The 'baloney mass index': Why U.S. obesity epidemic is far worse than previously thought
Combining BMI with blood test to measure levels of key protein would be 'more accurate'

PUBLISHED:

10:39 GMT, 4 April 2012

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UPDATED:

10:46 GMT, 4 April 2012

Overweight or obese BMI underestimates how fat a person is in nearly half of cases

Overweight or obese BMI underestimates how fat a person is in nearly half of cases

The obesity problem in the U.S is far worse than previously thought, according to a study.

Researchers found 39 per cent of Americans currently classed as slightly overweight using the Body Mass Index calculator are probably obese.

The team from Weill-Cornell Medical College in New York said the measurement – that combines a person's height and weight to diagnose obesity – often underestimated actual fat levels.

The authors calculated the BMI of more than 9,000 adults at a private clinic in New York. They then took Dual Energy X-ray Absorptiometry (DXA) scans, which measures body fat, muscle mass, and bone density simultaneously.

They found 65 per cent of patients were classed as obese by DXA but only 26 per cent of patients were obese according to BMI.

Study co-author Dr Eric Braverman, said: 'The Body Mass Index is an insensitive measure of obesity, prone to under-diagnosis, while direct fat measurements are superior because they show distribution of body fat.'

He added it should be called the 'baloney mass index' as it got the results wrong nearly half the time.

He said that BMI was particularly inaccurate when assessing older women.

HOW IS BMI CALCULATED

The most widely used way to measure an adult's weight is to calculate body mass index (BMI).

This is your weight in kilograms divided by your height in metres squared.

If your BMI is between 25 and 29.9, you are over the ideal weight for your height (overweight).

If your BMI is between 30 and 39.9, you are obese.

If your BMI is over 40, you are very obese (known as ‘morbidly obese’).

However, this method can't take into account if you are muscular.

Reporting in the open access journal PLoS ONE researchers recognised that BMI was a convenient, low cost and safe way of calculating a person's weight. It is the most widely used way to measure weight in the U.S and UK.

However, the authors said the outdated mathematical equation needed to evolve to correctly evaluate body fat.

'These estimates are fundamental to U.S. policy addressing the epidemic of obesity and are central to designing interventions aimed at curbing its growth,' the authors said, 'yet the [current policies] may be flawed because they are based on the BMI.'

The authors said levels of leptin, a hormone protein, are strongly correlated to body fat.

They suggested that if DXA was deemed to expensive that leptin levels could be used alongside BMI to create a more accurate picture of obesity.