What Is Bioelectrical Impedance Analysis and How Accurate Is It?
When you sign up for a new gym, you might be introduced to a piece of equipment known as a 'bioelectrical impedance analysis' machine, often touted as a reliable tool for measuring body fat. While these body scanners offer quick and accessible results, it's crucial to recognise that they fall short of being the 'gold standard' in body composition measurement. Understanding the limitations of bioelectrical impedance analysis can help you better interpret your results and avoid potential inaccuracies
We explain what bioelectrical impedance analysis is, list the pros and cons and give our verdict so that you can decide if it's right for you.
What Is Bioelectrical Impedance Analysis?
Bioelectrical impedance analysis (BIA) is a method used to estimate body composition — mainly body fat and muscle mass. It works by measuring the resistance (or impedance) of body tissues to a small electrical current that is passed through the body.
While not 100% accurate, bioelectrical impedance analysis is widely used in gyms, clinical settings and even inbuilt into bathroom scales, as it's a quick and relatively easy method to assess body composition.
A review published in the International Journal of Clinical Nutrition stated that bioelectrical impedance analysis can measure:
Fat mass
Fat-free mass
Total body water
How Does Bioelectrical Impedance Analysis Work?
Different tissues in the body conduct electricity in different ways. For example, muscle and water are good conductors and will have lower impedance (resistance), whereas fat, which is a poor conductor, will have higher impedance.
During a bioelectrical impedance analysis test, electrodes are usually placed on the hands, feet, or both. Sometimes you will hold onto handles of a piece of equipment, or stand barefoot on scales. A small electrical current is sent through the body and the device measures the resistance to the current as it passes through different tissues.
The bioelectrical impedance analysis device uses impedance measurements along with factors like height, weight, age, and sex to estimate your body fat percentage, muscle mass, water content, and sometimes other variables such as the bone-to-muscle ratio.
Is Bioelectrical Impedance Analysis Accurate?
The accuracy of bioelectrical impedance analysis can vary depending on several factors, and while it provides useful estimates, it is not the most precise method for measuring body composition and has some limitations. It's important to be aware of:
Bioelectrical impedance analysis relies on your body's water content to estimate body composition. Since water is a good conductor of electricity, dehydration or over-hydration can significantly affect the results. Dehydration may lead to overestimating body fat, while being over-hydrated can underestimate it.
The accuracy of different bioelectrical impedance analysis devices can vary widely. Professional grade devices found in clinical settings tend to be more accurate than other devices found in home scales.
Factors like our age, gender and ethnicity can influence the accuracy. Bioelectrical impedance analysis devices use algorithms to estimate body composition based on these factors, and the accuracy of these algorithms can vary.
To get consistent and more accurate results, it's important to standardise the conditions under which bioelectrical impedance analysis measurements are taken. Measurements should be taken at the same time of day, in a fasted state, after going to the toilet, and without recent exercise, as these factors can affect total body water and distribution.
Bioelectrical impedance analysis is less accurate compared to more advanced and direct methods of measuring body composition, such as dual energy X-ray absorptiometry (DEXA), hydrostatic weighing, or air displacement plethysmography (Bod Pod) or body fat calipers. These methods are considered more reliable but are also more expensive, require experience of use and are less accessible.
What Are the Risks of Bioelectrical Impedance Analysis?
Bioelectrical impedance analysis is generally safe but certain risks exist particularly for anyone with implanted medical devices like pacemakers, as the small electrical current used could interfere with these devices. Some may experience skin irritation from the electrodes, however the main concern lies in the potential for inaccurate results due to factors like hydration levels, which can lead to misinterpretation and then misguided health decisions.
The Verdict: Bioelectrical Impedance Analysis
Bioelectrical impedance analysis provides an estimate of body composition and is fairly helpful for tracking rough changes over time rather than obtaining a precise measurement at a single point. It is probably more useful in clinical and large research settings, where variables which effect results can be controlled precisely. This is supported by evidence published in the European Journal of Clinical Nutrition.
If used consistently under controlled conditions, bioelectrical impedance analysis can be a somewhat useful tool, but it's important to be aware of its disadvantages and potential room for error. It should be used with an understanding of its limitations and under professional guidance. While more expensive and invasive, other methods such as DEXA scans are superior for more accurate measurements and considered the 'gold standard'.
Bioelectrical impedance analysis can be used as a rough ball park to measure body fat percentage, so if it's all you have access to, it's not going to hurt necessarily. Just don't place too much weight on the results and make sure you standardise the conditions when using it such as measuring:
At the same time of day
After going to the toilet
Before eating in fasted state
Not after exercise
When adequately hydrated
You can find out how to measure you body fat percentage accurately, here.
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