Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population

Clinical Nutrition ESPEN xxx (xxxx) xxx

Contents lists available at ScienceDirect

Clinical Nutrition ESPEN journal homepage: http://www.clinicalnutritionespen.com

Short Communication

Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population Spyridon Kanellakis*, Efstathios Skoufas, Eva Karaglani, Georgia Ziogos, Aimilia Koutroulaki, Flora Loukianou, Maria Michalopoulou, Amalia Gkeka, Foteini Marikou, Yannis Manios Department of Nutrition & Dietetics, Harokopio University of Athens, El. Venizelou 70 Str, P.C.176 76, Athens, Greece

a r t i c l e i n f o

s u m m a r y

Article history: Received 5 June 2019 Accepted 8 January 2020

Background and aims: Excessive body fat accumulation is associated with adverse health effects; therefore its accurate and reliable assessment is of great significance. The aim of the study was to develop and validate an easy and applicable equation, based on bioelectrical impedance analysis, estimating fat free mass in Greek general population and compare it with those of the literature. Methods: Anthropometric and bioelectrical impedance parameters were obtained from 694 Greek adults (429 women and 265 men) so as to develop and validate the equation, using DXA as reference method. The validation and the reliability of the equation were examined with Bland-Altman analysis and Intraclass Correlation Coefficient (ICC). Results: The developed prediction equation was FFM (kg) ¼ 12.299 þ (0.164 * Weight (kg)) þ (7.287 * Gender (0:female, 1:male)) e (0.116 * Resistance (ohm)/Height (m)2) þ (0.365 * Reactance (ohm)/Height (m)2) þ (21.570 * Height (m)) (R2 ¼ 0.944, p < 0.0001). Regarding the current population, the current equation presented the lowest bias (0.069 kg, p ¼ 0.707) and the highest ICC (0.985) compared to those of the literature. Conclusion: The current prediction equation was found to be valid and reliable in a representative sample of the Caucasian Greek general population and its utilization for body composition assessment could be an alternative of using labor-intensive, expensive and time-consuming reference methods. © 2020 European Society for Clinical Nutrition and Metabolism. Published by Elsevier Ltd. All rights reserved.

Keywords: BIA Body composition Bioelectrical impedance analysis Caucasian

1. Introduction Elevated body fat accumulation is associated with increased mortality, therefore the assessment of human body composition has a key role in the risk detection [1]. The assessment of body composition with reference methods includes underwater weighing, deuterium oxide dilution, dual energy X-ray absorptiometry (DXA) and Bod Pod. Still, they are very difficult to be applied, sometimes even in research, due to the fact that they are labor intensive, time consuming and expensive. In addition,

* Corresponding author. Harokopio University, 17671, Kallithea, El Venizelou 70, Athens, Greece. E-mail address: [email protected] (S. Kanellakis).

anthropometry models require well trained and standardized personnel so as to provide accurate results [2]. Alternatively, Bioelectrical Impedance Analysis (BIA) has been used in large scale studies of body composition and assessment of fat free mass and is characterized as a safe method with high sensitivity and convenience for the patient [3]. In the literature, a large number of equations estimating fat mass (FM) and fat free mass (FFM) is available. Although the use of specific population equations is necessary for the accurate estimation of body composition, there are few anthropometric equations estimating body composition in Greek population incorporating BIA variables [4e6]. Therefore, the primary aim of the current study was to develop and validate an equation derived from BIA and anthropometric

https://doi.org/10.1016/j.clnesp.2020.01.003 2405-4577/© 2020 European Society for Clinical Nutrition and Metabolism. Published by Elsevier Ltd. All rights reserved.

Please cite this article as: Kanellakis S et al., Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population, Clinical Nutrition ESPEN, https://doi.org/10.1016/j.clnesp.2020.01.003

