Body fat estimation using bioelectrical impedance

I like excersice and I like fitness. Many times I have comments from friends about the body fat and I also found many people misusing the Bioelectrical Impedance Analysis (BIA). Actually some people don't even know what the BIA is and still use it.

Image 1. Person using a BIA

Image source: Excercisebiology

BIA and body fat estimation

The BIA is a widely used method for estimating body composition, especially the body fat. Despite the general idea that BIA gives you the body, it does not measure the body fat.

The BIA determines the electrical impedance of body tissues (opposition of a conductor to the flow of an alternating current), which provides an estimate of the total body water (TBW).

The impedance measured by BIA allows to estimate the body fat (BF), the fat free mass (FFM) and the body cell mass. Several studies analyzed suggested empirical equations developed by analyzing the physical characteristic of different populations; hence, they have different predictive accuracy.

Image 2. Comparison of predictive accuracy of different equations for estimating BF

Image source: Kao et al., 2010

Some suggestions before using BIA

Some suggestions about the use of BIA for estimating your body fat.

• Firm holding with of the BIA device. BIA will not provide the real body fat, but it does provide a reasonable guide. BIA does not provide the exact body fat, but it will indicate in you maintain a stable body fat, or if you tend to increase or reduce your body fat.
• Use the BIA at the same time. Our metabolism changes during the day. Impedance when we wake up is different than the impedance at noon of at night.
• Do not eat before BIA. Food intake, its absorption and the resulting increase in movement of fluid into the bloodstream from 2–4 hours before BIA measurement, decreases the impedance value and underestimates the body fat.
• Use BIA before exercising. Moderate exercise before using the BIA decrease the impedance and will underestimate the body fat. Underestimation due to exercise is twice the one due to eating.
• Use BIA under the same environmental conditions. Different environmental conditions may change the skin temperature and lead to different impedance.

Refernces & Further Reading
Bioelectrical impedance analysis in body composition measurement
Comparisson of different measurement equations for body composition estimation in male athletes