit, vegetables and whole grains. But the main solution for an "aging metabolism" is exercise. Exercise burn calories while you exercise, and after exercise you continue to use more calories than at rest. Even mild exercise leaves you burning extra calories an hour later. If you exercise harder and longer, after 12 hours your energy requirements will still be elevated. And even at rest, your metabolically active muscles still use energy. The more muscle you have, the more calories you use, round the clock. That's why weight training is so important. It builds and maintains the calorie-burning muscle tissue that makes - and keeps - you lean. Lifting weights keeps your metabolic fires burning strongly.

Don't Be Discouraged
Old muscle just as responsive

And don't let anyone tell you that you can't increase your muscle size and strength as you get older. Evans and Rosenberg and their colleagues at the U.S. Department of Agriculture's Human Nutrition Center on Aging at Tufts University have found that "the muscles of elderly people are just as responsive to weight training as those of younger people." Startlingly, an 8-week program of strength training by 87- to 96-year-old women confined to a nursing home resulted in a tripling of strength and a muscle-size increase of ten percent.

Their important conclusion: "Much of the loss of muscle as we age is preventable - and even reversible."

Dr. Lawrence Lamb agrees: "Developing an old muscle is just like developing a young muscle. You may need to be more careful and progress slower, but you can do it." Plus, keep training and pushing to your limit occasionally, and you'll keep your muscles - and your metabolism.

It comes down to this: Your metabolism won't slow down if you don't.

(For more information on Biomarkers see Recommended Books)

Copyright ©1997 Clarence and Carol Bass. All rights reserved.

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