Dual-Energy X-Ray Absorptiometry Accurately Tracks Fat-Free Mass Changes in Older Men and Women: A Four-Compartment Molecular Model Validation

Accurately tracking changes in fat-free mass (FFM) in older adults is of importance due to the reduction of muscle mass with age and the subsequent onset of sarcopenia. PURPOSE: The purpose of the current investigation was to determine if dual-energy X-ray absorptiometry (DXA) could accurately track FFM changes in older adults compared to a criterion four-compartment (4C) model. METHODS: Forty men (n = 20) and women (n = 20) participated in a six-month progressive strength training program while the remaining men (n = 22) and women (n = 24) acted as controls. Participants consisted of healthy older adults ages 65 to 88. Body composition was assessed using DXA and a 4C model that included bone mineral content from DXA, body volume from air-displacement plethysmography, and total body water using deuterium oxide. RESULTS: Mean delta differences in both the exercise (0.211 kg) and control (−0.007 kg) groups were not significant (p > 0.26) for either men or women comparing DXA to the 4C model. Individual differences were less than +/− 2.97 kg. DXA accurately tracked all but one subject in the exercise group (5%) and one subject in the control group (3%) when the minimal difference needed to be considered real (MD) for DXA (1.44kg) was exceeded or not met, respectively. CONCLUSION: With an overall individual accuracy of 96%, DXA can be considered a valid tool for tracking FFM changes in aging adults. DXA produced valid delta values compared to the 4C model in both men and women in the control and exercise groups. Due to the non-significant CE values, low TE values, and high individual accuracy, DXA appears to be valid for tracking changes in older adults. However, caution should be used when interpreting values that have not met the MD. PRACTICAL APPLICATION: When the MD for DXA FFM is exceeded, DXA can be used for individually assessing FFM changes in aging adults with an accuracy of 96%. However, this accuracy only represents individual directional changes and not the magnitude of the FFM changes. Therefore, individual errors may be as large as +/− 2.96 kg when quantifying changes in FFM using DXA compared to a 4C model. Nonetheless, DXA can be considered an accurate tool for tracking FFM in older men and women when changes reported by DXA exceed 1.44 kg. ACKNOWLEDGEMENTS: We would like to thank Abbott Nutrition for funding this study.