Objective: To compare the body mass index (BMI) (weight/height2) and the Ponderal index (PI) (weight/height3) in childhood as predictors of adult overweight in a biracial group of children.
Design: Prospective, 15-y follow-up.
Subjects: 835 children aged 10-15 y at baseline.
Measurements: Weight in kg and height in m.
Outcome variable: Overweight, defined as a BMI greater than 27 kg/m2 in young adults.
Results: Overall, the BMI and the PI at baseline were identically correlated with the BMI at follow-up (r = 0.64, p < 0.001). However, the predictions of overweight based on each index were distinctively affected by age, sex and race. The probability of adult overweight among 10-year old children was greater than 0.5 (50% overweight threshold) if their BMI exceeded 17 kg/m2 in black girls, 20 in white girls and 18 in boys of either race. Similarly, the 50% BMI overweight thresholds among 15-year-old children were 23 kg/m2 for black girls, 25 for white girls and 22 for boys of either race. The 50% PI overweight thresholds (in kg/m2) were 12 and 14 for 10-year-old black girls and white girls, respectively; and 14 and 16 for 15-year-old black girls and white girls, respectively. Among boys, the 50% PI threshold was 13 kg/m3 regardless of age or race.
Conclusion: The BMI and the PI in childhood were both useful in assessing sex-and race-specific risks of adult overweight. However, assessments based on the Ponderal index were less affected by age and race than those based on the BMI, particularly among boys. Hence, to establish general weight goals for children, aimed at preventing adult obesity, the PI could be a much better choice than the BMI.