The effect of a meal on measures of impedance and percent body fat estimated using contact-electrode bioelectrical impedance technology

BACKGROUND/OBJECTIVES: To determine the effect of a meal on impedance and percent body fat (%BF) determined using contact-electrode bioelectrical impedance analysis (BIA) technology. SUBJECTS/METHODS: Forty-three adults (23 women and 20 men) volunteered to participate in this study (age = 20.5 +/- 1.1 years; body mass index = 24.1 +/- 3.8 kg/m(2)). Body composition was assessed using three BIA analyzers: leg-to-leg (LBIA), segmental (SBIA) and multi-frequency (MFBIA), on two separate occasions. After a baseline measurement, subjects consumed a meal or received nothing, which served as the control (CON). Subjects were reassessed 20, 40 and 60 min following (POST) the baseline measure in each condition. RESULTS: Twenty minutes after eating (3847 +/- 900 kJ), body mass (LBIA = 0.8 kg, SBIA = 0.8 kg, MFBIA = 0.7 kg, P<0.05), impedance (LBIA = 6.0 Omega, SBIA = 17.9 Omega, MFBIA = 27.1 Omega, P<0.05) and %BF (LBIA = 0.9%, SBIA = 1.7%, MFBIA = 0.8%, P<0.05) increased significantly and remained elevated at 60 min POST. During the CON trial, a consistent body mass reduction (60-80 g) and impedance increase (4-9 Omega) was observed over time resulting in a small increase in %BF (0.3-0.7%) 60 min POST (P<0.05). CONCLUSIONS: Twenty minutes after eating, %BF increased due to elevations in impedance and body mass. As such, when precision is critical, we recommend adhering to the pretest fasting guidelines to avoid meal-induced alterations in %BF estimates. In addition, use of a consistent testing schedule may minimize normal %BF variation over time.