Estimation Of Total Body Water Research Articles

The association between fluid intake, water balance and body composition

AbstractIntroductionThe increasing prevalence of overweight and obesity has developed into an epidemic public health problem worldwide. In this regard, in the last years several investigations have suggested that water intake and water balance could have important implications for both weight management and body composition. The aim of this study was to analyse the association between fluid intake, water balance and body composition in a sample of healthy young adults from Spain.Material and methodsA total of 358 healthy subjects (121 males; 237 females) aged 18–39 years participated in the current study. The validated questionnaire entitled “The hydration status questionnaire” was used to assess fluid intake, elimination, and water balance. Anthropometric measurements (height, weight and waist circumference) were performed according to the recommendations of the International Standards for Anthropometric Assessment (ISAK). The estimates of total body water (TBW), fat mass (FM) and fat free mass (FFM) were acquired by bioelectrical bioimpedance analysis. Physical activity was estimated through the Short form of the International Physical Activity Questionnaire (IPAQ-SF). Differences in anthropometric and body composition variables were assessed through the ANOVA test and considered significant at p < 0.05.ResultsFluid intake was correlated with body water content in females (r = 0.180, p = 0.006) and males (r = 0.266, p = 0.003). An inverse association between water consumption per weight (ml/kg) with body weight (females (f): r = -0.318, p = 0.000; males (m): r = -0.220, p = 0.015), body fat mass (f: r = -0.320, p = 0.000; m: r = -0.200, p = 0.028), and waist circumference (f: r = -0.237, p = 0.000; m: r = -0.215, p = 0.018) was found. Finally, significant differences in body water content in females according to water balance were observed (p = 0.04).DiscussionHigher fluid intake seems to be related with a better body composition, therefore the improvement of water intake and water balance could be useful in weight management and in the prevention of overweight and obesity in healthy young adults.

Development and validation of impedance-based equations for the prediction of total body water and fat free mass in children aged 8 to 11 years

Introduction et but de l’etude Accuracy of the impedance analysis depends on population-specific prediction equations. The aim of this study was to propose new prediction equations to estimate body composition using impedance analysis for healthy Tunisian children and validate them using the deuterium oxide dilution (D2O) technique. Materiel et methodes The body composition was estimated by the Tanita impedance analyzer. The validity of this system was investigated in 134 school children aged between 8 and 11 years. The validity of other published equations was also tested in our sample. Total body water (TBW) and Fat Free Mass (FFM) were determined using the D 2O technique. Participants were divided equally into development (n = 67) and validation groups (n = 67) to develop prediction equation using linear regression models. Resultats et analyse statistique The comparison between body composition obtained by Tanita system and by D2O technique illustrated a significant difference (P O technique, the impedance analysis underestimates fat mass and overestimates FFM and TBW. The prediction equations for TBW and FFM were developed with sex, age, weight and resistance index as possible predictor variables . The selected equations presented the highest adjusted coefficient of determination (R 2), the lowest standard error of the estimate (SEE) value and the lowest P values. The pure error was 1.263 for the TBW equation and 1.646 for the FFM. The Bland Altman plot illustrated the good level of concordance between the TBW and FFM predicted by the new equations and measured by isotope dilution. Conclusion Our study provides valid prediction equations for estimation of TBW, FFM from impedance analysis measures for Tunisian children. These equations are applicable to children aged between 8 and 11 years.

Development and validation of impedance-based equations for the prediction of total body water and fat-free mass in children aged 8–11 years

Accuracy of impedance analysis depends on population-specific prediction equations. The aim of this study was to propose new prediction equations to estimate body composition using impedance analysis for healthy Tunisian children and validate them using the deuterium oxide dilution (D2O) technique. Body composition was estimated by the Tanita impedance analyzer. The validity of this system was investigated in 134 school children aged between 8 and 11 years. The validity of other published equations was also tested in our sample. Total body water (TBW) and Fat-Free Mass (FFM) were determined using the D2O technique. Participants were divided equally into development (n=67) and validation groups (n=67) to develop prediction equation using linear regression models. The comparison between body composition obtained by Tanita system and by D2O technique illustrated a significant difference (p<0.01). Compared to D2O technique, Tanita impedance analysis underestimates fat mass and overestimates FFM and TBW. The prediction equations for TBW and FFM were developed with sex, age, weight and resistance index as possible predictor variables. The selected equations presented the highest adjusted coefficient of determination (R2), the lowest standard error of the estimate (SEE) value and the lowest p-values. The pure error was 1.263 for the TBW equation and 1.646 for the FFM. The Bland Altman plot illustrated the good level of concordance between the TBW and FFM predicted by the new equations and measured by isotope dilution. Our study provides valid prediction equations for estimation of TBW, FFM from impedance analysis measures for Tunisian children. These equations are applicable to children aged between 8 and 11 years.

