Joan Smith: It's enough to make a grown woman turn to food and drink

The message is that women should aspire to be nothing

What does a normal woman look like? Not like Lily Cole, the skinny 17-year-old model who has the thinnest legs I've seen on anyone who isn't actually a horse. Nor like Erin O'Connor, whose gaunt features stare out of the fashion pages in what looks to me like a mute plea for someone to give her a square meal. Hasn't anyone noticed, up in the rarefied atmosphere of high fashion, that most women don't look anything like Cole, O'Connor or Kate Moss? Ah, says the fashion industry, but that's how most women would like to look - if only they weren't overweight and perpetually on diets, that is.

The contrast is so stark - wraith-like models on the one hand, rising numbers of obese women on the other - that it sometimes seems like a conspiracy, expressly designed to keep the vast majority of women in a state of discontent and self-loathing. It certainly seems to be the case that catwalk models are getting thinner as ordinary women get fatter, which means that the cultural ideal of beauty is more out of reach than ever. While high-street stores say the average woman now wears size 14, the latest fad on the catwalk is for size-zero models, which seems to me to contain a subliminal message that women should aspire to be nothing.

How sick is that? The whole business would be laughable if the consequences weren't so dire: last month a model died from heart failure at a fashion show in Uruguay after three months of ferocious dieting. Luisel Ramos, 22, had apparently been told by a model agency that she could "make it big" as a model if she did precisely the opposite and lost lots of weight; when she stepped on to the catwalk in Montevideo, her new look prompted applause from spectators who are no longer able, I assume, to tell the difference between a woman who is fashionably slender and one who is starving to death. Ramos is an extreme case but it isn't surprising that there are now calls for an extension of the ban on excessively thin models - defined as a body mass index of 18 or below - which started in Madrid.

London Fashion Week, which opens tomorrow, has resisted the call and experts on eating disorders say that legislation may be necessary to protect models and the young women who aspire to be like them. About time, too; fashion is an industry and there's no reason why it should be exempt from the normal requirement to provide safe working conditions. What could be more enjoyable than a confrontation between the prima donnas of the fashion world and the down-to-earth men and women who enforce health and safety laws? I bet they'd have something to say about those infamous platform shoes that landed Naomi Campbell in a heap on the catwalk a few years ago.

It may be that the cult of extreme skinniness is aesthetic, in the sense that clothes are more important to the fashion industry than the people who wear them; models are expected to adapt to the garments they have to wear, even if that means risking their health, rather than the other way round. But I can't look at super-skinny women without seeing evidence of a denial of femininity, a fear of voluptuousness, which has something to do with not wanting to recognise female power.

As women are achieving more in terms of status and success at work, models are fading away on the catwalk, and I don't think it's a coincidence. When normal weight is pathologised in this way, and freakish weight-loss rewarded, we shouldn't be surprised if millions of ordinary women are confused - and overeat.