Analyzing every Playboy centerfold since the first one in 1953, they found the models' weight hadn't changed much over time, but busts and hips had diminished, while waists had become less tapered.
The study, published this week in the traditionally lighthearted Christmas edition of the British Medical Journal, does not offer much interpretation of the trend and experts warn against jumping to conclusions.
Does it mean the male idea of female attractiveness has changed over time - that men now prefer a less curvaceous woman, despite their protests that "heroin chic" is not sexy?
Or were the evolutionary scientists who theorized that curves symbolized fertility and that the most reproductively successful females were those who were able to store surplus energy in their curves wrong?
Or have humans now evolved beyond such primitive judgments as the ability to make it through famine?
Or is it simply that Playboy is now out of touch with what men find attractive?
"It's difficult to disentangle cause from effect," said the study's leader, Martin Voracek, a psychology researcher at the University of Vienna in Austria. "All I can say is that attractiveness is not that simple and is not constant over time."
"If Playboy didn't reflect ideals of attractiveness, they wouldn't still be around, so it must be that many men find this shape attractive," Voracek speculated.
However, Adrian Furnham, a professor of psychology at London University who has conducted research on judgments of female attractiveness, was not so ready to draw conclusions.
"I would have thought that to make any deductions would be highly dubious. Some years ago Playboy was the touchstone, but there are now dozens of these things around," he said. "You'd need a whole range of magazines from different countries which showed a consistent pattern. Then, I think, you could start worrying about an explanation, but until then it's just a bit of fun."
It's not as if the Playboy centerfolds are indistinguishable from bony catwalk models, Voracek said, "but at least over the last 15 years or so, there is some sort of converging trend."
Playboy spokesman Bill Farley acknowledged the curves on the centerfolds have changed.
"In the 1950s and into the '60s, the cultural norm was more of the hourglass figure - Marilyn Monroe, Jayne Mansfield. That was reflected in the pages of Playboy. As time has gone on and women have become more athletic, more in the business world and more inclined to put themselves through fitness regimes, their bodies have changed, and we reflect that as well," he said.
Many models these days tend to have thinner lower bodies.
"But I would think that no one with eyes to see would consider playmates to be androgynous," Farley said.
By Emma Ross