WASHINGTON (Reuters Life!) What is the healthiest weight to be? People hoping for a little jiggle room may be disappointed it is the weight already identified by public health experts using body mass index or BMI.

There had been some suggestion that it may be healthier to be pleasantly plump, but the team at the U.S. National Cancer Institute crushed any such idea with a study of 1.5 million adults published on Wednesday.

The healthiest BMI is 22.5 to 24.9, they found at the upper end of where the World Health Organization, Centers for Disease Control and Prevention and other groups have said people should be.

Body-mass index is the weight in kilograms divided by the square of the height in metres. A BMI of between 25 and 30 is overweight and a BMI of 30 or over is obese.

A person 5ft 5in tall is classified as overweight at 150 pounds and obese at 180 pounds. A 5ft 10in tall person who weighs 209 pounds has a BMI of 30 and is obese.

Being overweight or obese raises the risk of heart disease, diabetes, some cancers and arthritis. The study, published in the New England Journal of Medicine, confirms that having a BMI of 25 or more also makes a person more likely to die than someone the same age who is slimmer.

“There is a small increased risk of all-cause mortality associated with being overweight about ten percent compared to having a normal BMI,” Amy Berrington de Gonzalez of the National Cancer Institute, who led the study, said in a telephone interview.

But the severely obese those with a BMI of 40 or more have 2.5 times the risk of dying than people of a healthy weight who are the same age.

The original BMI guidelines were set using some data on health, but Berrington said several recent studies had suggested that people considered overweight may be less likely to die of cancer and other conditions. So she and an international team of experts took another look at the data.

“We used 19 studies that had been conducted all over the world,” Berrington said.

One caveat they were all in mostly white, westernised populations in Europe, Australia and the United States.