Doctors now believe crash dieting is the best way to beat obesity. But does it work – and is it safe? After the deaths of two dieters, Jane Feinmann investigates

Crash dieting, otherwise known as living on starvation rations, is back in the news – but with a twist this time. Coroners reported last week on the deaths of two women who were on a severely-restricted calorie intake diet to lose weight fast. Yet despite these fatalities, doctors and obesity experts are queuing up to reassure the public about the safety of the modern equivalent of eating cabbage soup for a week to get into that little black dress.

This sudden enthusiasm reflects the extent of the UK's recent wake-up call to the dangers of obesity. One in four of the population is now clinically obese (having a BMI of 30 or more with a waist measurement of more than 94cm for men and 80cm for women) putting them at significantly greater risk of heart disease, some cancers, arthritis and diabetes.

Instead of constant harping on about the dangers of excessive weight loss, a landmark report from the National Institute for Health Clinical Excellence in July 2008 made it clear that our capacity to deny the flab in the mirror poses a far greater health risk. Once we're over a certain weight, we're no longer being urged to lose weight slowly but surely. Fat people are more motivated to stay on track the more sensational the speed with which they drop dress sizes. But is it really a good idea to crash diet?

At 17st 7lb, Samantha Clowe, 34, had a BMI of 37 when she went started a very low calorie diet (VLCD) because she "didn't want to be a fat bride". She died of heart failure in Leeds last year after shedding 3st, 11 weeks into a diet that allowed a daily intake of just 530 calories in soups and shakes – a quarter of the recommended daily calorie intake for a woman.

Her brother Daniel claimed there was "too much pressure on women to be like skinny celebs", while the coroner cautiously implied in his report last week that her death "may be related to her low-calorie diet and weight loss". But doctors disagreed. "Samantha's death tragically shows the real dangers of being obese," commented Dr David Haslam, chair of the National Obesity Forum. "The truth is the number of sudden deaths among the obese ... is significantly higher than those that occur among people on VLCDs," said Professor Iain Broom, director of the Centre for Obesity Research at Robert Gordon University, Aberdeen.

The following day, the Derby Coroner's Court reported on the death of Susan Alderson, 49, a diabetic with liver problems, who used another way to lose weight fast: gastric banding. This involves having a silicone loop tightened three-quarters of the way up the stomach so people feel full after eating relatively little. At 16st, Susan had a BMI of 44 and had been advised to have the operation for health reasons at Derby City General Hospital in January, but died of internal bleeding hours after surgery.

Once again, the tragedy seems unlikely to halt the meteoric rise in the popularity of the procedure, not least since the TV presenter Fern Britton admitted that it was a gastric band that had shifted 5st in 2006. The private sector, which has invested heavily in obesity surgery, can also rightly claim to have made this operation safe: while one in 200 gastric band operations in the NHS are still thought to be fatal, some private sector providers insist they have a zero mortality rate as a result of extensive pre- and post-surgical care.

What really counts, however, is the level of support in changing the way people feel about themselves and the food they eat. The benefit of a crash diet, it seems, is that enforcing a reduced appetite gives a breathing space to people who have obsessed about food for years. With sufficient daily nutrients to keep them healthy, the key to successful and sustained weight loss is the extent to which they use this transition period to develop a healthy diet and a balanced lifestyle, getting used to being thin and active again. Without such changes, the weight will pile back on.

Providing this support is not necessarily straightforward. "People who maintain a clinically obese body weight have a habit of consuming body-builder levels of calories and of course that has to change," says registered dietitian, Cirian-Marie Beddoes, head of Weight Management Services at The Hospital Group.

"Severe calorie restriction carries risks, particularly if the few calories consumed are low-quality," explains Beddoes. "You can consume 1,000 high-quality calories and blossom or the same number of calories in junk food and you'll be ill." Her team of dietitians provides two years of one-to-one aftercare, with food diaries and telephone consultations to check for symptoms of malnutrition: hair loss, brittle nails, skin pallor, apathy, moodiness or aggression.

The dietitians see it as a priority to provide psychological support, including neuro-linguistic programming and cognitive behavioural therapy. "These people often feel crap about themselves. Our job is to nurture and nourish their love of food, a healthy balanced diet and being socially and physically active," Beddoes says. "Changing lives requires intensive and skilled intervention."

Most VLCD companies such as Cambridge Diet provide little support. LighterLife leaves pre-diet preparation to the GP but does provide group counselling post-surgery, run by graduates of a training programme lasting just four weeks. "Before and after" success stories in ads may hide less-impressive long-term success rates.

NHS obesity treatment is largely restricted to occasional surgery, with increasing use of prescription drugs: Reductil tricks the brain into believing the stomach is full, while Xenical, which has its own support phone line, blocks the absorption of fat, causing unpleasant side effects for anyone taking the drug while eating lots of fat. "The failure of the NHS to invest in obesity services, having put all the funds into anti-smoking, makes my blood boil," says Beddoes, who moved to the private sector last year.

There are signs of changes. The Department of Health launched its Healthy Weight, Healthy Lives campaign last year. And in Scotland, the Counterweight Programme is a dietician-led service. If you're thinking of attempting rapid weight loss, consult your GP first. It could be some time, however, before we can rely on the NHS to get us into that little black dress.