We all know that far too many kids weigh more than they should for optimal health and well being. But despite the dramatic surge in childhood obesity rates over the last three decades, there's evidence that the levels of obesity as measured by body mass index (BMI) are starting to steady—and, in some cases, drop. In fact, national survey data shows that the rate of obesity in two- to five-year-olds decreased from an estimated 13.9% in 2003-2004 to 8.4% in 2011-2012.
Despite the glimmer of hope, a new article published in Pediatric Obesity suggests that BMI—a popular, easy to use screening tool based on height and weight—falls short in identifying children with higher than desirable body fat levels. Although the Centers for Disease Control and Prevention (CDC) describes BMI as "a reasonable indicator of body fatness for most children and teens," a review of 37 studies of 53,521 four- to 18-year-olds found that 27% of children who were not classified (using BMI) as obese* had excess body fat levels.
According to Francisco Lopez-Jimenez, MD, Director of Preventive Cardiology at Mayo Clinic and senior author of the article, "BMI is based on body weight, not body composition (the amount of muscle and fat), and weight cannot discriminate muscle from fat." He adds, "A child's body weight can still be within "normal limits" even if he or she doesn't have much muscle mass but has a high level of body fat."
Although he considers BMI a good measure to capture population trends, David Katz, MD, Director, Yale University Prevention Research Center and Editor-in-Chief of the journal Childhood Obesity, says, "There are far more important metrics (than BMI) at the individual level—some requiring no technology other than our eyes." While Katz acknowledges that we may not like to talk about the difference between 'flab' and muscle, he says we know it when we see it. "An excess of fat tissue, or flab, is potentially harmful even at lower BMIs."
According to Lopez-Jimenez, an alternative to using BMI in children is to check waist and hip circumferences. He says, "If the waist it larger than the hip, the child likely has central obesity—unhealthy fat in the central portion of the body." Lopez-Jimenez also notes an old teaching that may be useful: "If you cannot see the ribs of your child when he or she raises his or her arms, there's probably a lot of fat under the skin."
Although Katz says that BMI can be a useful (albeit imperfect) gauge of body weight, having good muscle tone and being fit can be protective even in children with a high BMI. Because health matters far more than body weight, Katz recommends that parents and clinicians assess children's overall health with measures such as fitness, vitality, and energy level. While both Katz and Lopez-Jimenez recommend a nutritious diet and active lifestyle to help kids achieve and maintain a healthy body weight and optimize overall health, Lopez-Jimenez adds, "It is hard for a healthy child to become obese if he or she eats well and is constantly active."
*Obesity is defined as a BMI at or above the 95th percentile of the sex-specific CDC BMI-for-age growth charts.
Image of happy kids via shutterstock.