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). Researchers led by Dr. Ancel
Keys at the
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). 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 wholly 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
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.