Background: Body mass index is often used to assess adiposity but it does not differentiate between fat and non-fat components of body mass. However, body fat composition may be assessed using bioelectrical impedance analysis.
Objective: The study aimed to relate body mass index to fat in the assessment of overweight and obesity among adolescent Nigerians.
Methods: Adolescent pupils aged 10 years to 18 years from randomly selected secondary schools in Lagos, Nigeria were studied. Body mass index was calculated while percentage body fat was measured using Tanita body® fat scale model BF 681. Overweight and obesity were defined using age and sex specific criteria for body mass index and for body fat.
Results: There were 753 pupils {377(50.1%) males and 376(49.9%) females}. The overall mean values of body mass index for males and females were 18.1±2.72 and 18.9±3.41 (p < 0.05) respectively. The corresponding figures for body fat were 9.5±4.48 and 18.9±7.51 (p<0.05) respectively. About three quarters (76.2%) of the females who had body mass index in the overweight and obesity range had high body fat in comparison to 44.4% of males (p < 0.05).
Conclusion: Body mass index is more related to body fat in adolescent females than in their male counterparts.