August 18, 2006
Study finds standard “obesity” test badly flawed
LONDON (Reuters) - Body Mass Index (BMI), the standard
measure of obesity, is badly flawed and a more accurate gauge
should be developed, according to doctors in the United States.
Writing in Friday's Lancet medical journal, the researchers
from the Mayo Clinic College of Medicine, Rochester, Minnesota,
found that patients with a low BMI had a higher risk of death
from heart disease than those with normal BMI.
At the same time overweight patients had better survival
rates and fewer heart problems than those with a normal BMI.
This apparently perverse result, drawn from data from 40
studies covering 250,000 people with heart disease, did not
suggest that obesity was not a health threat but rather that
the 100-year-old BMI test was too blunt an instrument to be
"Rather than proving that obesity is harmless, our data
suggests that alternative methods might be needed to better
characterize individuals who truly have excess body fat
compared with those in whom BMI is raised because of preserved
muscle mass," said lead researcher Francisco Lopez-Jiminez.
About 30,000 people in Britain die due to obesity every
year and 300,000 in the United States where the condition is
now thought to have overtaken smoking as the main cause of
Body Mass Index, invented by Belgian polymath Adolphe
Quetelet between 1830 and 1850, is a measure of body fat
calculated from height and weight.
A figure of less than 18.5 is considered underweight, while
from 18.5 to 24.9 is normal, 25 to 29.9 is overweight and
anything over 30 is categorized as obese.
Intended as a broad indicator of general health, it has
become a standard diagnostic tool of heart disease risk.
Maria Grazia Franzosi from the Instituto Mario Negri in
Milan, writing in the same issue of the Lancet, noted that a
52-country study comparing four different tests -- BMI,
waist-to-hip ratio, waist measure and hip measure -- found that
waist-to-hip was the best predictor of heart attack risk.
"BMI can definitely be left aside as a clinical and
epidemiological measure of cardiovascular risk," she said.
"Uncertainty about the best index of obesity should not
translate into uncertainty about the need for prevention policy
against excess bodyweight," she cautioned.