2

S. Kanellakis et al. / Clinical Nutrition ESPEN xxx (xxxx) xxx

data, respectively, which best predicts body FFM in Caucasian adult and specifically Greek population. The secondary objective was to apply existing equations in the current population and to compare them with the equation proposed in this work. 2. Subjects and methods The sample size was 694 white adults (429 women and 265 men), aged 18e80 years old (mean of 40.4 years and SD ± 15.3 years), with a BMI range from 16.9 to 48.5 kg/m2 (mean of 25.7 and SD ± 4.7). Volunteers from the wider area of the city center of Athens were asked to attend our lab. Physical activity level was varying from 1.2 to 3 as estimated by the questionnaire and pedometers. None of the participants had any disease that might affect hydration status or body composition or needed clinical care. The population was randomly divided in two sub samples that did not differ significantly with reference to BMI, FM, age, weight, height, and physical activity. The first cohort consisted of 462 (development cohort) while the second cohort of 232 participants (validation cohort), so that the equations could be respectively formed and validated to the first cohort and validation cohort respectively (Table 1). As it has been suggested by Heyward and Wagner (2004) [7], and frequently used in the literature [4,8], the predictive equations’ methodology includes the separation of the population sample into a 2/3 and 1/3 ratio for the development and the validation cohort respectively. All volunteers were informed about the procedures and the aims of the study and signed a written consent form. The study was approved by the Ethical Committee of Harokopio University and was conducted in accordance with the code of ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans. Body weight and standing height were measured in kilograms and meters in light clothing and with no shoes using a digital scale (Seca 861; Seca Ltd., Vogel and Halke, Hamburg, Germany) with an accuracy of 0.1 kg and a stadiometer (Seca Leicester Height Measure; Seca Ltd., Vogel and Halke, Hamburg, Germany) to the nearest 0.1 cm, respectively. The BMI was calculated as weight (kg) divided by height squared (m2). WC was measured in centimeters using an inelastic plastic tape which was applied in the middle of the area between the lower margin of the last rib and the crest of the ilium at the level of the umbilicus, and hip circumference (HC) at the level of the greater trochanters and pubic symphysis, to the nearest 0.1 cm. All the above procedures were performed by a single, welltrained researcher in the same day for each subject as described elsewhere [7]. All subjects were measured from 8 a.m. to 11 a.m. in a fasting state. Resistance and reactance were measured using the Akern BIA 101 single frequency (50 kHz, 800 mAh) impedance plethysmograph. All subjects were fasted for 12 h and had no fluid consumption for at

least 2 h before the measurement. The subjects were in supine position in a non-conductive area, in light clothing and barefoot as indicated by the manufacturer. Four electrodes were placed on the dorsal surface of the right foot. Prior to electrode placement the skin was cleaned with ethanol at the locations of electrode placement. All measurements were performed in the right side of the subjects' body in the morning by experienced personnel. The validity of the Kyle et al. [9], Segal et al. [10], Deurenberg et al. [11], Haapala et al. [12], Heitmann et al. [8], Jakicic et al. [13], Lohman et al. [14], Stolarczyk et al. [15], Sun et al. [16], Gray et al. [17], Lukaski et al. [18,19], Van Loan et al. [20], Williams et al. [21], was tested and all statistical parameters are shown in Table 2. Normality of continues variables was evaluated through the KolmogoroveSmirnov test. Continuous variables are presented as mean ± standard deviation. Multiple linear regression was used to develop the models for estimating fat free mass and fat mass. In particular, stepwise procedure was used to retain the more significant variables (p value for entering a variable was set to 0.05 and p value for removing a variable was set to 0.10). The variables entered in the initial model were: body weight, height, resistance/height2, BMI. Bland-Altman analysis (bias was defined as the difference of the equation and the reference method and limits of agreement as ±2SD) and Intraclass Correlation Coefficient (ICC) were applied in the validation cohort so as to validate the constructed model using DXA as reference method. Furthermore, Bland e Altman analysis and ICC were applied in the retrieved equations, which were validated to DXA as well. The retrieved equations were validated only for the subjects they could be performed regarding age, sex, and weight status. When less than 10 subjects of our sample fulfilled the inclusion criteria for a retrieved equation, no validation was performed due to the small sample size. Any differences between the development and validation cohorts, methods, bias, and its statistical significance were checked with paired samples t-test against DXA results. The statistical significance was set on P < 0.05. All statistical calculations were performed using the SPSS 21.0 version, software (SPSS Inc, Chicago, IL). 3. Results Development and validation cohorts did not differ significantly at age, fat mass, BMI, and physical activity level. All the characteristics of the groups are shown in Table 1. The multiple regression model in which BIA variables were included as independent variables showed that weight, Rz/Ht2, and Xc/Ht2 were significantly associated with FFM. Particularly, the equation formed from BIA was: FFM ¼ 12.299 þ (0.164 * Wt) þ (7.287 * G) e (0.116 * rz/ ht2) þ (0.365 * xc/ht2) þ (21.570 * Height)

