Changes of bioelectrical impedance after a body weight reduction program in highly obese subjects

We used bioelectrical impedance analysis (BIA) as an exploratory tool to mo nitor the changes in body composition induced by a short-term (3-wk) weight reduction (energy-restricted diet, moderate aerobic exercise conditioning and psychological counselling) in 175 highly obese subjects (body mass inde x, BMI=41.7+/-5.8 kg/m(2)). The decrease in weight and BMI after the weight reduction program was 3.4% (geometric mean, p<0.0001) and 3.7+/-1.3 kg/m(2 ) (mean+/-SD,p<0.0001), respectively, Bioelectrical impedance (Z) increased of about the same value at each of the measured frequencies (from 6+/-10% at 5 kHz to 5+/-9% at 100 kHz, mean+/-SD, p<0.0001), A statistically signif icant increase in Z(5):Z(100) was also seen (p<0.0001), but its clinical si gnificance is questionable owing to its low absolute value (<1%). Taken tog ether, these data suggest that no clinically relevant change in body water distribution occurred in our subjects as a result of the weight reduction p rogram. However, the changes in Z did not satisfactorily predict the change s in anthropometric dimensions despite the evidence of a substantial associ ation between Z and anthropometry both before and after the weight reductio n program, Thus, accurate predictions of body composition changes in obese subjects may require more than two BIA measurements so as to have a better description of the weight-losing process. (C) 2000, Editrice Kurtis.