The chances of an obese person recovering what, for them, is normal body weight, come in at just one in 210 for men and one in 124 for women, a study led by King's College London has found.

For people who are morbidly obese, the odds are even worse; one in 1,290 for men, one in 677 for women, the researchers say.

That suggests present weight-management strategies that focus on diet and exercise after the fact are ineffective in controlling obesity at the population level, they say in their study appearing in the American Journal of Public Health.

"Once an adult becomes obese, it is very unlikely that they will return to a healthy body weight," says study leader Dr. Alison Fildes. "New approaches are urgently needed to deal with this issue."

For the study, the researchers used electronic health records to track the weight of 129,194 men and 149,788 women to gauge the chances of obese people attaining their normal weight or even managing a 5 percent loss in body weight.

The odds of obese individuals accomplishing a 5 percent weight loss over a year's time was one in 12 men and one in 10 women, and even in those who achieved such weight loss, more than 50 percent put the pounds back on in as little as two years and 78 percent put back on the lost weight within five years, the researchers reported.

Very few were able to reach a healthy body weight; just 1,283 men and 2,245 women out of the entire study population managed to achieve that goal, they said.

"Losing 5 to 10 per cent of your body weight has been shown to have meaningful health benefits and is often recommended as a weight loss target," Fildes says. "These findings highlight how difficult it is for people with obesity to achieve and maintain even small amounts of weight loss."

The findings suggest current weight loss plans for populations at large don't appear to be working, the researchers say.

Fildes stresses that treatments should better focus on preventing individuals who are overweight or obese from gaining additional weight as well as help people who have lost weight to keep it off. However, she says that there must be also priority placed on the prevention of weight gain in general.

Co-researcher Martin Gulliford said he agreed on the necessity for re-examining priorities.

"The greatest opportunity for stemming the current obesity epidemic is in wider-reaching public health policies to prevent obesity in the population," he says.