COMPARISON OF NEAR-INFRARED LIGHT SPECTROSCOPY, BIOELECTRICAL IMPEDANCE AND TRITIATED-WATER TECHNIQUES FOR THE MEASUREMENT OF FAT-FREE MASS IN HUMANS

Fat-free mass (FFM) was measured with three different methods: near-infrared spectroscopy, bioelectrical impedance and tritiated water technique, in 76 (39 females/37 males) subjects (age 47+/-2 [SEM] years, BMI 26.8+/-0.6 kg m-2). From bioelectrical impedance measurements FFM was calculated with manufacturers formula and a formula developed by Deurenberg et al [1]. FFM estimated from tritiated water technique (51.9+/-1.1 kg) was significantly lower than measured with near-infrared spectroscopy (57.4+/-1.4 kg; p<0.001) and bioelectrical impedance calculated with manufacturers formula (59.6+/-1.5 kg; p<0.001), but did not differ from the estimation made according to Deurenberg (52.1+/-1.2 kg). All the methods were highly intercorrelated, although the correlation coefficients were lower in the obese than lean subjects. Obesity seems to influence the bioimpedance method more than the near-infrared spectroscopy method. The results demonstrate that the near-infrared spectroscopy and the bioelectrical impedance method are simple and reproducible techniques to estimate fat-free mass in normal weight man. Both measurements are based partly on the anthropometric measurements. However, it is necessary to use an adjusted formula to obtain reliable measures of fat-free mass with the bioimpedance method in obese subjects.