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9-minute read

Key facts

  • Obesity is defined as excessive body fat that increases your risk of health problems.
  • A person with obesity has a body mass index (BMI) over 30, while a person who is overweight has a BMI between 25 and 30.
  • Most people with obesity and people who are overweight take in more energy from food and drink than they use up with physical activity.
  • In most cases, a kilojoule-controlled diet and regular physical activity will help you to lose weight and feel healthier.
  • If you are struggling to lose weight with diet and exercise, speak to your doctor about other treatments that may help.

What is obesity?

Living with obesity or being overweight means that you are carrying too much weight in the form of body fat. Living with obesity puts you in the highest weight range, above what’s considered healthy. Being overweight also means your body weight is outside a healthy range, but it’s not as extreme as obesity.

In Australia, 2 out of 3 adults and 1 in 4 children are living with obesity or are overweight. Obesity is more common among disadvantaged Australians. Experts predict that by 2025, more than 3 in 4 Australian adults will be either overweight or living with obesity.

Obesity can be a sensitive topic. It’s important to remember that obesity is not just about appearance — it increases a person’s risk of heart disease, type 2 diabetes and other serious conditions.

What are the signs of obesity?

The most visible sign of obesity is excess body fat, usually measured by body mass index (BMI). A BMI of 30 or higher indicates obesity, while a BMI between 25 and 30 is considered overweight.

You can calculate your BMI using healthdirect’s BMI calculator for adults. However, standard BMI calculations may not be accurate for people under 18 years, pregnant women, and people from certain ethnic backgrounds. If you’re unsure, ask your doctor or dietitian if BMI applies to you.

BMI CALCULATOR — Use the BMI Calculator to find out if your weight and waist size are in a healthy range.

What causes obesity?

Many things can cause weight gain. For most people, obesity happens gradually by taking in more energy than your body needs over time. Foods and drinks contain energy (measured in kilojoules), which your body uses, especially during physical activity. The average adult needs 8700 kJ each day. Any extra energy you consume is stored as body fat.

Other things that can cause weight gain

Obesity can also happen because of factors outside of your control, such as:

  • your family history — the habits you grew up with and the genes you got from your parents
  • your surroundings — what kinds of food are available and in what portions, and where you work and sleep
  • your metabolism — how efficiently your body turns food into energy
  • certain medical conditions that cause weight gain — such as hypothyroidism
  • certain medicines that cause weight gain as a side effect — such as some antipsychotic medicines

Whatever the cause of your obesity, talk to your doctor about ways to improve your health.

What can I do to manage obesity?

Here are some steps that you can take to help reduce the likelihood of obesity:

  • Eat well: Review how much high-energy, low-nutrition snack foods and sugary drinks you have, including juice, soft drink and flavoured milk. Consider how often you get takeaway.
  • Do enough physical activity: Only half of Australians do enough physical activity for good health.
  • Limit alcohol: Review how much alcohol you drink — alcohol has many kilojoules with no nutritional benefits.

Stress, low mood, poor-quality sleep, changing emotions and poor access to healthy food can all cause people to take in more kilojoules than they need.

How is obesity diagnosed?

Body mass index

Your doctor will measure your height and weight to calculate your BMI and to assess whether you are living with obesity or overweight.

For most adults:

  • A BMI between 18.5 and 24.9 is considered healthy.
  • A BMI between 25 and 29.9 is considered overweight.
  • A BMI of 30 or higher is considered obesity.

A BMI measurement may be less accurate in certain groups of people who naturally have different muscle and fat mass. For example, athletes with high muscle mass may be considered as people with obesity based on their BMI, when they actually have a healthy weight. Children should not use a standard BMI measure. Read more on measuring and managing obesity in children.

Waist circumference

Your doctor may measure your waist circumference to assess your weight. Obesity-related health problems, such as type 2 diabetes, heart disease and some cancers, are more likely if you have a waist circumference of 94cm or more (for males) or 80cm or more (for females who aren’t pregnant).

Other tests

Your doctor may measure your blood pressure, blood glucose (sugar) and lipid (cholesterol) levels to assess your risk of other conditions associated with obesity.

How is obesity managed?

