Definition Of Overweight In Children

Overweight and obese are labels applied to children and teens whose weight is considered excessive relative to their height, age and gender. Technically, according to the National Institutes of Health, overweight refers to excessive weight that could result from muscles, bone, water or adipose tissue. Generally, however, most studies utilize a metric, the Body Mass Index (BMI), to distinguish children on the basis of weight relative to height. These studies assume that excessive weight is due to adipose (i.e., fat) tissue.

BMI Use

People commonly employ the BMI to determine if a child meets the definition of overweight or obese. BMI estimates the amount of body fat on a person. As noted at the Centers for Disease Control, while BMI is correlated with body fat, it does not directly measure body fat. Athletes who participate in rigorous physical conditioning may have significant muscle mass that contributes to weight, causing the BMI to overestimate their body fat. This may be an issue in measuring BMI in athletic adolescents but most likely does not significantly affect most estimations of BMI in children. Nonetheless, while the BMI serves as an acceptable screening tool to estimate body fat, it is not considered a diagnostic measure because it does not directly measure body fat.

BMI Standards

The most common standard used for defining children's weight status is the Centers for Disease Control (CDC) 2000 growth chart. This chart uses 2000 census data to establish norms for children's weight. Body composition varies as children age and varies for boys and girls, so weight classifications are assigned on the basis of children's gender and height. Generally, children place into the overweight category if their weight lies within the 85th to 94.9th percentile for their sex, age and height. Children who weigh in at or above the 95th percentile for their sex, age and height usually receive the designation of obese.

Limitations of Current Standards

Differing standards are proposed for defining overweight and obesity. Consequently, comparing results from different sources can be difficult. Experts established norms for defining overweight and obesity for adults on the basis of empirical research that linked health risks to particular weights, according to the British Medical Journal. In contrast, cutoffs for children are based on somewhat arbitrary statistical standards derived from particular reference populations, which may vary across different studies. While many studies use United States 2000 census data as a reference group, other sources, such as Medical News Today, utilize a different reference population.

Prevalence

Because of the different standards employed, different studies suggest different prevalence rates of overweight children. Some sources establish a BMI ranging from the 85th percentile to less than 95th percentile as overweight or as "at risk of being overweight," while other sources define being at or above the 95th percentile as overweight. Medical News Today examined data from 2003 to 2004 and found about 17 percent of children aged 2 to 19 to be overweight, defining overweight as at or above the 95th percentile of the age-growth charts obtained from 1963 through 1994. The Centers for Disease Control, using the 95th percentile as a cutoff, reports that from 2005 to 2006, 18 percent of 12- to 19-year-olds were overweight, 15 percent of 6- to 11-year-olds were overweight, and 11 percent of 2- to 5-year-olds were overweight. Other sources, such as Kids's Health, use a 85th percentile cutoff and report that as many as one in three children are overweight.

Assessing Your Child

If you have concerns that your child may be overweight, you can estimate her BMI score using an online calculator like the one at Keep Kids Healthy. Keep in mind that the online calculators do not directly measure body mass or body fat. They provide estimates based on a general formula and a particular normative reference group. Seek consultation from your child's pediatrician if you have continued concerns about your child's weight.