Does Your Child's BMI Matter?

The Body Mass Index scale --- the formula that assigns weight categories --- was developed by a Flemish statistician in 1835 who hoped it would help streamline health policy. The adult scale is calculated by dividing a person's weight in kilograms by the square of their height in meters. (It doesn't factor in age, gender, or muscle mass --- all of which impact our body composition and health.) For kids, doctors use a similar height and weight calculation and then plot that number as a percentile on a BMI-for-age chart, which shows how they're growing compared with same-sex peers.

The current chart classifies kids as overweight if they fall between the 85th and 94th percentiles and obese if they're at the 95th percentile or higher. Experts say the system often waves a red flag unnecessarily,

and that pediatricians should look at a child's growth history instead. "Science doesn't consistently show an increased risk for health problems until kids are at or above the 95th percentile. Before that, kids aren't necessarily at an unhealthy weight --- they're likely just growing," says Hannah Thompson, Ph.D., an epidemiologist at the University of California, Berkeley, who studies public-health interventions in schools. The chart is also based on what mostly white children weighted between 1963 and 1994 and doesn't reflect the diversity of kids today.The Body Mass Index scale --- the formula that assigns weight categories --- was developed by a Flemish statistician in 1835 who hoped it would help streamline health policy. The adult scale is calculated by dividing a person's weight in kilograms by the square of their height in meters. (It doesn't factor in age, gender, or muscle mass --- all of which impact our body composition and health.) For kids, doctors use a similar height and weight calculation and then plot that number as a percentile on a BMI-for-age chart, which shows how they're growing compared with same-sex peers.

The current chart classifies kids as overweight if they fall between the 85th and 94th percentiles and obese if they're at the 95th percentile or higher. Experts say the system often waves a red flag unnecessarily,

and that pediatricians should look at a child's growth history instead. "Science doesn't consistently show an increased risk for health problems until kids are at or above the 95th percentile. Before that, kids aren't necessarily at an unhealthy weight --- they're likely just growing," says Hannah Thompson, Ph.D., an epidemiologist at the University of California, Berkeley, who studies public-health interventions in schools. The chart is also based on what mostly white children weighted between 1963 and 1994 and doesn't reflect the diversity of kids today.