Measuring the health risks of obesity - is there a better method than Body Mass Index?

Research shows that the waist-to-height ratio measure of obesity is a better predictor of mortality risk than the commonly used Body Mass Index.

Obesity is a sizeable problem. High levels of body fat is associated with an increased risk of life threatening diseases, such as cancer and diabetes. Over recent decades ever more people are being classed as obese, giving policy makers much to ponder, as it is a topic that is important to the planning of health care, social policy, and insurance in Britain.

The measure of obesity most commonly used, and most widely known, is the Body Mass Index (BMI). To arrive at a person's BMI score, their weight in kilograms is divided by the square of their height in metres. This method has flaws. For example, BMI overestimates fat in muscular people, and it cannot give information about fat distribution.

Alternative methods for measuring obesity focus on waist measurements. The use of waist-to-height ratio (WHtR) for detecting central obesity, and health risks associated with it, were first proposed in the mid 1990s. WHtR is a better proxy for central fat, which has greater associated health risks than fat stored in other parts of the body. The paper Waist-to-Height Ratio Is More Predictive of Years of Life Lost than Body Mass Index contends that WHtR is also a better measure of the health risks associated with obesity than BMI.  

The study used data from the cross sectional Health Survey for England (HSE) and the prospective Health and Lifestyle Survey (HALS), comparing the numbers of years of life lost (YLL) at three ages: 30, 50, and 70 – before comparing life expectancies between the two obesity measurements using the HSE, HALS, and 2006 UK interim life tables.

The research aimed to estimate YLL in an obese individual where obesity was measured either by BMI or WHtR. The effects of obesity on life expectancy at representative ages and for each gender separately were calculated. It found that central obesity, as measured by WHtR, was a better predictor of mortality and YLL than BMI.

Overall the results suggest that years of life lost increase dramatically when individuals exceed a WHtR of half.

This study conveys a simple message ‘‘Try to keep your waist circumference to half your height’’

The evidence presented in the paper suggests that government policy and future research should place more emphasis on WHtR as a screening tool. Focusing on WHtR will identify those with central obesity and will guide allocation of resources to those most at risk.

The research concludes that WHtR is the more valuable measure for health screening, for delivering public health policies, and estimating the burden of obesity on society. The use of WHtR in public health screening, with appropriate action, could help add years to longevity.

The published version of the paper is available for download at the link below.


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