Relationship between body mass index and body fat percentage, estimated by bioelectrical impedance analysis and skin fold thickness, in a group of sri lankan adolescents: A cross sectional study

Background: Body Mass Index, isoften used in clinical practice as well as in epidemiological studies.However, it is not clear how strong the relationship between BMI for age Z score (BMI – Z) and body fat percentage (BF %) among children.The study determined the (BMI – Z) and (BF %) relationship, in a group of South Asian adolescentsand to examined the influence of age, gender in this relationship andassessed its’ linearity or curvilinearity. Methodology: A cross-sectional study was conducted on 1374 adolescents. BF% was estimated by Bioelectrical Impedance analysis (BIA) and Skinfold thickness (SFT).Pearsons’ correlation coefficient(r) was calculated to see the relationship between (BMI – Z) score and (BF %). Multiple regression analysis was performed to determine the effect of age and gender in the relationship and polynomial regression was carried out to see its’ linearity. Results: Of the total sample 50.3 % (690) were girls. A significant positive correlation was observed between BMI – Z and BF% by SFT (Boys -r =0.87, p < 0.01; SEE = 4.42, Girls - r =0.78, p < 0.01; SEE = 4.17) and between BMI – Z and BF% by BIA (Boys -r =0.74, p < 0.01; SEE = 4.33, Girls - r =0.88, p < 0.01; SEE = 2.71). Effect of age and gender in the BMI – Z and BF%, relationship was significant (p < 0.001). Curvilinear relationship between BMI – Z and BF%, was found. Conclusion: BMI - Z is strongly correlates with BF % estimated by BIA and SFT in this study group. The both relationships studied were curvilinear in nature. The effect of the age and gender of an individual were significant.