Comparison of near-infrared light spectroscopy, bioelectrical impedance and tritiated water techniques for the measurement of fat-free mass in humans

Abstract

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.

Key Words:

• bioelectrical impedance
• fat-free mass
• near-infrared spectroscopy
• tritiated water