Table 1 Descriptive characteristics. Total

Age (years) Weight (kg) Height (meters) BMI (kg/m2) Fat mass % Fat mass (kg) Fat free mass (kg)

Equation cohort

Validation cohort

n ¼ 694

n ¼ 462

n ¼ 232

40.36 ± 15.221 73.1013 ± 15.65455 1.6841 ± 0.9624 25.7226 ± 4.64206 30.659 ± 10.3254 22.569 ± 10.063 47.245 ± 11.271

40.32 ± 15.225 72.9827 ± 15.28871 1.6826 ± 0.9408 25.7542 ± 4.64787 30.514 ± 10.2157 22.421 ± 9.910 47.294 ± 11.149

40.40 ± 15.244 73.3390 ± 16.39464 1.6870 ± 0.10057 25.6593 ± 4.63983 30.949 ± 10.5583 22.864 ± 10.380 47.146 ± 11.536

p

0.741 0.396 0.453 0.783 0.587 0.527 0.736

Fat mass, fat free mass and Fat mass % as estimated by Dual Energy X-ray Absorptiometry.

Please cite this article as: Kanellakis S et al., Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population, Clinical Nutrition ESPEN, https://doi.org/10.1016/j.clnesp.2020.01.003

S. Kanellakis et al. / Clinical Nutrition ESPEN xxx (xxxx) xxx

3

Table 2 Equations retrieved from the literature. Model

Gender

Model equation

Age

Sample size

Country

Kyle et al., 2001 (Geneva) [9]

Both

18e94 yr

343

Switzerland

Segal et al., 1988 [10]

Females

FFM ¼ 4.104 þ 0.518 height2/resistance þ 0.231 weight þ 0.130 reactance þ 4.229 sex (male ¼ 1, female ¼ 0) FFM ¼ 0.00108 height2 - 0.0209 resistance þ 0.23199 weight  0.06777 age þ 14.59453 FFM ¼ 0.00132 height2  0.04394 resistance þ 0.30520 weight  0.16760 age þ 22.66827 FFM ¼ 12.44 þ 0.34 height2/resistance þ 0.1534 height þ 0.273 weight  0.127 age þ 4.56 sex (male ¼ 1, female ¼ 0) FFM ¼ 128.06 þ 1.85 BMI  0.63 weight þ 1.07 height  0.03 resistance þ 10.0 waist  hip ratio FFM ¼ 0.279 height2/resistance þ 0.245 weight þ 0.231  0.077 age  14.94 FFM ¼ 0.279 height2/resistance þ 0.181 weight þ 0.231 height  0.077 age  14.94 FFM ¼ 2.68 þ 0.20 height2/resistance þ 0.19 weight þ 2.55 ethnicity (Caucasian ¼ 0; AfricanAmerican ¼ 1) þ 0.1157 height FFM ¼ 2.04e0.02 resistance þ 0.19 weight þ 2.63 ethnicity (Caucasian ¼ 0; AfricanAmerican ¼ 1) þ 0.2583 height FFM ¼ 5.49 þ 0.476 height2/resistance þ 0.295 weight FFM ¼ 11.59 þ 0.493 height2/resistance þ 0.141 weight FFM ¼ 6.34 þ 0.474 height2/resistance þ 0.180 weight FFM ¼ 5.32 þ 0.485 height2/resistance þ 0.338 weight FFM ¼ 4.51 þ 0.549 height2/resistance þ 0.163 weight þ 0.092 reactance FFM ¼ 11.41 þ 0.600 height2/resistance þ 0.186 weight þ 0.226 reactance FFM ¼ 20.05e0.04904 resistance þ 0.001254 height 2 þ 0.1555 weight þ 0.1417 reactance  0.0833 age FFM ¼ 9.53 þ 0.69 height2/resistance þ 0.17 weight þ 0.02 resistance FFM ¼ 10.68 þ 0.65 height2/resistance þ 0.26 weight þ 0.02 resistance 0.00151 height2  0.0344 resistance þ 0.140 weight  0.158 age þ 20.387 0.00139 height2  0.0801 resistance þ 0.187 weight þ 39.830 0.821 height2/resistance þ 4.97 0.827 height2/resistance þ 5.21 0.53 height2/resistance þ 0.29 weight þ 1.38 sex þ 4.40 (sex: male ¼ 1, female ¼ 0) FFM ¼ 0.734 height2/resistance þ 0.116 weight þ 0.096 reactance þ 0.878 sex - 4.03 (sex: male ¼ 1, female ¼ 0) FFM ¼ 0.54 height2/resistance þ 0.13 weight þ 0.13 reactance - 0.11 age þ 8.71 FFM ¼ 0.37 height2/resistance þ 0.16 weight þ 11.94

