It is commonly believed that as we grow older, growing fatter is inevitable. The misconception is that our metabolism slows to such an extent that it's next to impossible to maintain an optimal weight. We can list "slow metabolism" along with "genes" and "glands" under Favorite Excuses for becoming heavier. My grandmother used to attribute her size 20 to "that gland trouble," when the only gland in question was salivary.

It's probably human nature to accept a sweeping explanation of a nagging problem, preferably one that we have no control over. However, according to Dr. Allen Green, director of the Bassett Research Center, while a change in metabolism does occur as we grow older, it is limited. We burn about 100 fewer calories a day for every decade we age. Though a consideration, it's relatively easy to compensate for 100 calories.

Metabolic rates, genetic heritage and misbehaving glands aside, the overwhelming reason for overweight is too many calories ingested and too few expended. It's our lifestyle that slows as we get older more than it is our metabolism. Except for recent history, before movement was engineered out of our daily lives, people and especially children, were much more active.

While visiting my hometown and my alma mater, The University of Missouri-Columbia, this week, I reconstructed a day in my life at age 20. UMC is an extensive site, roughly divided into halves, the Red Campus and the White Campus. I lived off campus and biked to school, with my backpack weighing in around twenty pounds. I had at least one class in some far-flung corner, like Art Appreciation oddly scheduled in the Industrial Engineering Building, on the outskirts of the Red Campus. Astronomy was required and held in the Physics Building, on the edge of the White Campus. Art was at 10:40, the Stars at 11:40, giving me a scant 10 minutes to traverse most of both campuses at a conditioning clip. An average day of going to classes, the library, the bookstore, Brewer Field House for racquetball and The Heidelberg, a revered student hangout, accounted for about three miles of walking. Biking and walking everyday carrying extra weight, plus Phys. Ed. - it's no wonder a body could tolerate Shakespeare's Pizza.

Then I graduated, got a job and a car, drove to work and sat in an office, and, over time, my body did as expected. Before The Walking Example Group, my activity level, like that of most American adults, was minimal and sporadic. Now, with consistent daily activity interwoven into my life, the creeping middle-aged weight gain has stopped and is starting to reverse. Though not at my college weight, I'm also not yet at my college activity level. It will take a while to make up for the last 20 years.

If metabolism drags a bit as we get older, so what? The limited influence it has on weight can be overcome through more motion and smarter food choices.

Brenda Berstler is founder of The Walking Example Group.