Premium
BMI z ‐Scores are a poor indicator of adiposity among 2‐ to 19‐year‐olds with very high BMIs, NHANES 1999‐2000 to 2013‐2014
Author(s) -
Freedman David S.,
Butte Nancy F.,
Taveras Elsie M.,
Lundeen Elizabeth A.,
Blanck Heidi M.,
Goodman Alyson B.,
Ogden Cynthia L.
Publication year - 2017
Publication title -
obesity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.438
H-Index - 199
eISSN - 1930-739X
pISSN - 1930-7381
DOI - 10.1002/oby.21782
Subject(s) - percentile , national health and nutrition examination survey , body mass index , medicine , obesity , overweight , demography , gerontology , environmental health , population , mathematics , statistics , sociology
Objective Although the Centers for Disease Control and Prevention (CDC) growth charts are widely used, BMI‐for‐age z ‐Scores (BMIz) are known to be uninformative above the 97th percentile. This study compared the relations of BMIz and other BMI metrics (%BMI p95 , percent of 95th percentile, and ΔBMI p95 , BMI minus 95th percentile) to circumferences, skinfolds, and fat mass. We were particularly interested in the differences among children with severe obesity (%BMI p95 ≥ 120). Methods Data was used from 30,003 2‐ to 19‐year‐olds who were examined from 1999‐2000 through 2013‐2014 in the National Health and Nutrition Examination Survey (NHANES). Results The theoretical maximum BMIz based on the growth charts varied by more than threefold across ages. The BMI metrics were strongly intercorrelated, but BMIz was less strongly related to the adiposity measures than were ΔBMI p95 and %BMI p95 . Among children with severe obesity, circumferences and triceps skinfold showed almost no association with BMIz ( r ≤ 0.10), whereas associations with %BMI p95 and ΔBMI p95 ranged from r = 0.32 to 0.79. Corresponding associations with fat mass ÷ height 2 ranged from r = 0.40 (BMIz) to r =0.82 (%BMI p95 ) 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.