Childhood Obesity

Childhood obesity is a worldwide problem. At least 20 million children under the age of 5 years were overweight globally in 2005, based on World Health Organization statistics. According to the American Academy of Pediatrics (AAP), the percentage of overweight children in the United States is growing at an alarming rate, with one out of three kids now considered overweight or obese. It is important for parents to understand how to recognize if their child has a weight problem so they can effectively address the situation as soon as possible.
What is Obesity?
Obesity is an excess percentage of body weight due to fat that puts children at risk for many health problems. Obese children are:

  • More likely to have risk factors for cardiovascular disease, such as high cholesterol or high blood pressure.
  • At greater risk for bone and joint problems, sleep apnea, and social and psychological problems such as poor self-esteem.
  • More likely to become overweight or obese adults, which increases the risk for associated adult health problems, including heart disease, type 2 diabetes, stroke, several types of cancer, and osteoarthritis.

How is Obesity Measured?
In children older than two, obesity is measured by the Body Mass Index (BMI), which uses height and weight to estimate the amount of body fat. BMI is the most widely accepted method used to screen for overweight and obese children since it is inexpensive and easy to perform.

*Your child’s pediatrician should assess BMI at each well visit beginning at age two. 

Calculating BMI
To calculate BMI, divide weight in kilograms by height in meters squared; for pounds and inches, divide weight by height squared; and multiply the result by the conversion factor 703.

Simple-to-use BMI calculators are also widely available to easily figure out one’s BMI. The for Disease Control and Prevention’s (CDC) calculator can be found at

BMI Percentile
For children over two, BMI is age- and sex-specific because children’s body composition varies as they age and varies between boys and girls. After BMI is calculated, it is plotted on the CDC BMI-for-age growth charts to obtain a percentile ranking. Percentiles are the most commonly used indicator to assess the size and growth patterns of children. The percentile compares a child’s BMI to other children of the same sex and age.

[Insert Boy and Girl BMI charts]

The following table shows how to determine if a child is overweight or obese based on BMI.

Weight Status Category

Less than the 5th percentile
 Healthy weight
5th percentile to less than the 85th percentile
85th to less than the 95th percentile
Equal to or greater than the 95th percentile

How BMI is Used
BMI is used as a screening tool to identify possible weight problems for children. However, it is not a diagnostic tool since it is not a direct measure of body fat. This means that a child may have a high BMI for age and sex, but to determine if excess fat is a problem, a doctor would need to perform further assessments. Such tests may include skinfold thickness measurements, evaluation of diet and physical activity, and a review of family history. Fortunately, healthy lifestyle habits, including exercise and better food choices, can lower the risk of becoming overweight or obese.