Body mass index tracks growth

80% of kids have “normal” weight-to-height ratios.

As a 10-pound newborn, my son got lots of attention from strangers for being an adorable baby with fat rolls from his thighs to his wrists. But if fat is a good thing in babyhood, it is decidedly unhealthy for a child.

Childhood obesity health concerns include high blood pressure, high cholesterol, sleep apnea, joint problems and even psychological problems caused by poor body image.

If obesity continues into adulthood, “the risks for disease are amplified,” says April Douglass-Bright, MD, head of the Division of General Pediatrics at Cooper University Hospital in Camden, NJ.

Body mass index

BMI Percentiles

Percentile Condition
0-4 Underweight
5-84  Normal
85-94 Overweight
95-100 Obese

Doctors see infants several times during their first year, when growth proportions are monitored using weight-to-height ratios. After age 2, body mass index (BMI) is used as a reliable indicator of body fat. BMI is calculated from a person’s weight and height. For adults, it is expressed as a number: 18 to 25 is the healthy range. For children, BMI is expressed as a percentile that compares the child to kids of the same age and gender. 

BMI percentiles give a very broad range for normal, and they allow for many different body shapes and sizes. “The extremes are really the issue,” says Dr. Douglass-Bright. “Children have a tendency to follow their growth percentile after the age of 3.” Before that age, the BMI percentile is not much of a predictor, but after that the child is likely to remain in roughly the same percentile into adulthood.

Beyond BMI

Figure this

Pediatric nutrition specialist Dr. Elizabeth Parks suggests memorizing the following number as a mnemonic for “optimizing children’s food and activity habits”:


5 fruits and vegetables a day

2 or fewer hours of screen time per day

1 hour of exercise a day

0 sugary drinks

In addition to BMI, doctors look at growth velocity, or rate of growth. They are hoping to see consistency. “The goal is not to change a whole lot but to stay on your curve,” says George Datto, MD, chief of the Division of Weight Management at A.I. duPont Hospital for Children in Wilmington, DE. “We need these (growth velocity) charts and measurements to give you an idea of when you’re getting away from normal growth,” he explains.

MetroKids Facebook fan Belinda Ritter recalls that her son used to be built like a twig. But her pediatrician recently told her that 9-year-old Cameron fell into the obese range on the BMI chart. As a result, his doctor recommended diet control and exercise. Ritter later explained to Cameron, who didn’t quite understand what obesity meant, “We’re making changes to your diet so you can be healthy.”  She continues to emphasize to him that it’s not about fat and weight. “It’s about health,” she says.

 “The big thing to remember is that BMI is a screening tool,” says Elizabeth Prout Parks, MD, a pediatric nutrition specialist at the Children’s Hospital of Philadelphia. BMI does not diagnose weight issues and it does not explain why they occur. It does help to find kids who are at risk for obesity-related diseases so that parents can work to change their habits.

Suzanne Koup-Larsen is a contributing writer to MetroKids.

Categories: Health