Bioimpedance, or bioelectrical impedance analysis (BIA), is a non-invasive method that estimates body composition and overall health. It measures the resistance electrical currents encounter as they travel through the body.
How Bioimpedance Works
Bioimpedance operates on the principle that different tissues within the human body conduct electricity uniquely. Lean body mass, which includes muscle, blood, and organs, contains a high percentage of water and electrolytes, making it a good conductor of electricity. In contrast, fat tissue has a lower water and electrolyte content, causing it to conduct electricity poorly. When a bioimpedance device is used, a small, harmless electrical current, typically around 70 microamperes (μA), is passed through the body.
As this current travels, the device measures the opposition it encounters, known as impedance. Impedance is composed of two main components: resistance and reactance. Resistance reflects the opposition to the current’s flow through the body’s water and electrolyte-rich tissues, primarily lean mass. Reactance, on the other hand, measures the resistance caused by cell membranes, which temporarily store electrical energy. By analyzing these resistance and reactance values, along with factors such as height, weight, age, and sex, the device can estimate various body composition parameters.
Measuring Body Composition and Hydration
Bioimpedance is commonly used to assess body composition, including body fat percentage and lean body mass. The device estimates the proportion of total body weight made up of fat, which helps track changes for fitness or health goals. It also provides an estimate of lean body mass, encompassing muscle, bone, blood, and organs, offering insights into overall muscle mass.
Beyond composition, bioimpedance also assesses the body’s total water content, including both intracellular and extracellular water. Monitoring total body water is important for understanding hydration status. Common devices that utilize bioimpedance include smart scales and handheld devices.
Factors Influencing Measurement Accuracy
The accuracy of bioimpedance measurements can be affected by several variables. Hydration status plays a significant role; dehydration can lead to an overestimation of body fat, while over-hydration can result in an underestimation.
Physical activity also influences measurements, as recent exercise can alter fluid distribution within the body. Food consumption before a measurement can affect results. Skin temperature and the placement of electrodes on the body are also factors that can introduce variability. The specific bioimpedance device and its underlying algorithm can also contribute to differences in readings. To track progress accurately, maintain consistent measurement conditions, such as taking readings at the same time of day and under similar hydration and activity levels.