New York - The obesity epidemic could be far worse than previously realised because of serious flaws in the way body fat is measured, according to a study.
Researchers said the Body Mass Index - the formula usually used to determine fat - drastically underestimated how many people should regard themselves as unhealthily overweight or obese.
More than a third of adults in the US are considered obese.
But the New York study concluded that 39 percent of Americans were being classified as overweight on the basis of their BMI when they were actually obese.
The study’s authors, Dr Eric Braverman, of Weill Cornell Medical School, and Dr Nirav Shah, the New York state health commissioner, calculated the BMI - weight in kg divided by height in metres squared - of nearly 1,400 adult patients at a private health clinic.
They then compared the results with those of a more sophisticated measurement, a blood test combined with a Dual Energy X-Ray Absorptiometry (DXA) scan, which measures a person’s body fat, muscle mass and bone density.
The comparison found BMI wrongly classified half of the women, and one in four men.
While only 26 percent of the patients were classed as obese according to BMI, 65 percent of them fell into that category when measured with the DXA scan. Dr Braverman said BMI should be called the “baloney mass index” because it was so inaccurate.
“The Body Mass Index is an insensitive measure of obesity, prone to under-diagnosis,” he said.
The study found BMI was especially prone to underestimating obesity in women.
In addition, the likelihood of error increased as they got older.
Fifty-nine percent more women aged 70 or over were classified as obese when measured with a DXA scan then their BMI suggested.
Researchers said this was because women lost more muscle to fat than men as they age.
As BMI does not distinguish between muscle and fat, it doesn’t pick up on the change.
“BMI does not tell you how much fat you have,” Dr Braverman added. - Daily Mail