Explaining Discrepancies Between Total and Segmental DXA and BIA Body Composition Estimates Using Bayesian Regression.

ABSTRACT

INTRODUCTION/BACKGROUND: Few investigations have sought to explain discrepancies between dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) body composition estimates. The purpose of this analysis was to explore physiological and anthropometric predictors of discrepancies between DXA and BIA total and segmental body composition estimates. METHODOLOGY: Assessments via DXA (GE Lunar Prodigy) and single-frequency BIA (RJL Systems Quantum V) were performed in 179 adults (103 F, 76 M, age 33.6 ± 15.3 yr; BMI 24.9 ± 4.3 kg/m2). Potential predictor variables for differences between DXA and BIA total and segmental fat mass (FM) and lean soft tissue (LST) estimates were obtained from demographics and laboratory techniques, including DXA, BIA, bioimpedance spectroscopy, air displacement plethysmography, and 3-dimensional optical scanning. To determine meaningful predictors, Bayesian robust regression models were fit using a t-distribution and regularized hierarchical shrinkage "horseshoe" prior. Standardized model coefficients (ß) were generated, and leave-one-out cross validation was used to assess model predictive performance. RESULTS: LST hydration (i.e., total body waterLST) was a predictor of discrepancies in all FM and LST variables (|ß| 0.20-0.82). Additionally, extracellular fluid percentage was a predictor for nearly all outcomes (|ß| 0.19-0.40). Height influenced the agreement between whole-body estimates (|ß| 0.74-0.77), while the mass, length, and composition of body segments were predictors for segmental LST estimates (|ß| 0.23-3.04). Predictors of segmental FM errors were less consistent. Select sex-, race-, or age-based differences between methods were observed. The accuracy of whole-body models was superior to segmental models (leave-one-out cross-validation-adjusted R2 of 0.83-0.85 for FMTOTAL and LSTTOTAL vs. 0.20-0.76 for segmental estimates). For segmental models, predictive performance decreased in the order of appendicular lean soft tissue, LSTLEGS, LSTTRUNK and FMLEGS, FMARMS, FMTRUNK, and LSTARMS. CONCLUSIONS: These findings indicate the importance of LST hydration, extracellular fluid content, and height for explaining discrepancies between DXA and BIA body composition estimates. These general findings and quantitative interpretation based on the presented data allow for a better understanding of sources of error between 2 popular segmental body composition techniques and facilitate interpretation of estimates from these technologies.