BMI could be missing obesity risks

Reported 25 Feb 2011

Nutrition expert Dr Margaret Ashwell, Visiting Fellow, Oxford Brookes University Ashwell, argues that using BMI alone could be missing some patients at risk of the diseases associated with obesity.

While body mass index (BMI) is a good proxy for total body fat, it does not distinguish between different types of fat distribution or take into account people who are unusually muscular.

Excess fat on the stomach, giving the ‘apple’ shape is often associated with risk factors for serious conditions such as heart disease, raised blood pressure and diabetes while fat under the skin, around the bottom, hips and thighs (pear shape) is less harmful.

For more than a decade, I have argued that risk for various disease should be based on waist-to-height ratio (WHtR) – that your waist circumference should not be more than half your height (WHtR 0.5).

My colleagues and I reviewed 78 studies in 14 countries confirming that WHtR is a better predictor of cardiometabolic risk than BMI.

The WHtR measurement could be used to assess risk for adults in several ethnic groups because the BMI boundary values were derived from Caucasian populations.

WHtR might also be a simple way to assess health risk in children.

Our research – applying the WHtR boundary value of 0.5 to nearly 2,000 British adults – found that a third of non-overweight men and one in seven non-overweight women had a WHtR value greater than 0.5.

It remains a concern that using BMI alone for screening could miss people who are at risk.

Yet it may also alarm those who are not at risk as it appears from their BMI.