Overweight and obesity

People who are overweight, and particularly those who are obese, have higher rates of death and illness than people of healthy weight, both overall and from a range of specific conditions. These include cardiovascular disease, high blood pressure, Type 2 diabetes, sleep apnoea, osteoarthritis, psychological problems and reproductive problems for women.

What is considered overweight?

The body mass index (BMI) is an internationally recognised standard for classifying overweight and obesity in adults. BMI is calculated by dividing the weight in kilograms by the square of the height in metres. For people aged 18 years and over, a BMI of 25 or more is considered overweight, and 30 or more is obese.

For children and adolescents, a separate classification of overweight and obesity based on age and sex is recommended as height and body composition are continually changing.

More information on BMI is given in the FAQs page.

Causes of overweight

While many factors may influence an individual's weight, overweight and obesity is due mainly to an imbalance of energy intake from the diet and energy expenditure through physical activity. Genetic and environmental factors play a role, but attention to diet and physical activity is important not only for preventing weight gain, but also for weight loss and subsequent maintenance.

More information is found at the Nutrition and Physical Inactivity pages.

How many Australian adults are overweight?

• The 1999-2000 Australian Diabetes, Obesity and Lifestyle Study indicated over seven million adult Australians aged 25 years and over (60%) were overweight. Of these, over two million (21%) were obese.
• Men were more likely than women to be overweight, with 67% of men compared with 52% of women (aged 25 years and over) being overweight.
• There have been significant increases in the proportions of overweight and obese Australians over the last 20 years. From 1980 to 1999-2000, for people aged 25-64 years, the proportion of overweight women increased from 27%  to 47%, and the proportion of overweight men increased from 47% to 66%.
• On average, women in 1999 weighed 4.8 kg more than their counterparts in 1980, and men 3.6 kg more.

How many Australian children and adolescents are overweight?

Data collected in 1995 indicate the proportion of overweight or obese children and adolescents aged 2-17 years was 21% for boys and 23% for girls.

In the ten year period between 1985 and 1995, there was an increase in the proportion of children who were either overweight but not obese, or obese.

Prevalence of overweight and obesity in children and adolescents aged 5 - 17 years
	Overweight but not obese	Obese	Total overweight and obese
		Percent
Boys
1985	9.3	1.4	10.7
1995	15.3	4.7	20.0
Girls
1985	10.6	1.2	11.8
1995	16.0	5.5	21.5
Source: Magarey AM, Daniels LA & Boulton JC 2001. Prevalence of overweight and obesity in Australian children and adolescents: reassessment of 1985 and 1995 data against new standard international definitions. Medical Journal of Australia 174:561-4

For more information see the data briefing: A rising epidemic: obesity in Australian children and adolescents.

More information

The AIHW has released a number of bulletins and a data briefing on overweight and obesity in Australia, with information on:

• the prevalence of and trends in overweight in Australia, see: A growing problem. Trends and patterns in overweight and obesity among adults in Australia, 1980 to 2001.
• how prevalence of and trends in overweight in Australia vary for different groups of the population, see: Are all Australians gaining weight? Differentials in overweight and obesity among adults, 1989-90 to 2001.
• older Australians, see: Obesity trends in older Australians.
• how health-characteristics of Australians vary with body weight, see: Health, wellbeing and body weight: characteristics of overweight and obesity in Australia, 2001 and Physical activity, diet and body weight: results from the 2001 National Health Survey.

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Last reviewed by on 8 December 2004