A comparison of body fat percentage estimates between duel-energy X-ray absorptiometry and air displacement plethysmography

Assessment of body fat percentage is desirable to identify health risks associated with obesity. There are few studies that have compared the assessment of body fat between air displacement plethysmography and dual-energy x-ray absorptiometry, particularly related to age and gender differences. The purpose of this study was to determine if body fat percent estimates differ depending on age and/or gender between air displacement plethysmography (Bod Pod, Life Measurements Instrument, Concord, CA) and dual-energy x-ray absorptiometry (DEXA, General Electric Medical Systems, Lunar Prodigy, Madison, WI). Sixty subjects were studied: 15 men and 15 women, 22-35 years and 15 men and 15 women, 55-80 years. Subjects were excluded if they competed in athletics or high-level exercise training in the last year. Standard calibration and testing procedures were used for both methods. Both methods were administered at least twice to evaluate reliability and were repeated a third time if the first two measures differed by >2%. Differences between methods for age groups and gender were analyzed using ANOVA and reliability comparisons between the body composition methods were evaluated with correlation coefficients and Bland-Altman plots. Using data for all subjects, DEXA (r = .996) and Bod Pod (r = .985) both showed good reliability. However, in younger females the reliability of the Bod Pod (r = .911) was lower. Sixteen of the 60 subjects required a third trial for the Bod Pod, whereas all repeated DEXA measures were consistent. The deviation between trial 1 and 2 for the DEXA (.6%) was significantly less than that in the Bod Pod (1.5%). Significant interactions between the body composition method and age group were found. Mean body fat percentage in the younger group was higher in the DEXA (24.1 + 1.1%) than the Bod Pod (23.0 + 1.3%) however, in the older group it was found to be lower in the DEXA (33.9 ± 1.1%) than the Bod Pod (37.2 ± 1.3%). Both the DEXA and the Bod Pod were reliable but repeated DEXA measures were more consistent than the Bod Pod measures. Bod Pod estimates of body fat percentage were lower for younger subjects, yet higher for older subjects compared to DEXA measurements.School of Physical Education, Sport, and Exercise ScienceThesis (M.S.