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Is Your Child Fat?
January 03, 2005
Rebecca Goldin
The definition of “overweight” is hard to come by.

Having had its fill of scare stories about overweight adults, the media has turned its attention to the “youngest victims” of the “obesity epidemic.” There’s little doubt that American children, like adults, are getting heavier. However, being “overweight” as a child has traditionally been defined in comparison to the weight of others the same age. When the whole population of kids gains weight, then, it becomes hard to know how bad the situation really is.

Countless news stories have focused on the reasons for this problem (television and bad eating are widely blamed), and how to begin to fix it (exercise and better eating). The most recent National Heath and Nutritional Examination Survey (NHANES) found that more than 10 percent of children age 2-5 are overweight, as are millions of older children.

In certain pockets of the U.S., according to these accounts, the situation is even worse. The Philadelphia Inquirer reported that 51 percent of children in Philadelphia are overweight and 43 percent of all children in five counties in Southeastern Pennsylvania. A New Jersey state Health Department survey found 38 percent of sixth-graders were overweight. The New York Times Magazine found that “[in] elementary school, 50 percent of the boys are overweight or obese, along with 35 percent of the girls” in Starr County, Texas.

But what exactly is overweight or obesity for a child?

The media has been coy on these critical facts, all the while insisting that parents get involved in solving the problem. The Boston Globe asserted that “doctors and parents need to watch the weight of even very young children.” Experts cited “the prevalence of junk food marketed to children, too much TV and the decline in the number of families who sat down together to eat” as the cause, according to the Globe. Yet without a working definition, it may be difficult for people to determine whether a child is overweight, or just outgrowing his or her baby fat.

For adults, overweight is by definition a body mass index (BMI) higher than 25. The BMI is defined by weight (in kg) divided by height squared (in square meters).

But according to the Centers for Disease Control (CDC) and the American Heart Association, the definition of an overweight child or teen aged 2-20 is relative.

A child is considered overweight if he or she has a higher BMI than 95 percent of other children the same age. There is no official definition of obesity using the BMI alone for children. Children and teenagers whose BMI is in the 85th to 95th percentile are considered “at risk for overweight.”

But if this is the real definition, then exactly 5 percent of children are overweight, no matter what their BMI actually is, since overweight then means being in the 95th percentile or above. Using this definition, one cannot assert that “more than ten percent of children ages 2-5 are overweight,” as did the Associated Press, based on the NHANES findings and published by the American Heart Association. The CDC and the American Heart Association should clarify the meaning of overweight, and stop using a percentile as a measure. It confuses the public because it suggests that overweight is only diagnosed when it is relative to the rest of the population and can falsely reassure people when the entire population has gained weight.

What researchers are actually using to devise the percentages cited in the stories is a comparison between today’s children and those whose BMI was in the 95th percentile of for children thirty-five to forty years ago. The charts used for measuring overweight were determined by the second National Health Examination Surveys NHES II, 1963-1965 for children ages 6-11. The charts for adolescents ages 12-17 were specified by NHES III, 1966-1970. An overweight child today would have been in the top 5 percent of kids two generations ago, measured in BMI.

Of all the major media organizations covering the story recently, only the Philadelphia Inquirer correctly instructed how to determine if a child is overweight.

"First calculate the body mass index, or BMI: Divide the child's weight in pounds by the square of the child's height in inches, and multiply by 703. You can also use a calculator found at [the CDC].

For an adult, this is where the calculating would stop. A BMI of 25 or above signifies being overweight. Thirty or above is considered obese.

Because children's growth varies with age and sex, their BMI must be plotted on a growth chart. The charts can be found at [the CDC]."

This information should be included in more of the coverage—so that parents can determine for themselves where their children stand.