Effect Of Acute Feeding On Bioelectrical Impedance Vector Analysis Calculated Phase Angle In Healthy Subjects

Phase angle (PhA) calculated via bioelectrical impedance vector analysis (BIVA) is a measure of body cell mass and hydration that is commonly used to detect fluid imbalance and nutritional status. Phase angle is derived from the raw impedance values resistance (R) and reactance (Xc), obtained from multi-frequency bioelectrical analysis (MF-BIA). Currently there are no studies investigating the effect of acute feeding on measures of PhA obtained by MF-BIA. PURPOSE: To determine the effect of acute feeding on PhA. METHODS: Thirty-eight young adults (Age: 21.9 ± 3.1 yrs; Height: 174.1 ± 8.7 cm; Weight: 72.1 ± 9.9 kg; BMI: 23.5 ± 1.9 kg/m2) were randomized to four conditions; high carbohydrate (CHO: 116.5 g CHO; 86% of meal), high protein (PRO: 63.5 g PRO; 58% of meal), ad libitum mixed (MX: 67 g CHO, 21 g PRO; 25 g FAT) and fasted (FAST: 8 hr fast). Meals were consumed one hour prior to MF-BIA measurement. Bioelectrical impedance was measured using a tetrapolar stand-up MF-BIA device. Subjects stood for five minutes prior to measurement on the device’s scale with the soles of their feet positioned on four corresponding electrodes; subjects held the handles in both hands making contact with corresponding electrodes on the thumbs and palm of each hand as impedance was measured. Separate one-way ANOVAs were used to compare PhA of the whole body (WB), trunk (TR), right arm (RA), and right leg (RL) between feeding groups. RESULTS: There was no significant difference in PhA between feeding groups for WB (p = 0.985, mean ± SD = 6.46 ± 0.71°), TR (p = 0.918, mean ± SD = 8.95 ± 1.64°), RA (p = 0.903, mean ± SD = 5.82 ± 0.79°), or RL (p = 0.988, mean ± SD = 7.03 ± 0.57°). CONCLUSION: The lack of difference between PhA values across feeding groups suggests that acute feeding does not alter hydration-sensitive MF-BIA measures of impedance values. This could indicate that current measuring practices, which typically require participants to be fasted, may not be necessary to obtain reliable body composition values.