Overweight and obesity increase the risk of chronic diseases including heart attack and stroke, and are associated with increased morbidity and mortality. Excess body fat can contribute to the development of biomedical risk factors, raising levels of blood pressure and abnormal blood lipids, and increasing the risk of type 2 diabetes.
Overweight and obesity usually occur because of an imbalance between energy intake from the diet and energy expenditure through physical activities and bodily functions. This energy imbalance is influenced by a complex interplay of individual, environmental and societal determinants (AIHW 2017).
Adults with a body mass index (BMI) (kg/m2) of 25–29 are considered to be overweight but not obese, while a BMI of 30 or over is classified as obese. A separate classification of overweight and obesity based on age and sex is used for children and adolescents.
In 2017–18, based on measured data from the 2017–18 National Health Survey:
- an estimated 25% children and adolescents aged 2–17 were overweight or obese, with 17% overweight but not obese, and 8.2% obese. Rates varied across age groups, but were similar for males and females (AIHW 2020)
- an estimated 2 in 3 (67%) Australians aged 18 and over were overweight or obese (36% overweight but not obese, and 31% obese)
- men had higher rates of overweight and obesity than women (75% men, 60% women), and higher rates of obesity (33% men, 30% women)
- obesity is more common in older age groups—16% of adults aged 18–24 were obese, compared with 41% of adults aged 65–74.
After adjusting for different population age structures over time, the prevalence of overweight and obesity among Australians aged 18 and over increased from 57% in 1995 to 67% in 2017–18. This was largely due to an increase in obesity rates, from 19% in 1995 to 31% in 2017–18 (Figure 1).
Figure 1: Distribution of BMI among persons aged 18 and over, 1995 and 2017–18