28245098

PMC5373980

Objective

Although the CDC growth charts are widely used, BMIz is known to be uninformative above the 97th percentile. We compared the relations of BMIz and other BMI metrics (%BMIp95, percent of 95th percentile, and ΔBMIp95, BMI minus 95th percentile) to circumferences, skinfolds and fat mass. We were particularly interested in the differences among children with severe obesity (%BMIp95 ≥ 120).

Methods

We used data from 30,003 2- to 19-year-olds who were examined from 1999-2000 through 2013-14 in NHANES.

Results

The theoretical maximum BMIz based on the growth charts varied by more than 3-fold across ages. The BMI metrics were strongly intercorrelated, but BMIz was less strongly related to the adiposity measures than were ΔBMIp95 and %BMIp95. Among children with severe obesity, circumferences and triceps skinfold showed almost no association with BMIz (r ≤ 0.10), whereas associations with %BMIp95 and ΔBMIp95 ranged from r=0.32 to 0.79. Corresponding associations with fat mass ÷ height2 ranged from r=0.40 (BMIz) to r=0.82 (%BMIp95) among 8- to 19-year-olds.

Conclusions

Among children with severe obesity, BMIz is only weakly associated with other measures of body fatness. Very high BMIs should be expressed relative to the CDC 95th percentile, particularly in studies that evaluate obesity interventions.

CDC Public Access

CC999999/Intramural CDC HHS/United States
K24 DK105989/DK/NIDDK NIH HHS/United States
U18 DP003370/DP/NCCDPHP CDC HHS/United States