The National Institute for Clinical Excellence (Nice) issued guidelines last week to help improve the care of people suffering from eating disorders. They estimate that one in 20 women will suffer some symptoms of eating disorder, with one in 100 requiring medical treatment. Particular emphasis has been given to the specialist care, rights and treatment of adolescent girls who make up 50 per cent of eating disorder cases.

Raising awareness of the signs, symptoms and causes of eating disorders in young girls will help schools, doctors and families to both understand and intervene earlier in the disorder. But that leaves another 50 per cent of older women and men with the same problems but without the attention. Public perception already pictures eating disorders as a young girl's problem - which it is, but not exclusively.

Eating disorders can strike vulnerable people at key 'crisis' moments throughout their whole lives. Photographer Clare Park is an ex-dancer and model, who has worked extensively with anorexics and who was once anorexic herself. She says many anorexics share certain personality traits: 'In my experience, people blocked into the anorexic pattern of thinking are people who struggle with quite intellectual thought processes but are unable to fit them into their real life and family scenario, so they struggle with individual concepts outside their immediate control. They are often free thinkers, very individual, but also very driven and self-disciplined and with an ability to throw themselves into something. You can recover from an eating disorder, but you can't recover from the personality that helped cause the eating disorder. That vulnerability will always be there, but can be rechanneled.'

Our sense of body image may intensify as different points in our lives. Older women sometimes develop a disorder called 'anorexia tardive' after menopause, which is believed to be caused by a form of depression, and which can be difficult to diagnose and treat as it can be obscured by common digestive problems and body changes that are a natural feature of ageing.

Another vulnerable group are women who develop a disorder after the birth of a child, where it is frequently a symptom of postnatal depression. Deanne Jade, principle of the National Centre for Eating Disorders, believes that this is the kind of 'relapse' disorder that Princess Diana suffered from.

Men who suffer from eating disorders suffer the additional stigma of manifesting an 'unmanly' illness that is publicly perceived as a problem for teenage girls. The good work done by the Nice guidelines, which help keep awareness of eating disorders in the public eye, may be lost on these vulnerable groups, who are almost invisible in the medical studies or public consciousness.

According to Deanne Jade, this is because most adult sufferers will also have been adolescent sufferers. 'Many of the adult cases are relapses. True adult-onset anorexia is rare, so focusing on younger people will help older people too.' But older sufferers are low-priority and harder to diagnose. 'A young girl with a problem has people in control of her life: teachers, parents, doctors. Older people are autonomous. They can hide their disorder better.'

The anorexics' tricks and rituals to avoid food are notorious: specialists describe girls who put ball bearings in their hair scrunchies so they can fake their weight when they are weighed in their underwear; or who drink litres and litres of water before being weighed; who will sleep in a freezing cold room with the window open and no duvet, because they know that being cold burns more calories; or who will only consume food in precisely measured portions. Clare Park would drink cups of tea to fill herself up when she suffered from an eating disorder: 'But I'd never let my mother make me tea, in case she put too much milk in.' She trained with dancers who would allow themselves 'one fingernail of cottage cheese'.

It's grisly to talk about an eating disorder as 'glamorous', but all those pale, intense young girls slowly starving themselves exerts a fascination that a depressed, post-menopausal woman can't compete with, and which these guidelines, like all awareness campaigns, do nothing to address. The Nice guidelines make clear recommendations for the best treatments we currently have. But while they are an impeccable distillation of the combined expertise and recommendations of specialists, that's mainly all they are: the opinions and experiences of a small group of specialists. Randomised control trials, the gold standard for measuring the efficacy of clinical treatments, have not been used anywhere in the guidelines, and clinical trials have been used in only a few of the dozens of recommendations.

For the first time there is now a standard set of treatments and procedures for all health professionals and carers to follow, with an information booklet for patients and their families, so gold-standard treatment can be standardised across the UK. Anorexia and eating disorders are highly complex problems that also affect the families of sufferers profoundly, so a combined approach to treatment is recommended that involves patients, their families and professionals. Deanne Jade welcomes the guidelines, but with reservations. 'There just aren't enough resources to deliver them to everyone who needs them. And although they represent some excellent specialist experience and best practice, the truth is that we still have very little solid evidence to base any treatment guidelines on.'

The guidelines recommend a range of psychotherapy, psychodynamic therapy, cognitive behaviour therapy and family therapy for anorexics. 'One hospital will favour one kind of treatment and use it a lot, but who knows if another kind would be better? Or, if it works, which component of it worked? How do you know if your patient would have got better without treatment?'

