The changing shape of the model

By BBC News Online's Megan Lane

Fashions in clothing are cyclical, but when it comes to the ideal body, the trend is for an increasingly pared-down form.

In the 1950s, the curvaceous Marilyn Monroe epitomised the ideal woman. Today, casting agents would tell her to slim down and shape up.

Body of the decade

1950s: Marilyn Monroe 37-23-36

1960s: Twiggy 32-22-32

1970s: Jerry Hall 36-24-36

1980s: Cindy Crawford 34-24-35

1990s: Kate Moss 33-23-35

A report by the British Medical Association (BMA) published on Tuesday identifies a link between the images of "abnormally thin" models that dominate television and magazines, and the rise in conditions such as anorexia nervosa and bulimia.

The report says models and actresses have 10 to 15% body fat, compared to the healthy average of 22 to 26%.

In 1950, the average woman weighed about eight-and-a-half stone and had a 24-inch waist. Now, she is more than 10 stone, with a 32-inch waist.

Yet the women appearing on screen and in fashion spreads are much slimmer than they were 50 years ago, says Dr Vivienne Nathanson, the BMA head of science.

Brazilian model Gisele Bundchen: "Bag of bones"

"Marilyn Monroe's body mass index (body fat) was 20%, which is at the low end of normal, but people now think of her as hefty.

"In the past, there has always been some models or actresses who didn't fit the norm, but you rarely see that today."

And although thin is in, as in the 1960s when the waif-like Twiggy held sway on the fashion pages, that ideal has been updated to a slender frame with defined muscles and fulsome bosoms.

Think of Friends star Jennifer Aniston or Spice Girl Victoria Beckham, who admitted this month to being a stone-and-a-half underweight. Not only do these women stick to low-fat, high-protein diets, they indulge in rigorous daily workouts.

"There is not a certain size that makes people attractive, but [thinness] has become the norm. People haven't paused to consider if this is the right image or whether there are any alternatives," Dr Nathanson says.

Dying for food

60,000 Britons with eating disorders

10% are men

Disorders can be sparked by low self-esteem

"We have spent so long talking about the problems of being over-weight that not enough is known about the dangers of being underweight.

"By demanding this, we are damaging the health of these people, possibly permanently."

Liz Jones, the editor of Marie Claire and a former anorexic, described hugging Gisele Bundchen, the supposedly curvy supermodel of the moment: "She felt like a bag of bones."

Modern-day Adonis

Although men now account for 10% of the 60,000 people in the UK with an eating disorder, Dr Nathanson says those unhappy with how they look are more likely to over-train than under-eat.

Brad Pitt's films flaunt his fat-free frame

"But men don't have the role models that are so uniform as the women appearing in the media - there is more variety, and that in itself paints a more realistic picture."

Men can be susceptible to the six-pack tyranny. Today, rock-hard abdominals and perky pecs are de rigeur for a Hollywood leading man.

Witness last year's film Fight Club. Edward Norton, playing a wimp desperate to rediscover his masculinity, sported a body that would not have looked out of place in a Mr Puniverse competition, whereas co-star Brad Pitt's aspirational hard man had hardly an ounce of fat on his frame.

In the book The Adonis Complex, US psychiatrists Harrison Pope and Katharine Phillips and clinical psychologist Roberto Olivardia found that nearly half of men today did not like their overall appearance, in contrast to just one in six in 1972.

They argued men wanted to look like the mythical half-man, half-god because muscles are all they have over women.

Sean Connery as 007: No six-packs in the 1960s

"Women can now fly combat aircraft, run multinational companies and have eliminated every last male bastion," said Professor Pope, of Harvard University, when the book was released in April.

"Few women can bench-press 300lb, so the body remains the last refuge of masculinity."

Dr Nathanson says there is no one factor leading to an unhealthy preoccupation with body size and weight.

"We mustn't over-simplify it, but neither should we ignore that changes in society are frightening for many young people. They are not sure what roles and expectations are right for them.

"If you see young people anxious about fitting in, they tend to try to conform to a stereotype - they see an ideal that is accepted by society, and try to achieve that look themselves."