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.
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.
How many Australian adults are overweight?
In Australia, data about weight are collected in two ways - measured and self-reported. Studies have shown that people tend to over-report their height and under-report their weight, therefore body mass data based on self-reported data are likely to be underestimates. When interpreting these data, it is important to note that rates based on self-report data should not be compared with those based on measured data.
Measured data
- 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.
Self-reported data
- Data from the 2004-05 National Health Survey showed that 47 % (7.5 million) of Australians aged over 15 years were overweight. Of these, one third (2.5 million) were obese.
- Males were more likely than females to be overweight. Some 56% of males aged 15 years or over had a BMI of 25 or more compare to 39% of females.
- For both males and females, the highest rates of those who were overweight were aged 55-64 years, 68.5% and 52.2% respectively.
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 (per cent)
| Sex, year |
Overweight but
not obese (per cent) |
Obese (per cent) |
Total overweight
and obese (per cent) |
| Boys, 1985 |
9.3 |
1.4 |
10.7 |
| Boys, 1995 |
15.3 |
4.7 |
20.0 |
| Girls, 1985 |
10.6 |
1.2 |
11.8 |
| Girls, 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
Body weight data sources in Australia
AIHW has compiled a spreadsheet that lists national data collections that include body weight and related data. Each listing shows data included in that collection plus a link to its owning organisation.
Body weight data sources in Australia
AIHW publications