Health conditions

Overweight and obesity in adults

Overweight and obesity are terms used to describe ranges of weight that have been shown to increase a person’s risk of certain conditions and health problems.

Body Mass Index (BMI) is a useful measure of overweight and obesity for adults. It is calculated from a person’s height and weight.

BMI Classification
Below 18.5
Underweight
18.5 – 24.9
Healthy weight range
25.0 – 29.9
Overweight 
30 and above
Obese

While BMI provides a good estimate of body fat for most people, it may not be suitable for some groups such as athletes who have a muscular build, older people and some ethnic groups.

Waist circumference is another good indicator of total body fat and can be a better predictor of health risk than BMI.

For tips on how calculate your BMI and measure your waist circumference, see assessing your weight.

Impact on health

Being overweight or obese can increase the risk of physical and mental health problems such as:

Causes of overweight and obesity

The main cause of overweight and obesity is energy imbalance. Over time, if people eat and drink more than the body needs and uses in day-to-day activities, this extra energy will be stored as fat.

Many factors have contributed to the increasing rates of overweight and obesity, including: 

  • Food choices – choosing foods that are high in fat, sugar and/or salt that provide little nutrition and more energy than the body needs (such as cakes, biscuits, confectionary, chocolate, pastries, pies, potato chips, soft drinks, cordials, sports and energy drinks and alcoholic drinks).
  • An inactive lifestyle – many Western Australians are not physically active enough for good health and spend too much time sitting.
  • Genes – genetic factors may increase a person’s risk of being overweight or obese. Though genes alone do not explain the increase in population rates of overweight and obesity.
  • The (obesity promoting) environment the modern environment is one that makes it harder for people to be active enough and make healthy food choices:
    • Changes to the food supply have led to increased availability and promotion of cheap, processed foods which are high in energy and low in nutrients.
    • The portion size of many packaged foods and foods prepared outside the home has increased. The cost of these foods has also decreased when compared to healthier options.
    • More people now have desk jobs where they sit for most of the day.
    • Where people would once walk or cycle to get to places, many now travel by car.
    • More convenient lifestyles and devices like elevators and remote controls mean we use less energy.
    • Sedentary entertainment and recreation options such as watching the television and using the computer and other electronic devices rather than getting out and being active.
  • Early life experiences –poor nutrition, smoking and gaining more than the recommended levels of weight during pregnancy can increase a child’s risk of becoming obese later in life. Evidence also shows that breastfeeding for at least six months reduces the risk of obesity in childhood, adolescence and early adulthood.

How to manage overweight and obesity

If a person is overweight or obese, even small amounts of weight loss (5% of body weight, for example, 5kg for someone who weighs 100kg) can bring a range of health benefits such as improved blood pressure, cholesterol and blood sugar levels.

Healthy weight loss is not about a ‘diet’. It’s about making changes to your lifestyle by adopting healthy eating patterns and having a more active lifestyle (and sitting less). You are more likely to be successful at keeping the weight off when the changes you make to your lifestyle are healthy, realistic and sustainable.

Making changes to your diet and physical activity can also have health benefits that are independent of weight loss, including increased energy, better sleep and reduced risk of depression. 

For healthy weight loss tips visit healthy weight loss for adults.

Where to get help

Remember

  • Overweight and obesity can increase a person’s risk of a range of conditions and health problems.
  • There are many factors that have contributed to population increases in overweight and obesity.
  • If a person is overweight or obese, even small amounts of weight loss can have a range of health benefits.

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

Infographic: Pants don't fit like they used to? know your ideal weight