BMI hides obesity, waist better measure, Deakin University and Monash University study finds

BODY mass calculators are not detecting the full scale of Australia’s obesity problem, as new data shows average waist circumference is increasing faster than overall weight gain.

New data shows the average waist circumference of Australians is increasing faster than overall weight gain. Picture: istock

BODY mass calculators are not detecting the full scale of Australia’s obesity problem, as new data shows average waist circumference is increasing faster than overall weight gain.

Deakin and Monash University researchers are now working to uncover the “why” — and determine if we are now carrying more fat and less lean muscle for the same weight, or if we are changing from the “pear” shape en masse towards the more dangerous “apple” silhouette.

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They compared the weights and heights of more than 18,000 adults across three population studies in 1989, 2000 and 2011-12, finding women were typically 5.4kg heavier and had a 10.7cm larger waist in the most recent weigh-in. Men increased their weight by 7kg and waist by 7.3cm over the 23 years.

Average waist circumference is increasing faster than overall weight gain.

Waist circumference increased by 6.7cm in women and 2.8cm in men on top of what was expected from projected weight increases across all ages, weight ranges and smoking status.

And while the prevalence of obesity increased by 25 per cent for women and 21 per cent for men over the two decades, regardless of whether it was measured by body mass index or in combination with waist size — BMI grew particularly unreliable for women.

It failed to detect 20 per cent of obese women in the most recent measure.

The findings were published in the journal Preventative Medicine.

Lead author Emma Gearon, research fellow at Deakin’s Global Obesity Centre and PhD candidate at Monash, said the results showed that using BMI alone missed an increasing proportion of people categorised as obese according to waist circumference.

Given that obesity is a leading contributor to disease, Ms Gearon said it was vital that it was accurately measured.

“We know that around the globe we tend to rely on BMI to monitor the prevalence of obesity, but I’d like to see that change,” she said.

“We now need to work out if we need to replace BMI or have waist circumference as an additional measure.”

Baker Heart and Diabetes Institute Professor John Dixon, who has researched obesity for 20 years, said the public should be “very concerned” about a trend of carrying more weight around our middle, as it increased the risk of hypertension, heart disease and type 2 diabetes.

“Until we address it as a major public health matter we’re not going to win,” Prof Dixon said.

@BrigidOConnell

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