Overweight and obesity

Body mass index

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. Height and body composition are continually changing for children and adolescents as they grow. Different BMI cut-off points based on age and sex are used when assessing children’s BMI at a population level (Cole et al. 2000). For information on BMI ranges, see Body mass index.

BMI is a tool intended for population health monitoring. It can be used to assess trends and make comparisons across time, geographical areas and groups of people at the population level. However, at an individual level, there are limitations to BMI for measuring whether someone’s weight is in a healthy range for their height (Heart Foundation 2026).

BMI does not directly measure body fat (National Academies of Sciences Engineering and Medicine 2023) and does not reflect body fat distribution or describe the same degree of fatness (adiposity) in different individuals. It does not take into account other important factors like age, gender and body composition. For example, some populations and individuals, such as athletes, do not have large amounts of adiposity; however, the contribution of increased muscle mass to weight (and overall body mass) may describe them as obese. BMI also does not consider age, sex or bone structure; research indicated the lack of this information can introduce misclassification problems that may result in bias when estimating the effects related to obesity (Rothman 2008). 

BMI is also not a good overall indicator of health. It is unable to fully capture cardiovascular and metabolic health risks (Neeland et al. 2019). It can misrepresent the burden of visceral fat, which is a type of fat that builds up around vital organs such as the heart, liver, pancreas and intestines (Neeland et al. 2019). Many health and metabolic abnormalities are associated with excess visceral fat, such as type 2 diabetes, hypertension, coronary heart disease and stroke (Neeland et al. 2019). Therefore, BMI alone is limited in measuring and assessing obesity-related morbidity and mortality risk in individuals.

Despite these limitations, BMI is still the most used and easily accessible tool as using more sophisticated methods, such as imaging to assess body fat distribution, is challenging and prohibitive in most clinical settings (Neeland et al. 2019; Cameron et al. 2020). There are simple anthropometric measures, such as waist circumference or hip circumference, that are more reflective of adipose tissue distributions and can provide better indications of obesity related chronic diseases, as well as risks of premature death (Neeland et al. 2019; Cameron et al. 2020). For more information, see Waist circumference.

The use of BMI has also recently been reported to foster weight-based discrimination and stigma and creates barriers and delays to accessing treatment, especially for those with eating disorders (Butterfly Foundation 2021). Eating disorders are serious, complex mental illnesses and both patients with low and high BMI are equally susceptible to disordered eating (Ramaswamy and Ramaswamy 2023). The diagnosis and provision of treatment for eating disorders should not be based solely on a physical indicator, such as BMI (Ramaswamy and Ramaswamy 2023).

For more information on weight stigma and eating disorders and disordered eating, see Weight stigma.

Waist circumference

Waist circumference is an alternative measure that is a better indicator than BMI of body fat distribution and the risk of developing obesity related chronic diseases. A higher waist measurement is associated with an increased risk of chronic disease. The thresholds at which waist circumference indicate an increased risk of developing disease are dependent on gender and ethnicity (NHMRC 2013). For more information on waist circumference measurement risk levels, see Waist measurement. For information on how to correctly measure your waist, visit the Heart Foundation website.

There are, however, some limitations to using waist circumference. For example, the threshold may be less accurate in some situations, such as pregnancy and medical conditions where there is distension of the abdomen (Heart Foundation 2023). Additionally, waist circumference may not accurately reflect visceral fat and subcutaneous fat accumulation (Rubino et al. 2025). Addition of biochemical markers, such as plasma triglyceride (a type of fat found in blood) to the measurement of waist circumference could help in identifying excess visceral fat and therefore identifying high–risk overweight and obese individuals (Neeland et al. 2019).

Clinical obesity definition

In 2025, the Lancet Diabetes & Endocrinology Commission redefined obesity as a disease, termed clinical obesity (Rubino et al. 2025). To date, clinical obesity terminology has not been adopted in Australia by clinicians and there are no sources of data that enable reporting.

Clinical obesity is defined as a chronic systemic illness characterised by reduced function of tissues, organs or the whole organism, directly caused by excess adiposity (fatty tissue), independent of the presence of other obesity-related diseases (Rubino et al. 2025).

It has been proposed that the reframing of obesity as an illness could allow for a more objective view of obesity. This could shift focus away from the harmful view that weight gain and management of weight gain is solely a personal responsibility, which could assist with enabling public health policies (Rubino et al. 2025).