When the Beijing Olympics get under way this week Allie Outram will be glued to her television set at home in Bradford. An international athlete for 12 years, Outram once harboured realistic dreams of representing her country at the Games, but is now content with watching some of her contemporaries clock laps of the track. During her athletic career, she competed on the track, road and at cross-country for Great Britain alongside such athletes as Paula Radcliffe, once finishing as high as seventh in a world championship event.

But Outram's successes masked a dark secret. In a book Running On Empty, published this month, she reveals how an eating disorder and intense training regimens left her close to death. A sporty youngster, Outram began running when she was 14. “I represented my region in tennis and lacrosse,” she says. “But the solitary aspect of running appealed to me. I joined an athletics club and within three months of starting training was asked to represent England in some races.” In a bid to perform well, Outram began “carefully controlling” what she ate. “It started with me cutting out foods I considered ‘unacceptable', which was anything high calorie, but that soon became any carbohydrates or fats, then anything other than certain vegetables, salads or fruits,” she says. “In the meantime I began doing frantic exercise programmes, pushing my body to physical extremes, training twice a day or more.”

At her lowest point Outram's weight plummeted to 4st (29kg) and her body fat to 11 per cent. She spent two years as an inpatient in a hospital eating disorders unit. “I had bed sores and my knee bones rubbed together when I walked. My blood pressure was low and my heart rate slow. But I still wanted to run - and still didn't want to eat,” she says. “I starved myself until I was left with a black-and-white choice between eating or dying.” As she attempted to eat to recover, her anorexia developed into bulimia, which left her psychologically spent. “During a binge I wouldn't care what I ate,” she says. “I would consume other people's leftovers, and even found myself rummaging through dustbins to get my fix. I hated myself afterwards and would vomit and starve myself again.”

Yet her case was far from isolated. “At one World Cross Country Championship I can confidently say that, of six of us in the Great Britain junior women's team, four had some form of eating disorder,” she says. “It is so common in the sport, yet no coach or team manager ever expressed concern. I was never told that I was too thin, and was never withdrawn from a race because of my weight.”

In many ways she believes that the athletics environment helped to “legitimise” her eating disorder. “Outside of sport, people would think I ate too little and exercised too much, but within athletics my behaviour was not only accepted but endorsed and encouraged,” she says. “There were lots of others like me so it was easy to hide.”

By their nature, anorexia and bulimia are disorders that are shrouded in secrecy. But a study published last year in the Psychology of Sport and Exercise journal confirmed the true prevalence of the problem. Dr Angie Hulley, a sports psychologist who was then based at the University of Leeds, revealed that almost one in five of Britain's leading female distance runners has an eating disorder or has suffered in the past, compared with just 1 per cent of the general population. Some have reported a culture of shocking dietary practices, such as consuming paper to bulk stomach content and promote satiety without ingesting calories. “On international trips virtually all the girls had weird eating habits,” Outram says. “You would look around and see top runners eating just the inside of a bread roll for a meal, and it sort of confirmed that it was OK not to eat.”

What causes this plague-like spread of disordered eating? Dr Hulley, a former international marathon runner, says it is wrong to assume that sports such as distance running and gymnastics are directly to blame. You cannot catch anorexia from sport, she says, just as you can't develop the self-will to starve yourself by seeing skinny models in glossy magazines. “Eating disorders are not easy to explain as each case has a range of psychological factors unique to the sufferer,” says Hulley. “There is always going to be a higher number of sufferers in sports where thinness is normal because they provide an environment for vulnerable personal types to exacerbate and conceal their disordered behaviour.”

To some extent, a relatively low body weight is beneficial for elite athletes. Being overweight can limit performance in many sports because the body is forced to supply oxygen to fuel surplus fatty tissue. “Lose some weight and the oxygen goes directly to the working muscles instead, enabling faster and more efficient running,” Dr Hulley says. “But the danger is that some runners then get caught up in the mindset that they need to be even thinner to be a winner. There is actually a thin line between an optimum racing weight and one that is too low, and it is easy to overstep the mark.”

How do athletes keep training when their energy reserves are so depleted? “The body has a tremendous ability to cope with calorie deprivation for a while,” Dr Hulley says. “Eventually, though, it becomes too weak to sustain the activity, becomes prone to viruses and stress fractures and has to draw on all its reserves just to stay alive.”

Among those who have spoken openly about what is dubbed “anorexia athletica” are Charlotte Dale, a former European junior cross-country champion from Kent who weighed 4st at 16, and Bryony and Kathryn Frost. Now 24, the Frost twins were considered among Britain's best prospects for track medals at the 2012 Olympics, but last year revealed how they survived on just a few pieces of fruit a day because of anorexia. Even Liz McColgan said that in the run-up to the 1988 Seoul Olympics, where she finished second, her weight fell to 7st, which probably cost her the gold medal. “I was so weak and undernourished that I didn't have the energy to sprint for the line,” she said.

For those who do come forward, there are many more who conceal their condition. In 2003, Helen Lee, a former Middlesex county and South of England cross-country champion died at the age of 18 from pneumonia and organ failure thought to be a direct result of her long-term battle with anorexia nervosa.

Dr Sheelagh Rodgers, a clinical psychologist who is a consultant to the English Institute of Sport and a member of the UK Athletics Working Party on Eating Disorders - an expert panel set up with beat, the eating disorders charity - says there is still much ignorance among coaches about eating disorders. She has encountered many horror stories in her dealings with athletes over the past ten years. One male coach would conduct a weekly weigh-in for his female athletes and instruct the heaviest to wear a pig mask for the duration of a track session. “There are female athletes whose coaches call them ‘Tank Thighs' or ‘Lardy Legs' or make repeated remarks about the size of their arses,” Dr Rodgers says. “For someone who has underlying insecurities, such comments can be a trigger for them to start cutting down on food.”

Although now recovered, Outram's years of self-starvation have caused permanent side-effect. Now 31, she menstruated for the first time only recently. Amenorrhea - the absence of periods - is common among anorexics, whose bodies contain insufficient fat to support a growing foetus. Her skeleton is weakened by osteopenia (a precursor to the brittle-bone disease osteoporosis, which usually affects post-menopausal women) and, as a consequence, she has been taking the contraceptive Pill, to provide bone-protective oestrogen, for the past ten years. She is to marry in December and would love to have children but is concerned about the long-term effects that undereating and overexercising may have had on her fertility.

Still, Outram says, she has reached the point where she can run for enjoyment and can stop for weeks on end without feeling guilty. “It's been a long struggle, but my Christian faith and my fiancé, Lewis, have really helped me,” she says. “I will enjoy watching the triumphs at the Olympics, but part of me will be deeply saddened by the sight of athletes who are there, even winning medals, at the expense of their health. It's not worth it.”

Running on Empty by Allie Outram is available from walkingfree.org (£7.95 plus p&p). If you are an athlete with an eating disorder, contact the beat charity at help@b-eat.co.uk, or telephone 0845 634 1414.

Peta Bee is the winner of the Medical Journalists' Association Freelance Journalist of the Year award.

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club