Otago research reveals alarming rise of obesity in New Zealand
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 Body Mass Index 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 (eg, 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 (eg, 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.
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