17e62 yr

498

USA

Males Deurenberg et al., 1991 [11]

Both

Haapala et al., 2002 [12]

Elderly females

Heitmann 1990 [8]

Males Females

Jakicic et al., 1998 [13]

Overweight females

Overweight females

Lohman 1992 [14]

Females Females Females Males Males Males

Stolarczyk et al., 1994 [15]

Females

Sun et al., 2003 [16]

Females Males

Gray et al., 1989 [17]

Females Males

Lukaski et al., 1986 [18] Van Loan et al., 1990 [26]

Females Males Both

Lukaski et al., 1987 [19]

Both

Williams et al., 1995 [21]

Males Females

1069 >16 yr

661

The Netherlands

62e72 yr

93

Finland

35e65 yr

72

Denmark

67 25e45 yr

123

USA

18e29 30e49 50e70 18e29 30e49

153 122 72 153 111

USA

yr yr yr yr yr

50e70 yr

74

18e60 yr

95

Mexico

12e94 yr

1095

USA

734 19e74 yr

62

USA

25 18e50 yr 18e32 yr

67 47 150

USA USA

19e50 yr

151

USA

49e80 yr

25

USA

23

R, resistance; Ht2/R, height2/resistance, Xc, reactance; height in cm, weight in kg, resistance in ohm, reactance in ohm. All subjects are Caucasian, except Stolarczyk et al. (Native American), and Sun (Caucasian and African-American).

FFM ¼ fat free mass (Kg); Wt ¼ weight (Kg); rz ¼ resistance (Ohm); xz ¼ reactance (Ohm); Ht ¼ height (m), G ¼ gender (0: female and 1: male). No strong correlation was observed among the independent variables. Moreover, this equation explained 94.4% of the total variance of FFM (R2 ¼ 0.944, p < 0.0001, and S.E.E ¼ 2.65). Then, this equation was applied to the validation cohort and the Bland Altman technique showed that the bias of the formed equation was not statistically significant (0.069 Kg, p ¼ 0.707). The limits of agreement were found to be ±5.642 (SD from the mean is ±2.821 Kg) indicating an acceptable validity. Moreover, no statistically significant correlation was observed between average and difference (p ¼ 0.055, r ¼ 0.129). Finally, the equation formed was validated separately in both genders, in different age, BMI and physical activity levels and was found to have no significant bias and high ICC in all subgroups as shown on Table 3.

Table 3 Validation of equation according to gender, BMI, age and PAL. Model

Sample size

HBCS BIA model Gender Females 145 Males 87 BMI NW/OW 196 OB 36 Age 18e39 y 129 40 y 103 PAL <1.69 167 1,7e1.99 39 >2 26

Bias [%BF]

Sig. (2 tailed)

Limits of agreement [%BF]

ICC

0.847 0.176

0.669 0.654

4.764 7.286

0.947 0.909

0.116 0.131

0.568 0.811

5.700 6.548

0.983 0.981

0.389 0.219

0.160 0.393

6.252 5.190

0.980 0.987

0.087 0.516 1.247

0.692 0.261 0.194

5.604 5.108 8.496

0.984 0.989 0.963

Bias and limits of agreement are expressed in kg of fat free mass. HBCS: Hellenic body composition study; NW: Normal weight; OW: Overweight; OB: obesity; PAL: physical activity level; ICC: intraclass correlation coefficient.

Please cite this article as: Kanellakis S et al., Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population, Clinical Nutrition ESPEN, https://doi.org/10.1016/j.clnesp.2020.01.003

4

S. Kanellakis et al. / Clinical Nutrition ESPEN xxx (xxxx) xxx

Table 4 Validation of models. Model

Age (y)

Sample size

Gender

N

Bias (FFM kg)

Sig.

