Reference values of fat mass index and fat-free mass index in healthy Spanish adolescents

Introduction: body mass index (BMI) does not allow to discriminate the composition of the different body compartments. The aim of this study was to develop reference values for the fat mass index (FMI) and fat-free mass index (FFMI) in healthy adolescents using anthropometric techniques in order to provide reference standards for daily clinical practice. Methods: a cross-sectional study in 1,040 healthy Caucasian adolescents (470 boys and 570 girls) aged 10.1 to 14.9 years. Weight, height, and skinfold thickness were recorded, and BMI, percentage of total body fat, FMI and FFMI, and FMI and FFMI percentiles were calculated. Results: FFMI and FMI percentiles for healthy adolescents (both sexes) categorized by age are displayed. In boys a significant increase in FFMI is observed, and both the percentage of total body fat and FMI significantly decreased. In contrast, in girls the percentage of body fat mass, FMI, and FFMI significantly increased. Except at 10 years of age, FMI was higher (p < 0.05) in girls at all ages. FFMI was higher (p < 0.05) in boys at all ages. Conclusions: reference values of FMI and FFMI would be a very useful instrument in clinical practice for the diagnosis and. especially, the analysis of body composition changes during the treatment of childhood obesity.