Bioelectrical Impedance Analysis (BIA) Body Fat Testing

man pinching stomach fat
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Bioelectrical Impedance Analysis (BIA) is a method of measuring body fat percent by sending a low-level, safe, electrical current through the body.  It is one simple method of determining a person's body composition and body fat percentage.

How Bioelectrical Impedance Analysis Works

The current travels at a different rate through the various body tissues, which then allows a calculation of fat mass and fat-free mass.

This feature is common in many of today's at-home digital scales.

The current passes easily through muscle tissue (which contains a large amount of fluid), but it travels slowly as it passes through fat tissue. The resistance encountered as the current hits the fat tissue is called bioelectrical impedance. The rate at which the electrical current travels through your body estimates the amount of fat-free mass you have. It does this by also taking in consideration how tall you are, your gender, and weight measurements, these calculations determine your body fat percentage.

Types of BIA Devices

There are a variety of BIA devices available, and all use the same basic principles to determine body fat. Some of the more popular brands include Omron, Tanita, and HealthTools EatSmart.

The most common devices use foot-to-foot BIA, such as a scale, but some are handheld, which use hand-to-hand BIA, as well as some hand-to-foot and foot-to-hand BIA devices.

For illustration let’s use the scale as an example as to how they work. When you step on the pads of a BIA scale, the current travels through your body between your feet.

Are Measurements Accurate?

For the most part, bioelectrical impedance analysis has proven to be a fairly accurate method for estimating body fat in a laboratory setting.

However, the scales that are in your bathroom are usually not what’s being used in research studies. Accuracy of the measurement has a lot to do with the quality of the product as well as other factors.

While the readings can be affected by hydration levels, food intake, skin temperature, and other factors, like weight. Ironically, there is some proof that BIA isn't accurate in obese people as well as very athletic ones. Apparently, when your body composition leans one way or another, it may throw off BIA results.

What you have to remember is that these are estimates, not absolutes; especially if you are using a BIA scale. Even though the actual number may not be perfect, it can still enable you to track changes to your body composition with diet or exercise.

The key to getting a BIA scale to work for you is to follow the directions and take the reading under similar conditions each time. If you track your readings, then you can see if what you are doing is making a difference toward achieving your body composition goals.

For reasons what body composition really means, you can read about how body composition is different from body fat percentage, or you can read about the gold standard of measuring body composition.



ACSM's Guidelines for Exercise Testing and Prescription, Seventh Edition

Alvarez VP, et al. Single frequency bioelectrical impedance is a poor method for determining fat mass in moderately obese women. Obesity Surgery. 2007 Feb.

International Standards for Anthropometric Assessment (2001), The International Society for the Advancement of Kinanthropometry (ISAK)