Obesity in New Zealand
Question and Answer

What is obesity?
Obesity is defined as an excessively high amount of body fat (adipose tissue) in relation to lean body mass. Overweight is excess weight for height.

How is obesity measured?
Body mass index (BMI) is commonly used to classify adults as overweight and obese. BMI is a measure of weight adjusted for height and is calculated by dividing weight in kilograms by height in metres squared (kg/m²).

In New Zealand, obesity is defined as:

• BMI greater than or equal to 30.0 for European, Other and Asian adults
• BMI greater than or equal to 32.0 for Maori and Pacific adults.

Overweight is defined as:

• BMI 25.0 to 29.9 for European, Other and Asian adults
• BMI 26.0 to 31.9 for Maori and Pacific adults.

Why are overweight and obesity a problem?
Overweight and obesity are risk factor for most serious chronic diseases, including type 2 diabetes, ischaemic heart disease (IHD), stroke and several common cancers.

The impact of excess body weight on these diseases operates, at least in part, through its effects on insulin resistance, blood glucose, blood lipids and blood pressure.

In an earlier (2003) study carried out jointly by the Ministry of Health and the University of Auckland, higher than optimal BMI was estimated to contribute to approximately 3200 deaths in New Zealand in 1997, mostly through type 2 diabetes, IHD and stroke. This burden will be even higher today given that the mean BMI of the adult population has increased since 1997.

What causes overweight and obesity?
Overweight and obesity are the result of a positive energy balance – that is, a chronic excess of energy intake (food and beverage consumption) over energy expenditure (physical activity).

Although some people are more genetically susceptible to weight gain than others, the rapid increase in the prevalence of obesity in recent years has occurred too quickly to be explained by genetic changes and most experts believe it is due to living in an increasingly ‘obesogenic’ environment – one that promotes overconsumption of food and drinks and limits opportunities for physical activity.

Where did the data come from?
The BMI data are derived from measured weight and height among adults aged 15-74 years from four cross-sectional national nutrition and health surveys: the 1977 National Diet Survey (n=1761), 1989 Life in New Zealand Survey (n=2924), 1997 National Nutrition Survey (n=4100), and 2002/03 New Zealand Health Survey (n=10813).

How many adults are overweight or obese?
Approximately 500,000 adult New Zealanders are obese and a further 900,000 are overweight.

What is the Ministry of Health doing about obesity?
Reducing obesity is one of the priority objectives in the New Zealand Health Strategy, along with improving nutrition and increasing physical activity. These three objectives have been combined into the Healthy Eating – Healthy Action Strategy.

The HEHA strategy recognises that it will take multiple actions by multiple players over many years to change the environment so that healthy choices are the easy choices.
In recognition of this, the HEHA implementation plan (June 2004) was developed in partnership with other central government agencies, health-related non-government organisations, academia and industry.

When will new data on obesity be available?
Data on measured BMI and the prevalence of obesity will be collected in the next round of health and nutrition surveys.