Agreement of bioelectrical impedance with dual-energy X-ray absorptiometry and MRI to estimate changes in body fat, skeletal muscle and visceral fat during a 12-month weight loss intervention

The aim of the present study was to analyse the agreement of bioelectrical impedance analysis (BIA) compared with dual-energy X-ray absorptiometry (DXA) and MRI in estimating body fat, skeletal muscle and visceral fat during a 12-month weight loss intervention. A total of nineteen obese adults (twelve females, seven males) aged 20.2-48.6 years, mean BMI 34.6 (SE 0.6) kg/m(2), participated in the study. Body fat, skeletal muscle and visceral fat index were measured by BIA (Omron BF-500; Omron Medizintechnik) and compared with DXA (body fat and skeletal muscle) at baseline, 5 and 12 months, and with MRI (visceral fat) at baseline and 5 months. The subjects lost 8.9 (SE 1.8) kg (9.0 (SE 1.7)%) of body weight during the 12-month intervention. BIA, as compared to DXA, accurately assessed loss of fat (7.0 (SE 1.5) v. 7.0 (SE 1.4) kg, P=0.94) and muscle (1.0 (SE 0.2) v. 1.4 (SE 0.3) kg, P=0.18). While body fat was similar by the two methods, skeletal muscle was underestimated by 1-2 kg using BIA at each time point. Compared to MRI, BIA overestimated visceral fat, especially in males. BIA and DXA showed high correlations for kg fat, both cross-sectionally and longitudinally (r 0.91-0.99). BIA, compared with DXA and MRI, detected kg muscle and visceral fat more accurately cross-sectionally (r 0.77-0.87 and r 0.40-0.78, respectively) than their changes longitudinally (r 0.24-0.61 and r 0.46, respectively). BIA is at its best when assessing the amount or changes in fat mass. It is a useful method for measuring skeletal muscle, but limited in its ability to measure visceral fat.