Limits of agreement (FFM kg)

r

pr

ICC

Kyle et al., 2001 (Geneva) [9] Kyle et al., 2001 (Geneva) [9] Segal et al., 1988 [10] Segal et al., 1988 [10] Deurenberg et al., 1990 [11] Deurenberg et al., 1991 [11] Deurenberg et al., 1991 [11] Haapala et al., 2002 [12] Heitmann 1990 [8] Heitmann 1990 [8] Jakicic et al., 1998 [13]

18e94 18e94 17e62 17e62 60e83 >16 >16 62e72 35e65 35e65 25e45

141 202 498 1069 37 661

145 86 145 86 22 145 86 19 77 30 14

2.035 0.553 3.596 2.358 5.862 0.808 0.027 1.106 4.211 2.324 3.695

<0.001 0.14 <0.001 <0.001 <0.001 0.001 0.945 0.051 <0.001 0.001 0.003

5.204 6.884 5.048 8.226 5.434 5.784 7.292 4.602 4.540 6.670 7.410

0.079 0.102 0.022 0.373 0.294 0.238 0.198 0.003 0.002 0.289 0.539

0.343 0.349 0.793 <0.001 0.184 0.004 0.067 0.991 0.986 0.121 0.047

0.932 0.942 0.938 0.929 0.897 0.929 0.938 0.947 0.954 0.953 0.885

Jakicic et al., 1998 [13]

25e45

14

5.567

<0.001

7.362

0.528

0.052

0.888

Lohman 1992 [14] Lohman 1992 [14] Lohman 1992 [14] Lohman 1992 [14] Lohman 1992 [14] Lohman 1992 [14] Stolarczyk et al., 1994 [15] Sun et al., 2003 [16] Sun et al., 2003 [16] Gray et al., 1989 [17] Gray et al., 1989 [17] Lukaski et al., 1986 [18] Lukaski et al., 1986 [18] Van Loan 1990 [26] Van Loan 1990 [26] Lukaski et al., 1987 [19] Lukaski et al., 1987 [19] Williams et al., 1995 [21] Williams et al., 1995 [21] HBCS BIA

18e29 30e49 50e70 18e29 30e49 50e70 18e60 12e94 12e94 19e74 19e74 18e50 18e50 18e32 18e32 19e50 19e50 49e80 49e80 18e80

Females Males Females Males Elderly females Females Males Elderly females Females Males Overweight females Overweight females Females Females Females Males Males Males Females Females Males Females Males Females Males Females Males Females Males Females Males Females and Males

41 51 53 33 32 21 145 145 86 145 86 96 68 50 41 96 68 54 22 232

4.870 2.518 0.964 3.630 1.178 3.947 1.155 4.828 3.673 2.598 0.195 1.215 0.490 5.686 3.269 1.713 0.045 0.695 3.822 0.069

<0.001 <0.001 0.001 <0.001 0.039 <0.001 <0.001 <0.001 <0.001 <0.001 0.667 <0.001 0.384 <0.001 <0.001 <0.001 0.926 0.020 <0.001 0.707

6.238 5.968 3.904 7.814 6.192 7.888 5.086 4.974 8.696 6.444 8.382 5.772 9.232 6.618 8.252 5.194 7.866 4.268 7.876 5.642

0.075 0.160 0.279 0.282 0.013 0.304 0.139 0.115 0.412 0.294 0.340 0.027 0.278 0.005 0.258 0.081 0.305 0.611 0.030 0.129

0.642 0.261 0.043 0.112 0.946 0.18 0.095 0.169 <0.001 <0.001 0.001 0.791 0.021 0.972 0.104 0.430 0.011 <0.001 0.896 0.055

0.892 0.918 0.954 0.915 0.956 0.927 0.942 0.938 0.923 0.914 0.925 0.918 0.904 0.884 0.919 0.937 0.931 0.933 0.938 0.985

93 67 72 123

153 122 72 153 111 74 95 1095 734 62 25 67 47 75 75 151 25 23 694

R, resistance; Ht2/R, height 2/resistance, Xc, reactance; height in cm, weight in kg, thigh circumference in cm, resistance in ohm, reactance in ohm All subjects are Caucasian, except Stolarczyk et al. (Native American), and Sun (Caucasian and African-American). r, Pearson correlation of difference of estimated and measured FFM and average of FFM; pr, significance of r; Sig, Significance of Bias; ICC, intraclass correlation coefficient; HBCS, Hellenic body composition study.

