There's an old saying that, as you get older, you need to choose between your face and your rear end. In other words, if you're skinny you'll look good from behind, but your face will suffer.

Depressing as it may seem, there is some truth to the saying. A couple of studies have found that women with a low body mass index (BMI) have increased skin aging -- including one study of identical twins. When the twins were under age 40, the heavier twin looked older. But after age 40, it was the thinner twin who looked older [source: Guyuron].

Do skinny women just look older, or do they actually have more wrinkles? Actually, both are true. "In general what happens is, as your BMI goes lower you lose some volume of soft tissue, particularly over the age of 40," explains Robert Weiss, MD, Dermatologist at the Maryland Laser Skin and Vein Institute, Associate Professor of Dermatology at Johns Hopkins University, and Fellow with the American Academy of Dermatology. "When you lose that volume of soft tissue, the wrinkles do either become deeper or more noticeable."

It doesn't help that skinny women may be more likely than those who are heavier to indulge in the behaviors most notorious for spawning wrinkles. For example, thinner women might be more likely to slip on a bikini and go sunbathing. Or to keep their slim physique, they might smoke cigarettes or yo-yo diet.

So if thinner women have more wrinkles, is the opposite also true? Yes, heavier women may look less lined as they age because they have more fat padding just beneath the skin (subcutaneous fat). They also might have a little extra collagen (the protein that gives skin its elasticity), says Dr. Weiss. However, don't think that wrinkle prevention is any justification for gorging yourself on Whoppers and pints of Ben & Jerry's. Being overweight can lead to a number of health problems that aren't worth the reduction in wrinkles.

You don't have to be zaftig to avoid wrinkles. You just need to take good care of your skin. Read on to learn the best ways of avoiding prematurely aged skin.