Body composition method for assessing fat-free mass influences energy availability estimation in elite and pre-elite athletes

Energy availability (EA) is a critical factor in athletic performance and overall well-being, influencing athletes' physiological functions, training adaptations, and recovery. This study examined the impact of different body composition assessment methods [dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), and anthropometry] for assessing fat-free mass (FFM) on calculating and classifying EA in elite and pre-elite athletes. A total of 75 elite and pre-elite athletes (27 women; 24.9±5.9 years) were included in this study. EA was computed using each method's FFM estimate, and comparisons were conducted to evaluate differences in EA values, inter-method agreement, and shifts in EA categorization. The results revealed significant variations in EA depending on the FFM method employed (p < 0.001), with anthropometry yielding higher EA estimates than both BIA and DXA. Although strong correlations and high consistency were observed between methods (ICC = 0.982), discrepancies in classification were evident, particularly for individuals with EA values near clinical thresholds (i.e., 30 kcal/day/kg FFM or 45 kcal/day/kg FFM). BIA tended to overclassify low EA compared to DXA, while anthropometry more often identified individuals as having adequate EA. These findings highlight that choosing the FFM assessment method substantially influences EA estimation and its interpretation. Caution is advised when using BIA or anthropometry in applied settings, and the development of method-specific thresholds may enhance the accuracy and reliability of EA monitoring in athletic populations.