What is Bioelectrical Impedance Analysis?
Bioelectrical impedance analysis (BIA) is a method for estimating body composition, particularly body fat and muscle mass.
It works by passing a weak electric current through the body and measuring the voltage to calculate the impedance (resistance and reactance) of the body. The method has become popular due to its ease of use and portability of the equipment.
The electrical impedance measured by BIA can be used to estimate total body water (TBW), which can then be used to estimate fat-free body mass and, by difference with body weight, body fat.
However, it is the 4-compartment model (4C) that is regarded as the reference method in body composition analysis, not BIA.
Do’s and don’ts while measuring BIA
Although BIA is straightforward to use, careful attention to the method of use should be given. Simple devices to estimate body fat, often using BIA, are available to consumers as body fat meters. These instruments are generally regarded as being less accurate than those used clinically or in nutritional and medical practice.
Disadvantages of using BIA instrument
Dehydration is a recognized factor affecting BIA measurements as it causes an increase in the body’s electrical resistance, so it has been measured to cause a 5 kg underestimation of fat-free mass, i.e., an overestimation of body fat.
Body fat measurements are lower when taken shortly after consumption of a meal, causing a variation between the highest and lowest readings of body fat percentage taken throughout the day of up to 4.2% of body fat.
Moderate exercise before BIA measurements leads to an overestimation of fat-free mass and an underestimation of body fat percentage due to reduced impedance. Therefore, it is recommended not to perform BIA for several hours after moderate or high-intensity exercise.