Catherine and Carolyn Smith were 58 years old when these photos were taken. Catherine, left, weighed 70 pounds more than her sister, Carolyn. Judges thought Catherine looked five years younger than her twin.

Women of a certain age have always suspected that every pound lost from their hips adds a wrinkle to their face.

Turns out they were right.

And now they have research -- from Cleveland-area plastic surgeon Dr. Bahman Guyuron -- to back them up.

Guyuron, the chief of plastic surgery at University Hospitals Case Medical Center, will report his findings in the April issue of Plastic and Reconstructive Surgery, the journal of the American Society of Plastic Surgeons.

He, along with six residents and fellows, studied 149 sets of identical twins, all women, who attended the Twins Days festival in Twinsburg in 2006 and 2007.

The research began with each twin completing a five-page questionnaire about her life, including how much time she spent in the sun, how much she smoked and whether she used alcohol or took certain medications.

Beverly and Barbara Price were 69 years old when these photos were taken. Beverly, left, spent less than eight hours a week in the sun. Her twin sister, Barbara, soaked up the rays for 17 to 25 hours a week. Judges thought Barbara, right, looked about four years older than Beverly.

Then four judges -- plastic-surgery and research fellows who weren't involved in the research -- viewed photos of each twin and estimated how much older one looked than the other. The judges had no idea how the twins answered the questionnaire.

Here's what that research revealed:

If the twins were 40 or younger, the heavier one looked older. After the age of 40, the twin who gained a little weight looked younger. And after 55? She needed to gain even more weight to appear youthful. How much more, of course, depended on the woman's height.

"At age 55, if you gain a little bit, it's not going to help," Guyuron explained. "You have to gain a little bit more -- almost twice as much as you would gain at age 40 -- to see the effects."

The doctor is not suggesting women gain weight, which can cause health problems, just reporting his findings.

And it's not just waist size that affects a woman's looks.

The researchers also found that:

• For every 10 years a twin smoked, she appeared two years older.

• The twin who used hormone-replacement therapy appeared younger, but only if she took it for at least 16 years. At the age of 60, she appeared two years younger. At the age of 70, four years younger.

• The twin who avoided alcohol looked significantly younger.

• The divorced twin looked 1.7 years older than her married sister. But the widowed twin looked two years younger.

• The more time a twin spent in the sun, in outdoor activity and without sunscreen, the older she looked.

• Current or past use of anti-depressants made a twin look significantly older.

"I'm hoping, No. 1, that this is going to put science behind some of the things we do," said Guyuron, who, along with other plastic surgeons, uses fat injections and fillers to help patients appear more youthful.

"But the more important aspect to this research," he says, "is to see if we can help the public adjust what they do -- their social behavior and lifestyle -- to keep themselves younger.

"They have an opportunity to make some alteration to their behavior before it's too late."

So we can save face.

But it could cost us our fannies.