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Obesity in children

8-minute read

Key facts

  • Childhood obesity is when a child has too much body fat for their age.
  • Being overweight and living with obesity are common in Australia, affecting 1 in 4 Australian children.
  • Children living with obesity generally have a body mass index (BMI) at the 95th percentile or higher for their age group.
  • Helping a child or teenager maintain a healthy weight means they’re less likely to struggle with weight problems as adults.
  • You can help manage obesity in children by modelling healthy eating habits with them, encouraging lots of physical activity and limiting screen time.

What is obesity in children?

A child or adolescent who is living with obesity has more body fat than other children of the same age. If your child is living with obesity, they will be in the highest weight range, outside what’s considered healthy for their age. If your child is overweight, their body mass is also outside a healthy range, but not as much as a child with obesity.

In Australia, around 1 in 4 children aged between 4 and 15 years live with obesity or are overweight.

What are the signs of obesity in children?

The most visible sign of obesity is excess body fat, but it’s not always easy to tell if your child is living with obesity or overweight.

Your child is healthiest if they stay within a certain weight range for their age known as a ‘BMI-for-age’. A BMI-for-age score between the 85th and 95th percentile may mean that your child is overweight. A score at the 95th percentile or higher may indicate they are living with obesity.

You can use NSW Health’s healthy weight calculator to estimate your child’s BMI-for-age. Remember that most online BMI calculators are designed for people aged 18 years and over. It’s best to see your doctor to understand your child’s BMI measurements as they grow.

What causes obesity in children?

Many things can cause weight gain. For most children, obesity happens because they gradually take in more energy (measured in kilojoules) from eating and drinking than the amount their bodies use to grow, play and exercise. Unused energy is turned into body fat, which over time may increase your child’s body weight beyond what’s healthy for their age.

Other causes of obesity in children

Some causes of obesity and excessive weight gain may be outside your control, such as the way their body works (for example, your child’s metabolic rate — how quickly their body uses energy), their lifestyle and their environment.

Your doctor can also help look out for and address:

How can I help my child to maintain a healthy weight?

Here are some steps that families can take to help their child maintain a healthy weight:

  • Eat well: Review how much high-energy, low-nutrition snack foods and sugary drinks your family has, including juices, soft drinks and flavoured milk. Consider how often you get takeaway.
  • Do enough physical activity: Only 1 in 4 children aged 5 to 12 years do enough physical activity each week.
  • Limit screen time: 2 out of 3 children aged 5 to 12 years spend more than the recommended maximum of 2 hours a day in front of screens such as computers, televisions, smartphones and tablets.

How is obesity in children diagnosed?

Body mass index

Your doctor will use a BMI percentile chart to assess whether your child or teenager’s weight is healthy for their age. BMI is calculated as the ratio of weight in kilograms divided by height in metres squared (kg/m2). For children, this is charted across weight information for the whole population as a growth curve.

A healthy BMI for children and teenagers will vary according to their age:

  • A BMI-for-age between the 5th and 85th percentile is considered a healthy weight.
  • A BMI-for-age between the 85th and 95th percentile is considered overweight.
  • A BMI-for-age at the 95th percentile or greater is considered obesity.

Because a healthy BMI depends on your child’s age and sex, it’s best to seek professional advice on how to interpret your child’s BMI results.

Waist circumference

Sometimes your doctor may want to measure your child’s waist circumference. This is done using a measuring tape around your child's stomach, at roughly their belly button, and taking their measurement while they breathe out.

How can I support my child with obesity?

It’s much easier for children with obesity to achieve a healthy weight when their family supports them.

For young children in particular, focus on maintaining a healthy weight rather than weight loss. Help them 'grow into their weight', rather than going on a diet that may cut important nutrients while they’re still growing.

Share healthy eating habits

Kids who grow up with healthy eating habits are more likely to make healthy food and drink choices when they’re older.

Here are some suggestions to encourage your child to eat healthily:

  • Eat a wide variety of vegetables, fruits, grains, proteins and reduced-fat dairy foods each day.
  • Cut back on junk foods that contain extra salt, sugar and saturated fat, such as biscuits, cakes, lollies, chips and fast food.
  • Drink water instead of sugary drinks such as soft drinks and fruit juice.
  • Encourage your children to eat only when they are hungry, and to stop when they're full, rather than asking them to finish what’s on their plate.
  • Explain to your child that some foods are 'sometimes' foods. Save them for special occasions.
  • Make mealtimes free from screens and eat meals as a family.

See more ideas on healthy eating habits to share with your child.

Get active together

Physical activity is an important way to achieve and maintain a healthy weight. School-aged children need at least 60 minutes of activity every day.

You can encourage your children to be active by doing physical activity together. Here are some ideas:

  • Set an example and be active yourself.
  • Include physical activity in your and your family’s day, such as walking to school and doing household chores together.
  • Make the most of your local bush track, bike path, playground or sports field.
  • Sign your child up to play a team sport.
  • Limit screen-based activities to 2 hours a day for school-aged children, and less than 1 hour a day for preschoolers and toddlers.

How can I talk to my child about obesity?

How you talk to your child about obesity can affect their willingness to keep a healthy weight.

Keep the focus of your conversation on maintaining a healthy lifestyle and good health. You can consider the following tips:

  • Instead of talking about being 'fat', 'heavy' and 'obese', use phrases like 'above your healthiest weight'.
  • Don’t compare your child to their peers. Discourage them from comparing themselves.
  • Instead of labelling foods or activities as 'good' or 'bad', use words like 'healthy' and 'healthier options'.
  • Don’t make negative comments about your own weight or body shape as your children will notice these.
  • Focus on steps towards a healthy lifestyle rather than setting weight-loss goals.

When should I take my child to see a doctor?

Healthcare professionals can help you support your child to achieve a healthy weight. If you have questions, or if the changes you've made don't seem to be helping, see your doctor and check in with them regularly.

Your doctor can assess your child's weight and advise on lifestyle changes or refer you to other health professionals such as a paediatrician, dietitian or psychologist.

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What are the complications of obesity in children?

If left unchecked, obesity can cause physical, social and emotional health problems.

Weight-related complications include:

The longer your child has an unhealthy body weight for their age, the more likely it is that your child will live with obesity as an adult, which carries its own health risks.

Resources and support

For more information and support, try these resources:

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Last reviewed: September 2022

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