Are under- and overweight female elite athletes thin and fat? A controlled study

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.

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.

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.

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.