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For decades, we've been told that when it comes to losing weight, slow and steady is the way to go, the Daily Mail reports.

'Rapid weight loss is unlikely to help you maintain a healthy weight long-term,' says the NHS website.

'And it comes with health risks.'

Losing weight any faster than 2lb a week has been linked to problems such as gallstones (because it upsets the balance of cholesterol in the body), malnutrition and fatigue due to the sudden drop in calories.

There is also the widely held view that crash dieters will put the weight back on more quickly because drastic food plans can't be sustained long term.

But research is turning this advice on its head. Last month, an Australian study in the Lancet showed rapid weight loss was more effective in the short term than a gradual, sustained approach.

One group of obese adults were put on a 12-week rapid weight loss programme with meal replacements of 450 to 800 calories a day (an average man needs 2,500 calories a day to maintain his weight. For a woman, it's 2,000 calories).

Another group was put on a gradual weight loss programme, cutting 500 calories per day.

More of those in the rapid weight loss group achieved the goal of losing 15 per cent of their weight.

When the researchers followed up the participants two years later, both groups had regained most of the weight they had lost. But there was no difference in how quickly they put it back on, which flies in the face of conventional thinking that losing weight too quickly means you'll put it back on just as fast.

'The idea that losing weight slowly is better for you is an old wives' tale,' says Professor Nick Finer, consultant endocrinologist and an expert in obesity at University College London Hospitals.

Crash dieting is a helpful kick-start

Concerns have been raised over what crash dieting does to the body.

'On a very low calorie diet, it's unlikely you'll be able to get five portions of fruit and veg a day or three portions of calcium,' says Sian Porter of the British Dietetic Association.

'This is why some obese people who go on drastically low calorie diets have been found to be suffering from malnutrition.'

But she says slashing your food intake can be helpful as a kick-start because fast results get you motivated. However, these kinds of diets should be followed for a maximum of only 12 weeks and with advice from a doctor.

'It can help initially, but it still needs to be combined with learning new habits, such as eating because you're hungry and not for comfort,' says Jane Ogden, professor of health psychology at the University of Essex, who researches obesity.