Is bioelectrical impedance used?

January 28, 2018

 

Our solution does not use bio-impedance. Research shows that bio-impedance is neither accurate or reliable. 

 

Bioelectrical impedance (BIA) use a weak electrical current to measure the amount of opposition, or impedance, the electrical current encounters when passing through the body. This, in theory, differentiates between fat mass and fat-free mass in the body.

 

Body fat scales which use BIA is a very popular way to measure body composition because of their simplicity.  Because of it's popularity, many believe it to be scientific, however, much of BIA information is inadequate.

 

"At least it is consistent, even if it isn’t accurate." Is the number one argument for using BIA.

However, that is not the case. Not only are BIA inaccurate, but they are inconsistently inaccurate. A change in bodyweight will cause a change in the bodies different tissues density.  Because of this, BIA inaccurately accepts two underlying issues: (1) the of estimates of the density of different body composition tissues (namely fat-mass, fat-free mass, muscle-mass, and skeletal mass) is the same from person to person, and (2) that the ratio of the density of these various tissues remains constant over time (even as you lose weight).  Also, BIA does not consider that different types of training (i.e. cardiovascular, strength training) elicit different effects on the density and composition of fat-free mass [1].

 

Even though a current runs through the body, many BIA devices do not measure the entire body. For example, a regular (foot-to-foot) body fat scales will only measure the fat-mass in the lower body.  The current only goes up one leg and down the other [2].

 

BIA results are also influenced by factors such as: the environment, your ethnicity, the phase of menstrual cycle a woman is in, underlying medical conditions of individuals, as well as hydration.  Changes in hydration also sway BIA results. BIA seems to interpret a change in body water as a change in fat mass [3]. If you are dehydrated, a BIA device will assume that you’ve lost fat. If you are well hydrated, the BIA device will assume you have gained fat.  Because of this, BIA has been deemed as invalid when measuring athletes body fat. Even the procedure for using BIA is often used incorrectly.  For most accurate results fasting is recommended, moderate to intense exercise 2-3 hours before measuring [4].  Even just twenty minutes after drinking 20-ounces of water, it has been shown that BIA body fat estimates increase [5].

 

BIA was the least accurate of all the methods (BMI, DEXA, Calipers), and has a margin of error as high as 8-9%.  An example of an error of 8% over time; an individual can lose 4% body fat, but the BIA device might display a 4% increase in body fat.  BIA is worse than BMI because BIA is so inconsistent [6].

 

BIA is used to track body fat percentage and help hit goals, to identify if your diet and exercise program is or is not working, and to give a formal body fat percentage reading for an individual. 

Because the margin of error is so large, BIA fails on all the above. 

 

1.Prior, Barry M., et al. "Muscularity and the density of the fat-free mass in athletes." Journal of Applied Physiology 90.4 (2001): 1523-1531.

 

2.Goldfield, G. S., et al. "Validity of foot-to-foot bioelectrical impedance analysis in overweight and obese children and parents." Journal of sports medicine and physical fitness 46.3 (2006): 447.

 

3.Saunders, Michael J., JENNIFER E. Blevins, and CRAIG E. Broeder. "Effects of hydration changes on bioelectrical impedance in endurance trained individuals." Medicine and science in sports and exercise 30.6 (1998): 885-892.

 

4. Dehghan, Mahshid, and Anwar T. Merchant. "Is bioelectrical impedance accurate for use in large epidemiological studies?." Nutrition journal 7.1 (2008): 26.

 

5. Dixon, C. B., et al. "The effect of acute fluid consumption on measures of impedance and percent body fat estimated using segmental bioelectrical impedance analysis." European journal of clinical nutrition 63.9 (2009): 1115.

 

6.Pateyjohns, Ian R., et al. "Comparison of three bioelectrical impedance methods with DXA in overweight and obese men." Obesity 14.11 (2006): 2064-2070.

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