Body Composition in Morbid Obesity: Correlation Between Body Adiposity Index and Bioelectric Impedance

Abstract

Introduction: Obesity has become an important public health problem. According, prevalence of morbid obesity is also growing. There is no consensus about the best method to measure body composition in morbid obesity individuals. A simple, easy, accurate, reproducible and inexpensive method is desirable. The aim of this study was to compare two methods that estimate body fat percentage (%BF), Body Adiposity Index (BAI) and Bioelectric Impedance (BI). Population and Methods: We prospectively evaluated 233 adults with indication for surgical treatment of morbid obesity at Bariatric and Metabolic Group at Hospital das Clinicas, University of Sao Paulo Medical School. All patients over eighteen years old were included after an Informed Consent and Agreement (Ethics Committee protocol number 8848). The data were collected before any intervention. Weight (Wgt) and height (Hgt) were measured in a Welmy scale. The circumferences were made with an inelastic tape-measure in a horizontal line. Waist circumference was the midpoint between the lower margin of the last palpable rib and the top of the iliac crest. Hip circumference (HC) was the maximum circumference of the buttocks. BI was made using Biodinamics equipment (model 310) with the person lies. Four electrodes were fixed in pairs in the right hand and bare feet. An electrical signal is introduced and an impedance value is obtained. This is then entered into an equation: BI= 23,25+(0,09xR)+ (1,00xWgt)-(0,08xHtg)+(0,13xYrs) (BI in kilograms of BF, R=resistance in owns, Wgt in kilograms, Htg in centimeters and age in years). BAI was determined according to the equation: BAI=(HC/Hgt x Hgt)-18 (BAI in %BF, HC in centimeters and Hgt in meters); Results: Mean age was 44±11.34 years and mean body mass index (BMI) was 49.13±7.65kg/m 2. The female prevalence was higher (78.5%) and 41.2% was super obese (BMI50kg/m 2). Mean BF was 52.15% (±6.04%) by BI and 51.49% (±8.22%) by BAI. The difference between than was 0.67% (±5.21%), interclass correlation of 0.74 (CI 95%:0.67-0.79). BAI had no significant error in women (p=0.611) and in super obese (p=0.368). A significant error was observed in men (p=0.06), in patients with BMI<50 kg/m 2 (p<0.001) and when the waist-hip ratio (WHR) was more than 1.06 (p=0,010). We observed that BAI underestimated %BF BI in men (2,44%), in patients with BMI<50 kg/m 2 (1,49%) and when the waist-hip ratio (WHR) was more than 1.06 (5,35%). Conclusion: BAI is an inexpensive and non-invasive method that was successfully used to determine BF in morbid obese adults, especially in women and super obese patients with a WHR less than 1.06.