No differences in the body fat after violating core bioelectrical impedance measurement assumptions

Objective: It is unclear to what degree acutely violating bioelectrical impedance analysis (BIA) measurement assumptions will alter the predicted percent fat mass (%FM) and whether this differs by sex or body mass index (BMI). Methods: %FM was assessed under control, dehydration, exercise, water, meal intake and non-voided bladder conditions with three BIA devices (Tanita: BC-418, TBF-314, & Omron HBF-306CN) (n=40). Results: For all BIA devices, there were no differences in the %FM values between the control and the other conditions in men or women (-1.9 to 0.4%, p >0.05). Across the three devices and five conditions, 97% of %FM tests returned values within 5% of control (2 tests), and 86% of tests were within 2% of control despite violating an assumption. The errors were greatest with dehydration and females were more likely to have a %FM difference greater than 2% than males with dehydration using the hand-to-foot device (Tanita TBF-314: 59% versus 9%). There were no differences in %FM between control and the conditions when examined by BMI category (overweight: -2.8 to 0.1% and normal weight: -1.7 to 0.5%; BMI*trial, p=0.99). Conclusion: %FM estimates were similar despite acutely violating the preliminary measurement BIA assumptions across a range of different BMIs. The minor variations in %FM are smaller than what would be expected with day-to-day variability or weight loss intervention, but may be larger in women than men.