In the absence of proper trials, treatments for eating disorders have, to a large extent, been driven by the personality, interests and preferences of the specialist in charge, and many remain controversial. (A recent review by the Royal College of Psychiatrists found that specialist services provided in the NHS were about 50 per cent of what is needed.) According to Deanne Jade, the treatment of an anorexic will be informed by one of five models of anorexia. The first sees anorexia as a symptom of someone with delayed emotional development. When the girl hits puberty, she is afraid of having to grow up, and terrified by her changing body. She starves herself to remain a child. Her treatment will be feeding to produce the physical changes of maturity, followed by psychotherapy to come to terms with adulthood and sexuality.

The second model sees anorexia as an identity problem. The patient sees herself as lacking any real sense of self, she feels 'invisible', as if she isn't real. She can't become an autonomous person because there's no 'person' there. In this case, there is little emphasis on feeding, unless her condition is dangerous, and lots on therapy to build the sense of self she didn't establish early on.

On a visit to an eating disorder ward a short while ago, I noticed how powerful these 'lost girl' anorexics are. One nurse told me that some carers work obsessively, cancelling holidays and neglecting their own private lives because they want to be the one to 'save' their patients. 'You have to be very careful not to be too manipulated by them. The girl who wants to stay a child can be incredibly appealing and moving. You want to help her and look after her, and be the one who doesn't let her down.'

The third model is the feminist cultural model, which sees women as victims of conflicting demands to be both feminine (soft, small) and strong (successful, sexy). Women retreat into eating disorders as an escape route, and to gain control of a situation. Therapy for this model will be informed by feminist theory and beliefs.

The fourth model sees the problem as an obsessive fear about fatness, with associated anxiety disorders centred on food and distorted body image. In this case, treatment will be to reduce anxiety and encourage a realistic and healthy body image.

The fifth model applies to male anorexics. There are several theories about the roots of this disorder, but a common one is to see the problem as rooted in sexual identity. The boy may want to starve away his body fat, which represents his 'feminine' side'. The writer Franz Kafka was anorexic, and his biographers have noted his fear of sexuality and his avoidance of meat and alcohol in order to retain a sense of physical 'purity'.

'Of course, there are commonalities and crossovers in all the models,' notes Deanne Jade, 'and they make sense, but we can't prove that any of them are right, or more right than any other.' Clare Park points out that eating disorders have existed since medieval times: 'Then they were imbued with mystic or religious significance. In the Victorian era they were considered a symptom of hysteria.' Our theories may be as much a feature of our time as those were, and may one day come to look as ridiculous.

'We do need a more rigorous approach,' admits Deanne Jade, who was consulted about the Nice guidelines, 'but this is a great step in the right direction. We've been invited to submit ideas for trials, and should have the results of the first proper tests in 2012. That's when we'll be able to issue really good guidelines.'

The new guidelines recommend outpatient treatment as a first choice, with inpatient treatment only for those at serious physical risk. 'But I ask myself if an eating disorder unit is the best place for an impressionable young girl to be,' says Deanne Jade. 'As any inpatient will tell you, a specialist unit is the best place to learn how to be really, really good at anorexia.' They also breed their own subculture. 'Some patients have reported bullying and intimidation by the hard-core cases. If they eat anything at all, they're called fat cows.'

Deanne Jade would like to see a school programme: 'Not talking to girls about the perils of anorexia and bulimia, which just glamourises it and gives them ideas. I like to talk to them about their experience as girls in today's world. I ask rhetorical questions like, "Who is pulling your strings?" It's about the subtle, hidden causes of the disorder, about pressures, and expectations and individuality versus peer pressure, and body image - not about eating.'

Clare Park wants to use her photography to help anorexics identify their feelings. She feels passionately about the way women feel disenfranchised from their bodies (it's her self-portrait on the cover of Naomi Wolf's The Beauty Myth). Over the last 15 years she has produced a series of self-portraits entitled 'Contradictions of Anorexia and Motherhood'.

She uses many different symbols to capture the essence of these 'disorders'. 'I showed my son a range of my photographs and asked him to pick one that he thought was about being unhappy or upset. He chose a picture of a woman bent over with her head in her hands and said, "When I'm upset I get a fizzing in my head so I want to hold my head and curl over." The picture allowed him to crystallise that thought and to express it, which would have been hard to do in a verbal way. Anorexia is an expression of overwhelming thoughts and emotions that can't be contained or expressed in any other way. We need to help people to find other way of expressing themselves.'

· National Centre For Eating Disorders: 54 New Road, Esher, Surrey KT10 9NU. For more information, call 01372 469493