Scaling of body composition to height: Relevance to height-normalized indexes

Background: Body weight scales to height with a power of ≈2, thus forming the basis of body mass index (weight/height²). The corresponding scaling of body composition to height has not been established in a representative sample of US adults. Objective: The aim of the study was to examine the scaling of weight, fat, fat-free mass, and bone mineral content to height. Design: Adult non-Hispanic white (NHW), non-Hispanic black (NHB), and Mexican American National Health and Nutrition Examination Survey (NHANES) participants were included in allometric analyses if they had complete age, weight, height, and body-composition data as measured by dual-energy X-ray absorptiometry. Powers of height in allometric regression models were developed for each measure and adjusted for age. Results: The analyses included 13,183 subjects (6699 NHW, 3015 NHB, and 3469 Mexican American). The scaling of weight to height across sex-race groups provided powers (mean ± SE) ranging from 1.85 ± 0.12 in Mexican American women to 2.48 ± 0.17 in Mexican American men. Powers of height for body composition similarly ranged widely and were often outside the 95% CI for a power of 2. Of the 3 body-composition measures, the mean age-adjusted powers of height rounded to 2 as the nearest integer in 16 of 18 sex-race groups. Conclusions: Adult weight and body composition scale to height with variable age-adjusted powers that are sometimes outside the 95% CI for a power of 2 but frequently round to 2 as the nearest integer. These observations have implications for developing height-adjusted body-composition indexes.