According to the federal Let’s Move! initiative, one in three children today is overweight or obese. That rate is 300% higher than it was in the 1980s. The body mass index (BMI) is a reliable assessment of body fat for children and adults alike. Current pediatric standards include measuring a child for BMI at age 2 or older, when the path to obesity may be already well established. A recent study identifies ways to assess BMI during infancy, when interventions may be more effective.

Shana E. McCormack and Sani M. Roy, both pediatric endocrinologists at The Children’s Hospital of Philadelphia (CHOP), led the study to see if BMI assessment during infancy served as a useful predictor of obesity at age 4. The researchers analyzed electronic medical records from the “Genetic Causes for Complex Pediatric Disorders” study, which was conducted by the Center for Applied Genomics at CHOP.

Of the 2,114 children in the McCormack-Roy study, all were healthy children from the Philadelphia area who had been born at full term. Each child had his or her BMI measured six or more times by age 13.5 months. The research team evaluated six clinical characteristics in addition to BMI:

  • Birth weight
  • Gestational age
  • Gender
  • Race / Population ancestry
  • Insurance type (Medicaid or non-Medicaid)
  • ZIP code

To assess the influence of population ancestry, the parents of the children in the study described their child as either African-American, white, or other/unknown. Sixty-one percent of the children were self-reported as African-American, a demographic known to have high rates of obesity and diabetes as adults. Most of the remaining children were of European ancestry.

A child’s BMI changes considerably during the first year of life, with BMI expected to peak between months eight and nine as the baby gains weight. As it gains more height than weight after about nine months, the child’s BMI lowers and then stabilizes at about age 4 years.

The research team discovered:

  • BMI peaked approximately 12 days earlier in African-American infants than the other infants.
  • Peak BMI magnitude was approximately 3 times higher in the African-American infants than the others.
  • The risk for obesity at age 4 was more than twice as high for African-American children as it was for children of European descent.
  • Peak infant BMI was a more significant indicator of childhood obesity than ancestry.
  • Children born into low socioeconomic households (as determined by insurance type and ZIP code) were more likely to reach peak infant BMI earlier and higher than other children.

Childhood obesity is strongly associated with obesity in adulthood, when excess weight triggers early onset of dangerous chronic conditions such as diabetes, hypertension, and cardiovascular disease. People who maintain a healthy weight from childhood to adulthood are more likely to live healthier, longer lives.


  1. Roy, Sani M., et al. "Body Mass Index (BMI) Trajectories in Infancy Differ by Population Ancestry and May Presage Disparities in Early Childhood Obesity (.pdf)." The Journal of Clinical Endocrinology and Metabolism. Endocrine Society, 30 Jan. 2015. Web. 18 Mar. 2015.