A COMPARISON OF MEASUREMENTS OF LEAN BODY-MASS DERIVED BY BIOELECTRICAL IMPEDANCE, SKINFOLD THICKNESS AND TOTAL-BODY POTASSIUM - A STUDY IN OBESE AND NONOBESE NORMAL SUBJECTS

The measurement of body composition is an important part of metabolic and epidemiological research, but most currently available methods are complex and expensive. We have, therefore, compared measurements of fat mass (FM) and lean body mass (LBM), obtained using a commercially available bioelectrical impedance monitor (The Holtain Body Composition Monitor) (IMP), and by measuring skinfold thickness (SFT), with values obtained by measuring total body potassium (TBK). Twenty subjects, 10 with a body mass index (BMI) less than 30 (kg m-2), (non-obese) and 10 with BMI greater than or equal to 30 (obese) took part in the study. There was a strongly significant linear relationship between LBM calculated from TBK and that calculated from impedance (IMP), in both non-obese and obese groups analysed separately (non-obese: r = 0.92; p < 0.001 and obese: r = 0.92; p < 0.001) and together (all: r = 0.89; p < 0.001). LBM calculated from TBK was strongly linearly correlated with values derived from SFT for non-obese (r = 0.91; p < 0.001) but not for obese subjects. Mean values of LBM of non-obese subjects derived by each method were not significantly different (TBK: 51.3 +/- 10.40 kg; IMP: 53.18 +/- 10.37 kg; SFT: 48.87 +/- 9.48 kg), but significant differences existed when the subjects were obese (TBK: 51.86 +/- 9.65 kg; IMP: 58.69 +/- 8.55 kg; SFT: 67.61 +/- 8.14 kg: p < 0.01). The values of percentage body fat (%FM) calculated from TBK were strongly correlated with those derived by IMP (non-obese: r = 0.76; p = 0.001; obese: r = 0.97; p < 0.01; and all r = 0.96; p < 0.001) and SFT (non-obese: r = 0.78: p < 0.01; obese: r = 0.83: p < 0.01; all r = 0.94: p < 0.001). We conclude that the Holtain Body Impedance Monitor derives values of LBM and %FM that are strongly and significantly linearly correlated with values obtained using a standard method of calculating body composition (TBK). It is more accurate than SFT over a wider range of body weights when TBK is the reference.