Study Investigates What Women Really Want

Guys—size matters, but not in the way you think. Women are drawn to men with low body fat—not macho features, such as a manly jaw or six-pack abs, according to a surprising new study published in Proceedings of the Royal Society B: Biological Sciences. Overall, the guys women rated as most attractive had about 12 percent body fat.

Intriguingly, the scientists also found that men’s antibodies, not hard bodies toned by long hours at the gym, are what turn fertile women on. From the evolutionary point of view, that makes sense, since a woman would choose a mate with optimal genes and a healthy immune system to father her kids.

But how can women tell at glance which men have these desirable traits? Here’s a closer look at the research.

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Scientists used to think that a macho appearance would be an evolutionary asset for men, based on the “immunocompetence handicap hypothesis.” This theory holds that a highly masculine appearance indicates that a man have overcome the “handicap” of contending with the negative effects of having high levels of the male hormone (which makes men more susceptible to infections).

Therefore, proponents of this theory believed that a manly appearance should be highly alluring to women, as an indication of “good genes.” In other words, a man needs to be very fit and healthy to overcome the so-called testosterone “handicap.”

Yet studies show that women don’t consistently prefer the most masculine-looking men, nor are macho looks always linked to better health in men across studies. Body weight, however, is strongly associated with both a robust immune system and good health, with both very overweight and very underweight men at greater risk for medical problems.

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Investigating the Secret of Men’s Sex Appeal

To find out what makes a man most likely to be a babe magnet, the researchers recruited 69 young white men of varying appearances and weights. All of the men were photographed in what the researchers call “standardized underwear” and their body fat percentage was measured.

Almost two-thirds of the men were of a normal weight, four percent were underweight, and the rest were overweight or obese. The men also underwent blood tests to check their levels of circulating testosterone and antibody levels before and one month after getting a hepatitis B vaccination.

Twenty-nine young heterosexual women who were in the fertile phase of their menstrual cycle (and not taking birth control pills) were asked to rate the sexual attractiveness of each man’s face and body. The photos were also rated by a separate panel of 20 heterosexual women on the men’s degree of masculinity of the man’s appearance. A third group of women evaluated how fat or thin the men’s faces were.

The ratings were then compared with the men’s testosterone and hepatitis B antibody levels one month after the vaccine to identify men with the healthiest immune system response.

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What Really Makes a "Babe Magnet"

Contrary to what the immunocompetence theory would have predicted, the researchers found no correlation between a man’s masculinity rating and how sexy women found him. Nor did the macho-looking men have a stronger immune system response to the hepatitis B vaccine. And their levels of testosterone weren’t any higher than those of men with a less manly appearance.

Instead, the women swooned over guys with low body fat, with men who had 12 percent body fat being deemed the most attractive. Slimmer men also had a more robust immune system. There was a link between weight and testosterone, with higher levels found in thinner men.

“We found that a man’s weight serves as a better indicator of the relationship between immune response and attractiveness than masculinity does,” University of Pretoria researcher Vinet Coetzee told LiveScience.com. Coetzee theorizes that women use weight, rather than macho features, to subconsciously make hot-or-not judgments about the men they meet.

This research, Coetzee added, "serves as a stepping stone for future studies that could test this relationship in different populations using alternative measures of immunity."

The researchers also created two intriguing composite photos, one with the combined features of of the eight men with the weakest immune systems and another with the combined features of the eight with the healthiest. Which guy do you think is hottest?

Chubby man and thin man

Above: Composite images of men with low and high immunity. On the left is a composite image of the eight men with the lowest antibody response in the study. On the right is a composite image of the eight men with the highest antibody response in the study.

Photo courtesy of Vinet Coetzee.

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