It's that time of year again, when men replay the Victoria's Secret Fashion Show or thumb through the Sports Illustrated swimsuit issue while their women sit nearby feeling lousy about the inevitable weight gain that goes with the coming winter months. These models have set the new standard for sexiness: large, pert (and often surgically enhanced) breasts, a microscopic waist and perfectly sculpted, cellulite-free hips and thighs.

Thanks to pop culture icons, women think that having a body like 54-kilogram Heidi Klum's is the answer to a sizzling and sexy relationship. When Reader's Digest asked women when they feel sexiest, they said it was when they weighed less than they do now. In fact, 80% said that losing weight would improve their sex life (among women who consider themselves obese, it jumps to 95%). Men showed insecurities, too. A whopping 70% think a slimmer waistline would lead to better sex, and 42% said they would go shirtless only in front of their partner.

But here's the big disconnect: despite idealised images, guys really don't expect (or even want) their wives or girlfriends to be supermodel thin. And women aren't looking for Brad Pitt in their beds. Yes, overweight people are having good sex. They know what researchers and scientists are beginning to uncover: a great sexual experience comes mostly from our minds, not from perfectly proportioned bodies. In fact, striving to look like a lingerie model may be a sexual turnoff. The average body mass index (BMI) of those models is an unhealthy and underweight 17. Women with a BMI of 18,5 are less likely to conceive, and they suffer a drop in hormones that contribute to libido. So that smouldering stork-like model may look phenomenal on the pages of fashion magazines – but may not be a firecracker in bed.

Extra kilos can be sexy
Overweight adults are not only having lots of sex, they're also getting extreme enjoyment out of it, says Dr Martin Binks, director of behavioural health at the Diet & Fitness Center at Duke University. Binks's study subjects are trying to drop kilograms and probably should for health reasons. But what's remarkable is that the biggest improvement in their sex lives came when they lost just 10% of their body weight. "That's a very minimal weight loss, and these people were still substantially overweight," he says.

Still, after a year of dieting, participants who had felt sexually unattractive went from 68% to 26%. All this goes to show that sex is more about attitude than weight, says Binks.

In addition to having a more positive body image, people who've lost weight have more energy and feel more comfortable communicating with a partner about sexual techniques, fantasies and feelings.

What's more, having meaningful, not recreational, sex induces the release of the hormone oxytocin. "It makes a person feel love and empathy," says noted heart surgeon Dr Mehmet Oz, co-author of the YOU series of health books. "Meaningful sex can also lower blood pressure, and it tells the gut not to send signals to the brain to eat." Bottom line: a healthy sex drive can lead to weight loss.

There's an emotional link, too: "It makes sense that women who are feeling very full are less interested in sex," says Sonya Satinsky, project coordinator for the Center for Sexual Health Promotion at Indiana University. One possible explanation, she says, goes back to having bad feelings about their body, leading to a lack of desire.

Men worry too
Women aren't the only ones who are misguided about weight and sex. "Men are increasingly dissatisfied with their bodies," says Dr Viren Swami, of the University of Westminster in England, who has extensively studied the science of attraction. "Some want to be thinner, but most want to be more muscular, and they are increasingly attempting to bulk up."

By some accounts, the rate of steroid use among adolescent boys is now comparable to the rate of anorexia and bulimia among adolescent girls. No wonder, since boys are being targeted with images of hairless, V-shaped Adonises in fitness magazines and on-screen.

Laws of attraction
Throughout history, having a fit and healthy body helped humans find a mate and reproduce successfully. Centuries ago, certain female traits (youth, a small waist, big breasts) indicated fertility. In turn, certain male traits (broad shoulders, dominance, good provider) indicated his ability to protect and care for mother and child. Evolutionary psychologist Dr Devendra Singh, of the University of Texas, says men are actually not concerned about a woman's weight: they're attracted first and foremost to an hourglass shape, which in most cases means a waist that is 70% as wide as a woman's hips, regardless of dress size, a proportion that's a sign of high fertility.

But Swami's research suggests different cultures have different standards. Men in Western countries like Britain and the US flock to thinner women (with a BMI of around 21). Guys in Mediterranean countries like Spain and Portugal, which are less affluent and still developing in many ways, consider larger women with curves extremely desirable. This may explain why Latin American men go gaga over divas with well-endowed bottoms, like Jennifer Lopez. "In most traditional societies, people who are able to put on body fat are rich and can afford to buy food," Swami says. Men whose ancestors hail from regions where food was scarce year-round or seasonal (like parts of Africa) find heavier women very fertile and therefore sexy, says Dr Robert Friar, a professor of biology at Ferris State University.

When given a choice, women prefer men with broad shoulders and a thin waist, according to a 2006 study by researcher Margaret Braun of Portland State University. But physique is not all that crucial. "When women are looking for someone to settle down with, they start focusing on other important things," says evolutionary psychologist Dr Jason Weeden, of Arizona State University. "Is he going to be a good provider? Is he a reliable guy? Does he want the same things she does?"

For both sexes, the real key to attraction may lie due north. The face is a stronger predictor of sexiness than the body. In a recent study, 24 people ages 18 to 25 rated digital photos of faces and clothed bodies to determine which one figured more strongly into overall attractiveness. Women thought a man's face accounted for nearly half of his overall attractiveness. For men, the face was an even stronger predictor of sexiness. The theory, according to study author Marianne Peters of the University of Western Australia: the face reveals intelligence, personality and confidence levels – all things that increase the odds of a great sexual relationship much more than a smaller pants size.

Personality counts
"If Queen Latifah doesn't think she's sexy, she sure does a good job of fooling us," says Dr Pepper Schwartz, a sociology professor at the University of Washington in Seattle. "She carries herself like she's a babe. And a lot of men think she is."

Once we get to know a person, the non-physical aspects become much more important in long-term relationships and pleasurable sex, says Swami. Still, this is one area of study in which scientists may never have absolute understanding. "Even after all the studies I've done," he says, "I still find myself thinking about what attracts me to someone else, and I don't really have an answer. We've always assumed there's one type of person that we always go for, but that isn't the case. We see a myriad of people in our everyday lives, and we're attracted to different people at different times for different reasons. There is a part of attraction that should remain shrouded in mystery."

After all, a bit of mystery can make sex a lot more fun.

Additional reporting by Kathryn M. Tyranski