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Fact Sheet: Child Obesity

Obesity in Children

What causes a child to be obese?
For a child, the risk of becoming obese is determined by both genetic and environmental factors. As with adults, some children are genetically more susceptible to weight gain. The environment in which we live is also conducive to weight gain; for example, low social class, single parent families, single child families, excessive periods of inactivity.

The society we live in is fast paced, putting increasing demands and pressure on families. As a result fast food has become a very important and convenient source of food for families on the go.

Parents influence what their children eat as they are responsible for the food purchased and bought into the home. Parents also set examples for children by choosing to eat and drink particular foods, like many learnt behaviours, children will mimic their parents eating habits.

How is obesity measured in children?
As with adults, a BMI (Body Mass Index) number is calculated, dividing the child's weight in kilograms by their height in metres squared.

Weight kg    =   BMI
 Height x Height

BMI alone does not determine whether a child is overweight or obese.

For children and teens, BMI is age and sex-specific and is often referred to as BMI-for-age. Age and sex are important factors when calculating a child's BMI for two reasons:

  • The amount of body fat changes with age
  • The amount of body fat differs between girls and boys

Healthy weight ranges for children and teens are difficult to determine as:

  • Healthy weight ranges change with each month and for each sex
  • Height increases also change healthy weight ranges

By plotting an individual BMI value on a BMI chart (either girls or boys) we can obtain a percentile ranking. This percentile ranking indicates the relative position of the child's BMI among children of the same sex and gender.

BMI percentiles indicate the following:

  • BMI-for-age less than the 5th percentile indicates - underweight
  • BMI-for-age from the 5th percentile to less than the 85th percentile indicates - healthy weight
  • BMI-for-age from the 85th to less than the 95th percentile indicates - at risk of being overweight
  • BMI-for-age greater than the 95th percentile indicates the child is overweight

For example: John is a ten-year-old boy with a BMI of 18, this places him in the 75th percentile on the BMI chart; compared to another child his age, 75% have a lower BMI than he does. Placing in the 5th to 85th percentile, means John has a 'healthy weight' for his age, height and sex.

To calculate your child's BMI percentile ranking, log onto:

If you are concerned about your child's weight speak to your doctor. Do not diet a child without the assistance and/or supervision of your doctor and a New Zealand registered dietitian.

What are the risks of being an obese child?
As the number of overweight and obese children increases, medical complications associated with obesity, usually seen only in adults have now begun to appear in children and teenagers.

These complications include:

  • Heart related problems such as high blood pressure and high cholesterol
  • Type 2 Diabetes
  • Psychological effects, such as depression and low self-esteem
  • Respiratory problems such as asthma and sleep apnoea
  • Certain bone and hip conditions

Also, overweight children are at greater risk of becoming overweight or obese adults. Obese adults have on average have a reduced life expectancy of between 7 and 11 years.

What can be done?
Putting children on diets to reduce weight is not recommended. Children who are overweight should be allowed to grow into their ideal weight for height. However increasing numbers of obese children are being placed on diets to control their ballooning weight.

Children need to:

  • Eat many different foods
  • Eat enough for activity and growth
  • Eat mini-meals or snacks
  • Have plenty to drink
  • Have treat foods now and then
  • Take part in regular physical activity
  • Moderate the amount of time spent playing computer games and watching television

It is important for a child to see that the entire family is actively involved in any changes to existing eating patterns. Regular physical activity should also be the primary goal of the entire family.

Eating patterns should be flexible. If they are too strict, adherence will be low.

The Facts

Healthy habits are established in childhood. Healthy children are more likely to grow into healthy adults.

Parents make lifestyle choices for their children and habits are formed within family and whänua units. Social, economic and environmental forces all influence our food choices.

In New Zealand it is estimated that at least a third of all children lack sufficient economic and social resources to allow the minimum adequate standard of living and participation in society.

Findings from the 2002 National Children's Nutrition Survey indicate:

  1. Overweight and obesity in New Zealand children aged 5-14 years is at 31%. The rate in Pacific children stands at 62%; Maori at 41%; and other New Zealand children at 24%.
  2. On average 86% of females and 79% of males eat breakfast before they leave home in the morning for school. These figures are lower for Maori and Pacific children. 
  3. 22% of all children reported that their household could not always afford to eat properly.
  4. About 2 out of 5 children eat the recommended number of servings (at least two) of fruit everyday day.
  5. About 3 out of 5 children eat the recommended number of servings (3+ per day) of vegetables each day.
  6. A child with a high level of obesity is 60-70% more likely to become an obese adult. The likelihood of adult obesity also increases with the age of the child. Children who are obese between the ages of 2-8 years are less likely to become obese as adults, children who are obese between the ages of 10 and 18 are more likely to continue to be obese as adults.
  7. In an Auckland based study (conducted over four years by a team from Starship Children's Hospital lead by paediatrician Cameron Grant) found that one in every 10 Auckland children is growing up with vitamin deficiencies commonly found in the Third World.

For further information log onto: or to check BMI and Weight for age.