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The Clocktowers clockThursday 5 July 2018 8:38am

Ross Wilson and Haxby Abbott image
Dr Ross Wilson (left) and Professor Haxby Abbott's research into the Body Mass Index (BMI) of New Zealanders has produced some alarming results suggesting if current trends continue, the average BMI will exceed the obesity threshold by the early 2030s.

The Body Mass Index (BMI) of New Zealanders is continuing to rise and on current trends, two million New Zealanders will be considered clinically obese by 2038 up from 1.1 million in 2015, new University of Otago research reveals.

The research published today in the Australian and New Zealand Journal of Public Health, shows the population mean BMI increased from 26.4kg/m2 in 1997 to 28.3kg/m2 in 2015. If current trends continue, New Zealand's average BMI will exceed the obesity threshold of 30kg/m2 by the early 2030s.

The results also show increasing ethnic and socioeconomic disparities with the BMI of Māori and Pacific people and those living in socially deprived neighbourhoods higher again. By 2038, the average BMI among Pacific people is projected to exceed that of the general population by 7.1-8.1kg/m2.

It has led the researchers, Dr Ross Wilson and Professor Haxby Abbott from the University of Otago's Centre for Musculoskeletal Outcomes Research at the Dunedin School of Medicine to call for public health policy measures to address the situation.

“BMI and obesity rates are continuing to increase in New Zealand and our expectation is that they will continue to do so for the foreseeable future,” Dr Wilson says.

“High BMI has now overtaken tobacco as the greatest contributor to health loss in New Zealand, which emphasises the public health importance of these findings,” he says.

The BMI is a measure of body fat based on height and weight that applies to adult men and women. Between 18.5kg/m2 and 25kg/m2 is considered the healthy weight range, anything at 30kg/m2 or above is considered obese, Dr Wilson explains.

He and Professor Abbott considered potential influences on obesity from the data of 76,294 adult New Zealanders, including the effects of an aging population and cohort effects reflecting the increased exposure of younger New Zealanders to a high-obesity environment during critical phases of childhood development, to see whether these would explain the trends in population BMI. They did not.

Instead, the researchers say the recent increases in population BMI can be attributed to “period effects”, or changes in the physical, socio-cultural or economic environments which may affect BMI by shaping behaviours such as food choice and levels of physical activity.

“These results suggest that, in the New Zealand context, the forces behind the obesity epidemic have largely been contemporaneous (period) influences on BMI, such as greater availability and consumption of high-energy, low-nutrient foods and lower levels of physical activity across all cohorts, rather than cohort-specific factors,” the researchers state in their paper.

“Altering or mitigating these environmental influences is therefore crucial to slow or reverse projected increases in population obesity.”

The findings emphasise the need for effective public health measures to address the causes of the obesity epidemic, the pair say.

“These projections imply that, unless addressed by improved public health policies, ongoing population BMI increases are likely to increase the premature mortality, population health loss, healthcare system costs and workplace productivity losses associated with the obesity epidemic.”

Tobacco control may be a useful parallel for considering the importance of comprehensive reforms across a range of policy areas (e.g. taxation, advertising restrictions, product regulation), in halting the spread of a public health epidemic, the researchers state.

“A comprehensive obesity reduction strategy might include, among other things, improving the relative affordability of healthy foods (e.g. through taxation, subsidies), restrictions on marketing of unhealthy foods and promotion of active modes of travel such as walking and cycling.”

Recent decades have seen a significant rise in New Zealanders' BMI with the country having among the highest prevalence rates of “overweight” and obesity among developed countries. Between 1977 and 2011-2013, the prevalence of obesity trebled to 30 per cent.

High BMI is the greatest contributing risk factor to health loss in New Zealand. Healthcare costs associated with treating overweight and obesity-related conditions in New Zealand were estimated to be NZ$624 million in 2006, representing 4.4 per cent of all healthcare spending. Given ongoing increases in obesity prevalence over the past decade, current obesity-related healthcare costs are likely to be substantially higher than this, the researchers say.

This research was supported, in part, by the Health Research Council of New Zealand.

For further information, contact:

Dr Ross Wilson
Centre for Musculoskeletal Outcomes Research
Tel 474 0999 ext 58613

Liane Topham-Kindley
Senior Communications Adviser
Tel 479 9065
Mob 021 279 9065

A list of Otago experts available for media comment is available elsewhere on this website.

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