What is obesity?

Obesity is a condition where you carry excess body fat that can frequently cause medical problems, such as  heart disease, diabetes and high blood pressure. It results from a number of genetic and lifestyle factors. If someone is obese, their heart is working harder to pump blood around their entire body which puts pressure on the organ.

The distribution of fat is also important when assessing obesity. For example; abdominal obesity (excess fat around your waist) is related to a higher risk of cardiovascular disease and type 2 diabetes.

What are the symptoms of obesity?

People with a body mass index (BMI) of 30 or more are classified as obese. Obesity is commonly measured by this index, which adjusts you weight for your height

Your BMI is calculated by dividing your weight (in kilograms) by the square of your height (in metres). The ranges below show healthy, at risk and unhealthy BMI levels:

  • Underweight = Below 18.5 BMI
  • Normal = 18.5 – 24.9 BMI
  • Overweight = 25.0 – 29.9 BMI
  • Obese (Class I) = 30.0-34.9 BMI
  • Obese (Class II) = 35.0 – 39.9 BMI
  • Extreme obesity (Class III) = 40.0 and above BMI

Calculate your BMI below


What are the causes of obesity?

Obesity occurs when you consume more calories than you burn. While there are genetic, behavioural and hormonal influences that can affect body weight, the main causes of obesity are:

  • Inactivity: If you’re not active and have a sedentary lifestyle, you will not burn as many calories as you consume through exercise or normal daily activities.
  • Unhealthy diet and eating habits: If you have an unhealthy diet full of junk food and/or soft drinks or high calorie drinks, weight gain is inevitable. 

How is obesity diagnosed?

The best way to detect whether you are obese is to calculate your BMI as. If you are in the obese range, your doctor may want to perform some further tests to determine how much weight you need to lose and what health conditions you are at risk of. These additional tests may include:

  • Taking your health history
  • Doing a general physical exam
  • Measuring your waist circumference
  • Checking for other health problems like high blood pressure or diabetes
  • Blood tests

How can obesity be treated?

The goal of obesity treatment is to lose and maintain a healthy weight. All reputable weight-loss programs require lifestyle changes through eating habits and physical activity, and will be tailored to suit individual needs. Treatment tools include:

  • Dietary changes
  • Increase in physical exercise
  • Behaviour therapy such as counselling or support groups
  • Weight loss surgery (this is a last resort) 

How can you prevent obesity?

It is important to be mindful of the ways you can prevent excess weight gain, whether you are a healthy weight or at risk of obesity. The steps to prevention include:

  • Exercise regularly, starting with daily walking
  • Eat a healthy diet - keeping your cholesterol in check
  • Avoid foods and beverages high in saturated fats and trans-fats
  • Minimise sugar intake
  • Monitor your weight

Ask your doctor for a heart health check which looks at the key risk signs. Download our Heart Health Guide Guide to take with you to your next doctor's appointment.

Research into ObesityDonate to heart researchHow to prevent heart diseaseLearn about other heart diseases

Acknowledgement of Country

The Victor Chang Cardiac Research Institute acknowledges the traditional custodians of the land, the Gadigal of the Eora nation, on which we meet, work, and discover.
Our Western Australian laboratories pay their respect to the Whadjuk Noongar who remain as the spiritual and cultural custodians of their land.