Purpose: The study's purpose was to relate body mass index (BMI) to body fat percentage as measured by dual-energy x-ray absorptiometry in female elite athletes from different sports and nonathletic controls and to investigate what characterizes the athletes with unhealthy low and high body fat values.
Methods: This study was conducted in three phases: 1) screening with a detailed questionnaire, 2) body composition measurement (dual-energy x-ray absorptiometry), and 3) clinical interview. All female elite athletes representing national teams at the junior or senior level age 13-39 yr (n = 938) and an age group-matched randomly selected population-based control group (n = 900) were invited to participate. A stratified random sample was invited to participate in parts 2 and 3. A total of 186 athletes (62%) and 145 controls (48%) participated in all three phases.
Results: Of those athletes with normal BMI values (18.5-24.9 kg·m⁻²) (n = 150), 2.0% were classified with low body fat levels (<12%), and 6.7% were classified with obese body fat levels (≥ 33%). The median value for the entire group was 24.3% body fat. For the controls with normal BMI values (n = 96), none was classified with low body fat levels, and 50% were classified with obese body fat levels (median = 33.1%). The correlation between BMI and body fat percentage was 0.671 (P < 0.01) (SEE = 5.3%) for the athletes and 0.813 (P < 0.01) (SEE = 4.1%) for the controls. Both under- and overfat athletes self-reported menstrual dysfunction, stress fractures, history of weight fluctuation, and use of pathogenic weight control methods and were diagnosed with clinical eating disorders and/or low bone density.
Conclusions: Our data show that BMI is not a valid measure for assessing or monitoring body composition in female elite athletes, and it should be used carefully in female nonathletes.