Weight guidance should be redrawn for different ethnic groups to improve health, say researchers.
A study has suggested the upper limit for a healthy body mass index (BMI) should be lower for Aborigines to prevent glucose intolerance and cases of Type 2 diabetes.
BMI is calculated by dividing weight in kilograms by the square of your height in metres.
A BMI of between 20 and 25 is considered healthy, 25 to 30 overweight, and over 30 obese.
There is data to suggest that the BMI range that has been worked out on the Caucasian population doesn't necessarily apply to other ethnic groups
Dr Jeremy Krebs, Medical Research Council
BMI scores are thought to be a better indicator of how much extra weight a person carries around than weight alone as people of the same age and weights vary in height.
But the guidelines were calculated for Caucasians and experts now say different BMI limits should be set for other ethnic groups.
For example, blacks may be more sensitive to the health effects of excess weight that whites.
Researchers from the University of North Carolina (UNC) led the study.
They calculated BMIs for 2,626 aborigines in 15 remote areas in Australia.
They also looked at levels of diabetes and the impaired glucose tolerance (IGT) that precedes it.
To measure IGT, they looked at how the Aborigines processed glucose while fasting and two hours after eating.
'Astounding'
It was found the risk of developing diabetes was four times higher for those with BMIs of 22 or more.
Even those with a BMI of 22 to 25 had a three times higher risk than those with lower scores.
Dr Mark Daniel, assistant professor of health behaviour and health education at the UNC School of Public Health, led the research.
He said: "We calculated that if we could prevent gains in BMI beyond 22, we could prevent an estimated 46% of diabetes cases and 34% of impaired glucose tolerance cases, which is just astounding.
He added: "The world health community might want to revise the recommended upper healthful limit downward.
"Especially among such groups as American and Canadian Indians, Pacific Islanders, Africans and U.S. blacks and many indigenous people, who all appear to be at increased risk.
It is a problem that needs to be urgently addressed
Diabetes UK
"We believe programs to reduce the risks of diabetes are urgently needed in many parts of the world, including Australia and the United States."
Dr Jeremy Krebs, an endocrinologist and clinical scientist at the Medical Research Council centre for human nutritional research in Cambridge told BBC News Online.
"There is data to suggest the BMI range that has been worked out on the Caucasian population doesn't necessarily apply to other ethnic groups.
"There are differences in body composition between ethnic groups, differences in the proportion of fat to lean body tissue such as bone and muscle.
"At a lower BMI, they might have the same proportion of body fat that a Caucasian would have at a higher BMI.
"So their risk of conditions such as diabetes increases from a lower level."
Risk factors
A spokesman for Diabetes UK told BBC News Online: "One of the major factors contributing to the growing problem of diabetes is people being overweight and inactive.
"It is a problem that needs to be urgently addressed.
"It is also important that people are aware of other risk factors for diabetes, for example people for Asian and African Caribbean background in the UK are up to five times more likely to have the condition than white populations.
"Doctors need to consider all these risk factors when assessing people so that action can be taken to delay the onset or to ensure early identification of diabetes."
The research is published in the journal Diabetes Research and Clinical Practice.
