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Being overweight or obese increases your risk of coronary artery disease, other cardiovascular diseases and related conditions such as type 2 diabetes.

For the past 30 years, Australians have been getting progressively heavier, and we now have among the highest levels of overweight and obesity in the world. Around two thirds of us are now overweight or obese – and therefore at higher risk of developing a host of other related diseases, including arthritis, mental health problems and reproductive issues for women.

Overweight and obesity: how are they defined?

Body types vary considerably. One person’s healthy weight may be considered overweight in another person, depending on factors such as muscle and bone mass, ethnic origin and how much and what type of physical activity they do.

One of the most commonly-used international measures to try to standardise and define overweight and obesity in adults is the body mass index (BMI).

Your BMI is calculated by dividing your weight in kilograms by the square of your height in metres.

So if you weigh 65kg and you are 170cm(or 1.7m) tall, you calculate your BMI by:

  • Multiplying 1.7 by 1.7 = 2.89
  • Dividing 65 by 2.89 = 22.49, rounded up to get a BMI of 22.5

Having a BMI of:

  • 18.5 to under 25 indicates a healthy weight range
  • 25 or more indicates that you are overweight
  • 30 or more indicates that you are obese

The BMI applies only to adults. For children and adolescents, it can be more difficult to assess healthy weight because their height and body composition are continually changing.

Abdominal obesity and waist circumference

It’s now known that where in your body you carry excess weight also makes a difference to your heart disease and diabetes risk.

Carrying weight around your middle (having an ‘apple’ shape) rather than around the hips, thighs and buttocks (a ‘pear’ shape) increases your risk.

Therefore, another useful way to assess your weight-related risk of heart and other diseases is by measuring your waist circumference.

If you’re a woman with a waist circumference of:

  • 80cm or more – you’re at increased risk
  • 88cm or more – you’re at substantially-increased risk and are considered to be abdominally obese

If you’re a man with a waist circumference of:

  • 94cm or more – you’re at increased risk
  • 102cm or more – you’re at substantially-increased risk and are considered to be abdominally obese

Again, these figures apply to adults only, not children or adolescents.

Some ethnic groups such as Asians and Indians are at genetically-increased risks of heart conditions and type 2 diabetes at much lower BMIs and waist circumferences.

Causes of overweight and obesity

A range of factors can play a role in how much you weigh, including genetics and having certain medical conditions.

In the vast majority of cases, however, by far the greatest determinant of your weight is the simple matter of how much energy you consume in the form of food and drink compared to how much you expend in your everyday metabolism, activities and exercise.

If you continuously take in more energy than you expend, the result will be overweight or obesity. If you continuously expend more than you take in, the result will be weight loss. If you can achieve the fine balance between energy in and energy out, you will maintain a stable weight.

Next: Activity and exercise

Last published 31 October 2011

This information has been developed and reviewed for Bupa by health professionals. To the best of their knowledge it is current and based on reputable sources of medical research. It should be used as a guide only and should not be relied upon as a substitute for professional medical or other health professional advice.

Bupa Australia Pty Ltd makes no warranties or representations regarding the completeness or accuracy of the information. Bupa Australia is not liable for any loss or damage you suffer arising out of the use of or reliance on the information. Except that which cannot be excluded by law. We recommend that you consult your doctor or other qualified health professional if you have questions or concerns about your health. For more details on how we produce our health content, visit the About our health information page.

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