Weight-loss guidelines have long counselled dieters that kilos shed too quickly are likelier to creep back than those lost at a slower pace.
But an Australian study, published on Wednesday, says this is wrong.
Over the long term, fast-track and slow-track dieters are equally likely to regain most of the weight they lost, according to a paper published in The Lancet Diabetes & Endocrinology.
Research led by Joseph Proietto of the University of Melbourne divided 204 obese men and women into two groups.
One group entered a weight-loss programme of 12 weeks, the other a more gradual 36 weeks.
The 12-week group were restricted to a diet of 450-800 calories per day, while the other group had their energy intake reduced by about 500 calories per day.
Those who lost 12.5 per cent or more of their bodyweight from both groups were then placed on a three-year maintenance diet.
By the end of the trial, individuals in both groups had regained some 71 per cent on average of the kilos they had shed.
"By contrast with the widely-held belief that weight lost rapidly is more quickly regained, our findings show that regain is similar after gradual or rapid weight loss," the team said.
"Our data should guide committees that develop clinical guidelines for the management of obesity to change their advice," they added.
Dieters are generally told that a weight loss tempo of no more than 500 grammes (1.1 pounds) per week is best.
The researchers noted some interesting short-term differences in how the two groups responded.
Among the fast-dieting group, more achieved their weight loss target -- 81 per cent compared to half of the other group -- and fewer left the programme.
These initial successes may be partly explained by a process called ketosis which kicks in with low-calorie intake -- the body burns fat to produce breakdown products called ketones, which are known to suppress hunger.
"Losing weight quickly may also motivate participants to persist with their diet and achieve better results," said the authors.
But this made no difference in the longer term, with the weight piling up again over time.
"For weight loss, a slow and steady approach does not win the race," Corby Martin and Kishore Gadde of the US-based Pennington Biomedical Research Center said in a comment.
"The myth that rapid weight loss is associated with rapid weight regain is no more true than one of Aesop's fables."
In comments distributed by the London-based Science Media Centre, nutritionists said the study reiterated that sustained weight loss remained a challenge, however it is achieved.
"While weight loss is hard, weight loss maintenance is even harder," said Nick Finer, an endocrinologist from University College London Hospitals.
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