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17.01.2013

Waist measurement says more about health than BMI

Are you too fat or not? You're better off answering this question with a tape measure than a weighing scale. According to obesity researchers at the Pennington Biomedical Research Center, your waist measurement says more than your BMI. They published their findings in the International Journal of Obesity.

You measure your waist at the narrowest part of your middle, placing the tape measure just above your pelvic bone. If adult women have a waist measurement of 89 cm or more they have too much fat and therefore an increased risk of diabetes and cardiovascular disease. For men the cut-off point is 102 cm.

Most nutritionists and scientists prefer not to use waist measurement as an indication that someone is too fat; they prefer to use the BMI. The Body Mass Index is calculated by dividing your bodyweight in kg by the square of your height in metres.

Another measurement is waist-hip ratio. This is waist measurement divided by hip measurement at the widest point. Men are too fat if the ratio is above 0.9; for women the cut-off point is 0.85.

There is much discussion about which criteria gives the most accurate indication of whether you need to lose weight or not. BMI is under attack because recent studies have shown that an individual with a BMI that is well within the limits, but with a bigger waist measurement is not necessarily healthy. [N Engl J Med. 2008 Nov 13;359(20):2105-20.]

The researchers at Pennington studied which of the forms of measurement – the BMI, waist measurement or waist-hip ratio – was the best predictor of mortality. They used data that had been gathered for the Canadian Heart Health Survey Follow-Up Study, in which about 8,000 men and women were monitored for an average of thirteen years. The researchers knew which participants had died and what the cause of death was. They also knew the BMI, waist circumference [WC] and waist-hip ratio [WHR].

This enabled the researchers to calculate the relationship between BMI, WC and WHR on the one hand and risk of dying on the other. The results are shown in the figures below. An asterisk indicates a statistical relationship. The more asterisks, the stronger the relationship. The message is clear: your waist measurement gives the best indication of whether you need to lose weight.

"Waist circumference consistently exhibited the most prominent association with mortality risk for all-cause, cardiovascular disease and cancer mortality compared with weaker associations for BMI and waist–hip ratio", the researchers conclude.

"Results indicate the need to account for waist circumference in examining the relationship between adiposity and mortality. The clinical importance of maintaining a low waist circumference regardless of BMI bears significant implications for preventing premature mortality attributable to cardiovascular or cancer complications."

Source:
Int J Obes (Lond). 2012 Nov;36(11):1450-4.

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