Researchers at St Andrews University have found evidence that men prefer “normal” women despite the size zero trend, sending a clear message to girls who believe they have to be underweight to be desirable.

When shown photographs of 84 female students’ faces, male volunteers consistently rated those in the “normal” weight range as being the healthiest-looking and most attractive.

Women also tended to prefer the pictures of “normal” students, and the same results were found – perhaps unsurprisingly – when female volunteers rated images of men.

However, women who take the anti-slimming message too far by becoming overweight were also seen to be unhealthy and unappealing, the study showed.

Those who fall into the healthiest weight range – which includes actresses such as Scarlett Johansson, Kate Winslet and Jennifer Lopez – were considered more attractive than those who were thinner, such as Paris Hilton and Nicole Richie.

Lead researcher Vinet Coetzee said the results provided a solution to a problem that has puzzled scientists for a generation. She said: “We often remark on how healthy or unhealthy someone looks, but it can be very difficult to say precisely how we know this.

“Scientists have been trying to answer this question for decades, and have made many breakthroughs in our understanding of health and attractiveness, but until now they have tended to overlook the influence of weight.”

The study used arbitrary measures of “normal”, “underweight” and “overweight” based on ratings by those viewing the photos, but Ms Coetzee said by way of guidance that the World Health Organisation regards a Body Mass Index of between 18.5 and 25 as healthy. For a woman 5ft 5in tall, this would mean that anything under 112lbs (8st) would be underweight, and anything over 150lbs (10st 10lbs) would be overweight. Women heavier than 180lbs (12st 10lbs) would be medically obese.

Ms Coetzee and her colleagues at the university’s Perception Lab questioned students on their health, took their blood pressure and photographed their faces. Among the group, those rated overweight used antibiotics more frequently, had higher blood pressure and reported more frequent and longer lasting bouts of cold and flu than those of normal weight.

“Even at this young age, their health was already suffering because they were overweight and other people can spot this in their face,” Ms Coetzee said.

The researchers also identified a clear link between health and attractiveness, saying: “If you have a healthier partner it is not only long-term health that matters – you will have healthier children, but your partner’s health will also affect your own health in terms of the fact that they won’t infect you with diseases.”

Ms Coetzee’s PhD supervisor, Professor David Perrett, said her work could teach a valuable lesson to young women worried about weight issues.

He said: “This sends a strong message to all the girls out there who believe you have to be underweight to be attractive. The people making judgments in our study were all between the ages of 18 and 26 and they did not rate underweight girls most attractive. They preferred normal weight girls.”

While recent figures state that the average adult in the UK is classed as medically overweight, according to recent figures, significant problems have also been reported among teens and young women who make themselves too thin because they falsely perceive it as being attractive.

Criticism is often levelled at the fashion industry for fuelling this trend with size-zero models, but PR guru and Scottish Fashion Awards founder Tessa Hartmann said this was unfair. Though she described the use of dangerously thin models as “utterly ridiculous”, Ms Hartmann said: “We tend to insult a lot of women by constantly saying that these images are not good examples, but I think most women have the intellect to make that decision for themselves. We just need to look at the nation – the average size is a 16. That proves we’re not all being influenced.”

The research paper, “Facial adiposity: A cue to health?” by Vinet Coetzee, David I Perrett and Ian D Stephen, is published online by the journal Perception.

‘Aim for what’s attainable and healthy’

Attractiveness is related to health. We’re attracted to those who look healthy. But when it comes to rating our own attractiveness, or the weight or shape we should be, we’re not fantastic judges. Women tend to think they should be lighter than men think they should be.

Why is this? It’s because the people we are looking at as glamorous in magazines and on TV are often those who are underweight. Women often believe that is the ideal and that it’s attainable, when the truth is that for most women, it isn’t. We are therefore striving for something we can’t attain.

There’s a view that there’s a drive in women to strive for an appearance that’s not quite attainable, because if they’re striving for a very slim and petite figure, they might achieve normal weight. Will they then be left feeling guilty that they haven’t reached their ideal? Yes – researchers have termed it “normative discontent”. It’s statistically normal to be unhappy with the way you look.

There’s always been a great importance placed on the way women look, but this issue doesn’t just affect women. Men tend to think women like them to be more muscular than they actually do. Women tend to want men who are toned, but they don’t want Arnold Schwarzenegger.

It is important to be aware that this false ideal exists. Be aware that the way you think of yourself isn’t necessarily a reflection of what others may think of you. We also need to be more open about the use of airbrushing and more realistic about what is attainable. We need to aim for what’s attainable, healthy and sustainable.

Dr Gayle Brewer is a psychologist at the University of Central Lancashire, who specialises in the psychology of physical attractiveness and body image.