Bioelectrical Impedance Analysis (BIA)

Bioelectrical impedance analysis (BIA) is a method for measuring body composition based on the rate at which an electrical current travels through the body. Body fat (adipose tissue) causes greater resistance (impedance) than fat-free mass and slows the rate at which the current travels. BIA scales estimate body fat percent using bioelectrical impedance analysis.

What Is Bioelectrical Impedance Analysis?

You've probably seen body fat scales on store shelves or online that use bioelectrical impedance analysis. Since the scales can be expensive, you've probably wondered what is bioelectrical impedance analysis and is it worth paying for?

The definition of bioelectrical impedance analysis sounds fairly complicated. But BIA scales use straightforward technology. The scales measure the rate at which a painless electrical current travels through your body. Based on that rate, a calculation is used to estimate fat-free mass and body fat percent.

There are different types of BIA devices. Most body fat scales use foot-foot bioelectrical impedance analysis. This means that when you use the device, you place each foot on a pad and the current travels through your body between your feet. But there are also hand-to-foot BIA devices, hand-to-hand and foot-to-hand devices, as well.

Are Bioelectrical Impedance Analysis (BIA) Scales Accurate?

Some studies have shown that bioelectrical impedance analysis is a fairly accurate method for estimating body fat. But these research studies generally don't not test the scales you find in the store. And experts generally agree that the accuracy of the measurement depends, in part, on the quality of the device.

In addition, there are other factors that may affect a reading when you use a BIA scale. 

• Body weight.  Studies have shown that bioelectrical impedance analysis may be less accurate in obese people.
• Hydration level. Some studies have found that dehydration may cause fat-free mass (muscle and bone) to be underestimated.
• Recent exercise activity. High-intensity exercise may affect the accuracy of BIA readings
• Training load. Some scales have a special setting for athletes who train more often. The settings are intended to increase accuracy.
• Recent food or drink intake.  The results of some studies suggest that BIA is more accurate after overnight fasting.

Some researchers also say that ethnicity and environmental factors (like skin temperature) can affect the accuracy of BIA measurements.

Should You Buy a BIA Body Fat Scale?

Even if you get an accurate reading on a BIA scale, the number represents an estimate of your total body fat percent. Bioelectrical impedance analysis does not provide an exact measurement of your total body fat. The scales also cannot tell you where fat is located on your body.

So is it worth it to buy a scale that uses bioelectrical impedance? For many people, it might be.

Even though there are many factors that can affect the accuracy of your reading, a BIA scale used regularly can show you changes in your body fat over time. So even though the actual number may not be perfect, you may be able to track changes to your body composition with diet or exercise.

Additionally, if you use a fitness tracker by brands like Fitbit, you can get a scale to pair with the device and track all of your body metrics in one place. The Fitbit Aria 2 wi-fi smart scale that measures weight, body fat, and body mass index. The numbers seamlessly sync with the Fitbit dashboard so you can see how the numbers develop over time along with daily activity and diet changes.

Since many BIA scales offer several features for a reasonable cost and because it is a quick and easy way to estimate body fat percent, body fat scales that use bioelectrical impedance analysis are a worthwhile investment for many consumers.