Unfortunately, there is no ‘quick fix’ or fast treatment for obesity. In most cases, a kilojoule-controlled diet with regular physical activity will help you to lose weight and feel better. Looking after your mental health and keeping a positive attitude also helps.

Reducing your kilojoule intake

One way to lose weight is to change your diet to create an energy deficit. You can do this by swapping unhealthy and high-energy food choices, such as fast food, processed food, sugary drinks and alcohol, for healthier choices such as vegetables and fruit. Be careful of diets that encourage unhealthy behaviours or restrict certain foods completely. If you are planning to change your diet, it may be helpful to speak with a dietitian about a food program tailored to your needs.

Increasing physical activity

To lose weight, it’s important to change your diet and do at least 30 minutes of moderate-intensity physical activity most days of the week. Anything that requires more effort than usual is considered physical activity, including brisk walking, swimming or playing tennis.

You can do many physical activities in your daily life. You can take the stairs instead of the lift, be active with your children, take public transport or cycle. You may find it helpful to join an exercise group or sports team for motivation and support.

Research shows that:

  • Doing any physical activity is better than doing none.
  • Doing daily physical activity is more effective than only once or twice a week.
  • Strength or resistance training exercise (exercising with weights) at least twice a week helps your metabolism (how fast you burn energy) and bone health.

Supporting your weight loss

If you’ve found it hard to lose weight in the past, it may be helpful to see a counsellor or psychologist who can help you with long-term changes. Techniques such as cognitive-behavioural therapy can help make it easier to lose weight by teaching you to recognise when and why you eat, or to change unhelpful thoughts or thinking patterns. Your doctor can refer you to a counsellor or psychologist.

Weight-loss medicines

Prescription medicines are available for weight loss in Australia. It's important to use these while you reduce your kilojoule intake and increase physical activity. Some medicines work by reducing the amount of fat you absorb from food; others make you feel less hungry. Weight-loss medicines have side effects and aren't suitable for everyone. Talk to your doctor or pharmacist before starting a weight-loss medicine to see if it's right for you.

Weight-loss surgery

Bariatric surgery can help some people lose weight by changing the way the body digests and absorbs food. When considering weight-loss surgery, your doctor will assess your BMI, whether you’ve tried other methods to lose weight and how much obesity affects your daily activities.

Complementary therapies and supplements

There are many alternative treatments and pills that are said to work for obesity and weight loss. They shouldn’t replace the proven methods described above. Speak with your doctor or pharmacist before taking complementary therapies or supplements that claim to help you lose weight.

Are there complications of obesity?

Being overweight or living with obesity is associated with several other health conditions. These include:

You doctor can assess whether you’re more likely to have health complications because of obesity.

ARE YOU AT RISK? — Are you at risk of type 2 diabetes, heart disease or kidney disease? Use the Risk Checker to find out.

Obesity, eating disorders and mental health

Some people with obesity have an eating disorder, which may make it more difficult to manage weight without extra support. Often, people who are overweight are not aware that they have an eating disorder. Read more on eating disorders for people with obesity.

You may find it helpful to speak with a mental health professional about your weight, particularly if your weight interferes with you working, being active or socialising.

When should I see my doctor?

See your doctor if you are overweight or living with obesity and want to lose weight.

You can discuss things including:

  • assessing your BMI, waist measurement and health risks regularly
  • how to improve your diet
  • how much and what type of exercise is appropriate for you
  • whether you need further tests or treatments for obesity-related conditions
  • a referral to a dietitian for professional guidance on what and how much to eat
  • a referral to a mental health professional if your weight is interfering with your sense of wellbeing

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

Resources and support

For more information and support, try these resources:

  • Call GetHealthy NSW on 1300 806 258 for free phone-based health coaching to help you reach your healthy lifestyle goals.
  • Dietitians Australia has nutrition information, tips and recipes to help you eat well.
  • LiveLighter offers a range of tools and calculators to help you make lifestyle changes to improve your health.

Where can I find information in other languages?

Do you prefer other languages than English? The Victorian Government's Health Translations has fact sheets on obesity in Arabic, Chinese, Tagalog and Vietnamese.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: September 2022

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