Assessment of body fat content using bioelectrical impedance analysis in relation to body mass index among adults aged 18-55 years in tertiary institutions in Lusaka

Abstract

Accurate measurement of body fat mass (BFM) is critical in assessing overweight and obesity that pause health implications of other non-communicable diseases (NCDs). The traditional commonly used method, body mass index (BMI) is not adequate to measure BFM because it does not account for body composition. Hence the study measured BFM and free fat mass (FFM) using bioelectrical impedance analysis (BIA) in relation to BMI. This allowed for better estimation of human nutritional status and determination of misclassification when BMI method is used alone. A total of 247 participants, comprising 54% females and 46%males aged 18-55 years were selected from University of Zambia (UNZA), Chalimbana University (CHAU), Natural Resources Development College (NRDC) and Chongwe College of Education (CCE). Participants were further categorized into young adults aged 18-39 years (77%) and old adults aged 40-55 years (23%). Both measurements of BMI and BIA were taken in the morning following overnight fasting Statistical package for social sciences (SPSS) was used to analyze data. Descriptive statistics were used to characterize participants while inferential statistics applied a 95% confidence interval (CI). Results showed Pearson correlation BMI and BFM (r=0.660), age BMI (r=0.372) and BFM (r=0.273), sex BMI (r= -0.273), and BFM (r=-676). The ANOVA and t-test associations for all parameters gave p<0.001. Age regression (coefficient =0.372 BMI; 0.273 BFM, p< 0.001) and sex effect (coefficient= -0.273 BMI; -0.676 BFM, p< 0.001) .Cross tabulation of World Health Organization (WHO) cut offs for BMI against BFM reviewed a difference of 82.2%. In all categories BFM values were higher than BMI and differences were significant (p<0.001), though correlated positively (r=0.660). As BMI increased BFM also increased. Both age and sex indicated significant influence on BMI and BFM whilst the correlation reflected positive for age and negative for sex. This study showed that BMI in relation to BIA underestimates BFM if used as a proxy which leads to misclassification of nutritional status. Increase in age translated into increased BMI and BFM. Lower BMI and BFM values were observed in men in relation to females and increased BMI and BFM in old adults in comparison with young adults. Thus BIA can be used to supplement BMI in diagnosis and management of problems associated with overweight and obesity. Key words: Body Fat Mass (BFM), Free Fat Mass (FFM), Body Mass Index (BMI), Bioelectrical Impedance Analysis (BIA) and Non Communicable Diseases (NCDs).