The equation of the current study was shown to perform better in estimating FFM compared with those retrieved from the literature (Table 4). 4. Discussion The purpose of this study was to develop a broadly applicable prediction equation in order to estimate the fat free mass in Greek population with the use of selected BIA and anthropometric measurements. As far as BIA method is concerned, it is a simple and easy-to-apply method, less susceptible to user's errors, which provides sufficient data regarding body composition. BIA takes into account the response of the whole human body to electrical current by measuring resistance and reactance [22]. In particular, BIA in combination with anthropometric measurements are used to predict the fat mass by a variety of clinical studies [23e25]. An easy-to-apply, non-invasive and low cost equation was designed for the prediction of fat free mass for both females and males and carried no significant bias and acceptable limits of agreement. Additionally, the ICC test performed indicated high reliability. The validation of this equation confirms its alternative utilization for both genders and all age, BMI and physical activity ranges when reference methods of body composition assessment are not applicable. Literature review resulted in the identification of 37 BIA equations applicable to the current population through a range of

characteristics such as age, BMI, sex and race. The depicted data in Table 3 assume that none of the equations retrieved from the literature was specific for all these characteristics at the same time. Consequently, although a wide variety of equations do exist in the literature; their results were not as reliable compared to the BIA equation formed in this study since it has 0.985 intraclass correlation coefficient. Another advantage of the equation developed from this work is its simplicity since only height, weight, resistance, reactance and gender are required for estimating Fat Free Mass. According to our findings, BIA equation derived from the current study appears to be the most accurate for Caucasian Greek population and it is suggested that it could be used in clinical practice and research for use in estimating body composition and probably its changes after intervention programs for both genders and all age, BMI and physical activity ranges. Declaration of Competing Interest The authors declare that they have no competing interests. Acknowledgements This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Please cite this article as: Kanellakis S et al., Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population, Clinical Nutrition ESPEN, https://doi.org/10.1016/j.clnesp.2020.01.003

S. Kanellakis et al. / Clinical Nutrition ESPEN xxx (xxxx) xxx

SK was responsible for designing the protocol, conducting the research protocol, analyzing the data and writing the manuscript. ES was responsible for conducting the research protocol, analyzing the data and writing the manuscript. EK was responsible for recruiting the population sample, analyzing the data and delivering the results. GZ was responsible for recruiting the population sample and delivering the results. AK was responsible for analyzing statistical data and delivering the results. FL was responsible for applying basic anthropometric measurements. MM was responsible for applying basic anthropometric measurements and contributing to the manuscript's composition. AG was responsible for ordering the anthropometric data and their interpretation. FM was responsible for ordering the anthropometric data and their interpretation. YM was responsible for reviewing the research protocol and approved the final manuscript. The authors would like to thank, Eftychia Apostolidou, Loukia Gerakiti, Vladlena Khoudokonenko and Maria Chrysi Andrioti for their contribution in data collection. All authors read and approved the final version of the manuscript. References [1] Padwal R, Leslie DW, Lix ML, Majumdar RS. Relationship among body fat percentage, body mass index, and all-cause mortality. A cohort study Ann Intern Med 2016;164:532e41. [2] Wang J, Thornton JC, Kolesnik S, Pierson Jr RN. Anthropometry in body composition: an overview. Ann N Y Acad Sci 2000;904:317e26. [3] Chumlea WC, Guo SS, Zeller CM, Reo NV, Siervogel RM. Total body water data for white adults 18 to 64 years of age: the Fels longitudinal study. Kidney Int 1999;56(1):244e52. [4] Kanellakis S, Skoufas E, Khudokonenko V, Apostolidou E, Gerakiti L, Andrioti MC, et al. Development and validation of two equations based on anthropometry, estimating body fat for the Greek adult population. Obesity 2017;25(2):408e16. [5] Kontogianni MD, Panagiotakos DB, Skopouli FN. Does body mass index reflect adequately the body fat content in perimenopausal women? Maturitas 2005;51(3):307e13. [6] Kanellakis S, Kourlaba G, Moschonis G, Vandorou A, Manios Y. Development and validation of two equations estimating body composition for overweight and obese postmenopausal women. Maturitas 2010;65(1):64e8. [7] Heyward VH, Wagner DR. Leeds. In: Applied body composition assessment. 2nd ed. Champaign, IL: Human Kinetics; 2004. p. 268. xi.

