Bad news for people trying to lose weight -- a new assessment of how the body responds to dieting shows that it is about twice as difficult as previously thought to shed fat.

The calculations also puncture the myth that cutting calories will lead to continued weight loss.

In fact, the effect of reducing the intake of calories levels off after about three years, scientists say.

Obesity experts had previously suggested that cutting 100 calories a day from the diet for six months would lead to the loss of about 5lb in weight.

But it turns out that such a loss is more likely to take a year and that any further weight loss will reach a plateau after three years.

"People have used this rule of thumb for how to lose weight for decades and it turns out to be completely wrong," said Kevin Hall, a mathematical modeller at the US National Institute of Diabetes and Kidney Diseases in Maryland.

"It doesn't account for the metabolic changes that take place when people change their diet. If you cut the calories in someone's diet, the metabolism slows down."

A popular misconception is that overweight or obese people have a slower metabolism. In fact, the fatter someone was, the higher their metabolism was likely to be, Dr Hall said.

The rule of thumb for losing weight under the new findings is to cut 10 calories per day from your diet for every pound you want to lose.

_{(© Independent News Service)}