Health & Well-Being-BMI not enough to screen kids
Health & Well-Being-BMI not enough to screen kids
An explosion of "super-sized" kids may have U.S. health professionals clamoring for improved obesity screening tools. However, according to preliminary findings from a large-scale study, the body mass index (BMI) tool can produce inaccurate results if factors such as age, sex, maturity level, ethnic background, and physical activity are not considered.
"One out of six children in our study who had a BMI in the normal range had an unhealthy
level of body fat," notes Kenneth Ellis, MD. Ellis is a professor of pediatrics at Baylor College of Medicine in Houston who studies growth and body composition
at the USDA/ARS Children's Nutrition Research Center, also
in Houston. "And one out of four with a BMI in the at-risk-to-obese range had a body fat level that was normal."
The study compared the results of two obesity indexes, the BMI and the percent body fat, in an ethnically diverse population of 979 boys and girls between the ages of three and 18.
Two basic assumptions regarding body composition lead to inaccuracies when the BMI is used as a one-size-fits-all screening tool for fatness, says Ellis. One assumption is that individuals who have a BMI within the normal range have
an average amount of body fat. The other is that every ounce of body weight over the standard weight for height is fat.
These assumptions generate the most classification errors for children with BMI values in the gray area between normal weight and overweight, which is a BMI between 18 and 20 for most ages, says Ellis.
Few people think that normal-weight kids can have too much body fat. "If we rely on BMI alone, we risk allowing kids who probably need some type of intervention to improve their physical activity and eating habits fall through the cracks," Ellis warns.
Of equal concern is the risk of mislabeling 25% of high-BMI children as at risk or overweight, despite their normal body fat percentage.
"Children are very sensitive to labeling," Ellis says, noting that high levels of physical activity, early maturation, genetics, and ethnicity can all contribute to a child having a high BMI but a healthy amount of body fat.
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