What is obesity?


Worldwide, obesity kills almost 3 million people each year.2

Obesity is now widely considered a chronic disease.1

Explore this website to further understand the science behind obesity. Then visit your GP to discover science based treatment options.

What you need to know

  • Obesity is now recognized worldwide as a chronic disease with severe health and quality of life consequences.1-3
  • Misinformation and misunderstandings of obesity’s scientific causes and treatments are widespread.3
  • The stigma of obesity means people are wrongly blamed by society for their disease and discriminated against.2,4

Calculate your Body Mass Index (BMI)

Body mass index, or BMI, is a calculation based on your height and weight to place you in a weight category: underweight, normal weight, overweight, or obese.5,6,7

BMI is a very general measure that places you in 1 of 6 broad weight categories – underweight, normal weight, overweight, obese.8


Your BMI is
Weight classification: Obese III Risk of related disease: Very severe risk

Below 18


Increased risk of comorbidity

18 - 25

Normal weight

Low risk of comorbidity

25 - 30


Increased risk of comorbidity

30 - 35

Obese I

Moderate risk of comorbidity

35 - 40

Obese II

Severe risk of comorbidity

40 - 45

Obese III

Very severe risk of comorbidity

BMI classes and comorbidity risks8

Classification BMI Risk of Comorbidities


Less than 18


Normal weight

18 – 25





Obese I



Obese II



Obese III

40 or greater

Very severe

Understanding obesity


Learn more


1. Bray G, et al. Obesity: a chronic relapsing progressive disease process. A position statement of the World Obesity Federation, Obesity Rev 2017; 18(7); 715–23.

2. Wolfenden L, et al.  The challenge for global health systems in preventing and managing obesity. Obesity Reviews. 2019;(S2):185–193.

3. Caterson I, et al. Gaps to bridge: Misalignment between perception, reality and actions in obesity, Diabetes Obes Metab 2019; 21(8): 1914–24. 

4. Oldham M, Robinson E. Visual body size norms and the under-detection of overweight and obesity. Obes Sci Pract 2017; 4(1): 29–40.

5. RACP. Action to prevent obesity and reduce its impact across the life course – Evidence Review. 2018. Available at https://www.racp.edu.au/docs/default-source/advocacy-library/racp-obesity-position-statement.pdf

6. Bray G, et al. The Science of Obesity Management: An Endocrine Society Scientific Statement. Obesity Rev 2018; 39; 79-132

7. ANZOS and ADS. 2019. The Australian Obesity Management Algorithm. Available at: http://anzos.com/assets/Obesity-Management-Algorithm-18.10.2016.pdf. Accessed September 2019.

8. RACGP Smoking, nutrition, alcohol, physical activity (SNAP): A population health guide to behavioural risk factors in general practice, 2nd edition. Melbourne: Available at https://www.racgp.org.au/FSDEDEV/media/documents/Clinical%20Resources/Guidelines/SNAP-guideline.pdf. Accessed December 2019.