Bio-electrical impedance (BIA)

Bio-electrical impedance (BIA)

LASA filenames:

Contact: Marjolein Visser

Bioelectrical impedance is a method to estimate body composition using a prediction equation and measurements of reactance and resistance of the body. The measurements are generally obtained by placing four surface electrodes on the hand and foot, through which a low electrical current at a single or at multiple frequencies is applied. As body water and lean tissue conduct an electrical current rapidly, and body fat acts as an insulator, the electrical properties of the body are highly correlated with the composition of the body.

BIA is portable and safe, the procedure is simple and non-invasive, and the results are reproducible and rapidly obtained. More information on the principles of bioelectrical impedance can be found in reference 1.

Measurement instruments in LASA
The measurement has been conducted in a small subset (N=247) of the baseline examination in 1993 in collaboration with Wageningen University.  Unfortunately, no detailed information about these measurements has been kept.  What we do know is that a single-frequency (50 kHz) apparatus was used with four electrodes (two on hand and wrist and two on ankle and foot). The participant was lying down with the arms not touching the trunk and the legs separated. Very likely the measurement was conducted on the right side of the body.

The measured resistance (bmresist) and reactance (bmreacta) by BIA can be used to predict body composition using published prediction equations. Equations for the prediction of fat mass, body fat percentage, total body water, fat-free mass and skeletal muscle mass are available in the literature. These equations very often require information on body height, body weight, age and sex. Please note that the predicted values can be used on a group level, but due to individual prediction errors any individual value should be interpreted with care.

 All bioelectrical impedance measurements should be carefully interpreted for respondents for which edema of the legs was indicated (variable=bmedema), as edema reduces the resistance of the body and can lead to an overestimation of lean body mass and muscle mass.

Frequently used and validated equations for older adults
Sergi (2) equation for appendicular skeletal muscle mass (ASMM):

This equation is based on measurements in 296 free-living, healthy Caucasian subjects (117 men, 179 women) over 60 years of age (range 60-85 y) and a mean BMI of 27.0 kg/m2 (range 19.3–38.0). Dual-energy x-ray absorptiometry (DXA) was used as the reference method (fan-beam densitometer, Hologic QDR Discovery A, Hologic Italy). The BIA device used was the whole-body tetrapolar BIA (BIA 101 Anniversary AKERN/RJL Systems; Florence, Italy) with an alternating sinusoidal electric current of 400 μA at a single operating frequency of 50 kHz. The equation was developed by means of a double cross-validation technique.

Parameters needed for the equation:

Height = total body height (cm)
Resistance at 50 kHz (Ohm)
Weight = total body weight (kg)
Sex = men=1, women=0
Reactance at 50 kHz (Ohm)


ASMM(kg) = −3.964 + (0.227*height2/resistance) + (0.095*weight) + (1.384*sex) + (0.064*reactance)
[R2 = 0.92 and SEE = 1.14 kg].

Kyle (3) equation for fat-free mass (FFM): This equation is based on healthy subjects (202 men and 141 women) aged 20-94 y (n=119 (49%) were aged 60 and older). FFM was measured by dual-energy x-ray absorptiometry (Hologic QDR-4500 instrument, Waltham, MA, USA) and enhanced whole body 8.26a software. The used bioelectrical impedance analyzer was a Xitron 4000B, 5-kHz, with 0.8-mA electric current (Xitron Technologies, San Diego, CA, USA). The prediction equation for BIA was developed by using a double cross-validation technique.

Parameters needed for the equation:

Height = total body height (cm)
Resistance at 50 kHz (Ohm)
Weight = total body weight (kg)
Reactance at 50 kHz (Ohm)
Sex = men=1, women=0


FFM (kg) = -4.104 + (0.518*height2/resistance) + (0.231*weight) + (0.130*reactance) + (4.229*sex)
[R2= 0.972 and SEE = 1.72 kg]

Variable information


Availability of information per wave




¹ More information about the LASA data collection waves is available here.

* 2B=baseline second cohort;
3B=baseline third cohort;
MB=migrants: baseline first cohort

Me=data collected in medical interview


Previous use in LASA
These data have not been used in LASA yet.


  1. Kyle UG, Bosaeus I, De Lorenzo AD, Deurenberg P, Elia M, Gómez JM, Heitmann BL, Kent-Smith L, Melchior JC, Pirlich M, Scharfetter H, Schols AM, Pichard C; Composition of the ESPEN Working Group. Bioelectrical impedance analysis–part I: review of principles and methods. Clin Nutr. 2004 Oct;23(5):1226-43.
  2. Sergi G, De Rui M, Veronese N, Bolzetta F, Berton L, Carraro S, Bano G, Coin A, Manzato E, Perissinotto E. Assessing appendicular skeletal muscle mass with bioelectrical impedance analysis in free-living Caucasian older adults. Clin Nutr 2015; 34: 667–73.
  3. Kyle UG , Genton L, Karsegard L,  Slosman DO, Pichard C. Single prediction equation for bioelectrical impedance analysis in adults aged 20–94 years. Nutrition. 2001 Mar;17(3):248-53.

Date of last update: October, 2023 (first version)