5

[8] Heitmann BL. Evaluation of body fat estimated from body mass index, skinfolds and impedance: A comparative study. Eur J Clin Nutr 1990;44(11): 831e7. [9] Kyle UG, Genton L, Karsegard L, Slosman DO, Pichard C. Single prediction equation for bioelectrical impedance analysis in adults aged 20e94 years. Nutrition 2001;17(3):248e53. [10] Segal KR, Van Loan M, Fitzgerald PI, Hodgdon JA, Van Itallie TB. Lean body mass estimation by bioelectrical impedance analysis: a four-site cross-validation study. Am J Clin Nutr 1988;47(1):7e14. [11] Deurenberg P, van der Kooij K, Evers P, Hulshof T. Assessment of body composition by bioelectrical impedance in a population aged greater than 60 y. Am J Clin Nutr 1990;51(1):3e6. [12] Haapala I, Hirvonen A, Niskanen L, Uusitupa M, Kroger H, Alhava E, et al. Anthropometry, bioelectrical impedance and dual-energy X-ray absorptiometry in the assessment of body composition in elderly Finnish women. Clin Physiol Funct Imaging 2002;22(6):383e91. [13] Jakicic JM, Wing RR, Lang W. Bioelectrical impedance analysis to assess body composition in obese adult women: the effect of ethnicity. Int J Obes Relat Metab Disord 1998;22(3):243e9. [14] Lohman TG. Advances in body composition assessment. In: Current issues in exercise science. , Champaign, IL: Human Kinetics Books; 1992. p. 150. viii. [15] Stolarczyk LM, Heyward VH, Hicks VL, Baumgartner RN. Predictive accuracy of bioelectrical impedance in estimating body composition of Native American women. Am J Clin Nutr 1994;59(5):964e70. [16] Sun SS, Chumlea WC, Heymsfield SB, Lukaski HC, Schoeller D, Friedl K, et al. Development of bioelectrical impedance analysis prediction equations for body composition with the use of a multicomponent model for use in epidemiologic surveys. Am J Clin Nutr 2003;77(2):331e40. [17] Gray DS, Bray GA, Gemayel N, Kaplan K. Effect of obesity on bioelectrical impedance. Am J Clin Nutr 1989;50(2):255e60. [18] Lukaski HC, Bolonchuk WW, Hall CB, Siders WA. Validation of tetrapolar bioelectrical impedance method to assess human body composition. J Appl Physiol 1985;60(4):1327e32. 1986. [19] Lukaski HC. Methods for the assessment of human body composition: traditional and new. Am J Clin Nutr 1987;46(4):537e56. [20] De Lorenzo A, Bertini I, Candeloro N, lacopino L, Andreoli A, Van Loan MD. Comparison of different techniques to measure body composition in moderately active adolescents. Br J Sports Med 1998;32(3):215e9. [21] Williams DP, Going SB, Milliken LA, Hall MC, Lohman TG. Practical techniques for assessing body composition in middle-aged and older adults. Med Sci Sport Exerc 1995;27(5):776e83. [22] Kuczmarski RJ, Flegal KM, Campbell SM, Johnson CL. Increasing prevalence of overweight among US adults: the National Health and Nutrition Examination Surveys, 1960 to 1991. JAMA 1994;272(3):205e11. [23] Guo SM, Roche AF, Houtkooper L. Fat-free mass in children and young adults predicted from bioelectric impedance and anthropometric variables. Am J Clin Nutr 1989;50(3):435e43. [24] Roubenoff R. Applications of bioelectrical impedance analysis for body composition to epidemiologic studies. Am J Clin Nutr 1996;64(3): 459Se62S. [25] Houtkooper LB, Going SB, Lohman TG, Roche AF, Van Loan M. Bioelectrical impedance estimation of fat-free body mass in children and youth: a crossvalidation study. 1985 J Appl Physiol 1992;72(1):366e73. [26] Loan V. Assessment of fat-free mass in teen-agers: use of TOBEC methodology. Am J Clin Nutr 1990;53(4):586e90.

Please cite this article as: Kanellakis S et al., Development and validation of a bioelectrical impedance prediction equation estimating fat free mass in Greek - Caucasian adult population, Clinical Nutrition ESPEN, https://doi.org/10.1016/j.clnesp.2020.01.003