(CNN) -- As we age we grow, not only in wisdom, (one hopes) but also in size (one hopes not!).
Staying active is important, especially as you get older, experts say.
Our body's response to aging seems to be a combination of muscle mass lost and too many calories found.
"As we are aging, we can expect to lose a little bit of muscle mass every decade," said Julie Schwartz, a dietitian at the Emory University School of Medicine.
"And when we lose muscle mass, that means our metabolism goes down."
And that slowing down means that if we don't change some lifestyle habits, we are going to pack on those pounds.
Just where those pounds land is determined by many factors.
The first, according to Schwartz, is whether you are a man or a woman.
"Most women will really gain weight in their hips and thighs," she said. "Men more around the mid-section of their abdomen. Then as women age and their hormones change, the tendency is to start depositing more in the mid-section as well as their hips. "
This basically means that losing hormones can transform us from a pear into an apple. But this reshaping, whatever the cause, is something to worry about.
A recent study by Harvard University and the National Institutes of Health found that women with larger waists, those measuring 35 inches or more, are at greater risk for cancer or heart disease than women with smaller waists.
For men, the key measurement for waist size is 40 inches. And if these numbers affect you, you're not alone. According to the researchers, in 2004, more than half of the U.S. population had an abdominal measurement that exceeded those limits. Yikes!
So what is an aging body to do?
Schwartz has one main mantra: "Stay active!"
While aerobic exercise is good for burning calories, Schwartz stresses the importance of not trying to lighten your workout load.
"Cardio is good, but strength training is important," she said. "With strength training you are constantly maintaining or maybe even adding a little bit of muscle weight. You are also putting a little bit of stress on your bones which helps aid and maintain bone density."
And dense bones are something women really need to strive for, given our propensity towards brittle bones, or osteoporosis, especially as we age.
On the other side of the how-to-age-gracefully-and-healthfully equation is the ever-important factor of diet and nutrition.
"As people age, we usually recommend decreasing calories slowly to help balance weight," Schwartz counsels. "But we also change the composition of what they eat as far as the protein carbs and fats go, based on their health goals."
She also recommends eating smaller meals more often and getting plenty of fluids to help boost that lagging metabolism. A simple, easy start is to eat off smaller plates, as portion size is important to successful dieting.
But mainly Schwartz wants us not to be too overwhelmed by all this slowing down and focus instead on taking small steps.
"Big steps are overwhelming, so just start small."
And the key to all of this slowing down stuff is to realize we can't stop the aging process, but we can start making sure we age the way we want to.
The optimal word here being: START.