What is overweight and obesity?

Overweight and obesity refers to excess body weight. Excess weight, especially obesity, is a major risk factor for chronic conditions such as cardiovascular disease, type 2 diabetes, high blood pressure, asthma, back pain and some cancers. Overweight and obesity is also associated with higher rates of death (AIHW 2017).

In 2015, 8.4% of the total burden of disease in Australia was due to overweight and obesity (AIHW 2019). Overweight and obesity was the leading risk factor contributing to non-fatal burden (living with disease) (see the Australian Burden of Disease Study 2015: Interactive data on risk factor burden for more information).

Collecting information on overweight and obesity is important for managing associated health problems.

Body mass index (BMI)

Body Mass Index (BMI) is an internationally recognised standard for classifying overweight and obesity in adults. BMI is calculated by dividing a person’s weight in kilograms by the square of their height in metres. BMI does not necessarily reflect body fat distribution or describe the same degree of fatness in different individuals. At a population level however, BMI is a practical and useful measure for identifying overweight and obesity.

This report uses measured height and weight for calculated BMI values, as self-reported values are less accurate.

This body mass index (BMI) calculator allows you to calculate your BMI by entering your sex, height and weight. These graphs show the distribution of BMI values by sex and the proportion of men and women in each BMI category in 2017–18. The most common category is normal weight (39%) for women and overweight but not obese (42%) for men.

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Table 1: BMI classification in adults
BMI (kg/m²) Classification
Less than 18.5 Underweight
18.5 to less than 25 Normal weight
25 or more Overweight or obese
25 to less than 30 Overweight but not obese
30 or more Obese
30 to less than 35 Obese class I
35 to less than 40 Obese class II
40 or more Obese class III

Source: WHO 2000.

Waist circumference

Waist circumference is an alternative way to assess the risk of developing obesity-related chronic diseases. A higher waist measurement is associated with an increased risk of chronic disease. The risk levels presented below are for Caucasian men, and both Caucasian and Asian women.

Table 2: Waist circumference associated with increased risk of metabolic complications

Sex

Increased risk

Substantially increased risk

Men

94 cm

102 cm

Women

80 cm

88 cm

Source: NHMRC 2013.

For information on how to correctly measure your waist, visit the National Heart Foundation website.

Measuring overweight and obesity in children and adolescents

Height and body composition are continually changing for children and adolescents. A separate classification of overweight and obesity based on age and sex is used for children and adolescents (Cole et al. 2000).