A novel method of utilizing skinfolds and bioimpedance for determining body fat percentage via a field-based three-compartment model.

The purpose was to determine if skinfolds (SF) and bioelectrical impedance analysis (BIA) could provide accurate estimates of body volume (BV) and total body water (TBW), respectively, for use in a 3-compartment (3-C) model to estimate percent body fat (BF%) when compared to laboratory derived measures. A sample of sixty-four men (age = 22.9 ± 5.4 years) and 59 women (age = 21.6 ± 4.3 years) participated in the study. Laboratory 3-C (3CLAB) model BF% was determined with underwater weighing for body volume (BV) and bioimpedance spectroscopy for total body water (TBW). The 3-C field (3CFIELD) estimates of BF% included BV from the 7-site SF technique and TBW from hand-to-foot BIA. A significant difference in BF% (p < 0.01) was found between the 3CLAB and 3CFIELD in the entire sample and within the men, but the effect sizes (ES) were small (0.09 and 0.17, respectively). The difference between means was not significant in the women (ES = 0.05, p = 0.332). Compared to the 3CLAB, the total error (TE) ranged 2.2-2.4% for 3CFIELD, 5.7-5.8% for SF, and 4.0-4.6% for BIA. The findings suggest that BV and TBW derived from SF and BIA, respectively, can be used in a 3CFIELD model to increase the accuracy of BF% estimates over SF and BIA alone.

Volume Estimates in Chronic Hemodialysis Patients by the Watson Equation and Bioimpedance Spectroscopy and the Impact on the Kt/Vurea calculation.

Background:Accurate assessment of total body water (TBW) is essential for the evaluation of dialysis adequacy (Kt/Vurea). The Watson formula, which is recommended for the calculation of TBW, was derived in healthy volunteers thereby leading to potentially inaccurate TBW estimates in maintenance hemodialysis recipients. Bioimpedance spectroscopy (BIS) may be a robust alternative for the measurement of TBW in hemodialysis recipients.Objectives:The primary objective of this study was to evaluate the accuracy of Watson formula–derived TBW estimates as compared with TBW measured with BIS. Second, we aimed to identify the anthropometric characteristics that are most likely to generate inaccuracy when using the Watson formula to calculate TBW. Finally, we derived novel anthropometric equations for the more accurate estimation of TBW.Design and Setting:This was a cross-sectional study of prevalent in-center HD patients at St Michael’s Hospital.Patients:One hundred eighty-four hemodialysis patients (109 men and 75 women) were evaluated in this study.Measurements:Anthropometric measurements including weight, height, waist circumference, midarm circumference, and 4-site skinfold (biceps, triceps, subscapular, and suprailiac) thickness were measured; fat mass was measured using the formula by Durnin and Womersley. We measured TBW by BIS using the Body Composition Monitor (Fresenius Medical Care, Bad Homburg, Germany).Methods:We used the Bland-Altman method to calculate the difference between the TBW derived from the Watson method and the BIS. To derive new equations for TBW estimation, Pearson’s correlation coefficients between BIS-TBW (the reference test) and other variables were examined. We used the least squares regression analysis to develop parsimonious equations to predict TBW.Results:TBW values based on the Watson method had a high correlation with BIS-TBW (correlation coefficients = 0.87 and P < .001). Despite the high correlation, the Watson formula overestimated TBW by 5.1 (4.5-5.8) liters and 3.8 (3.0-4.5) liters, in men and women, respectively. Higher fat mass and waist circumference (general and abdominal obesity) were correlated with the greater TBW overestimation by the Watson formula. We created separate equations for men and women based on weight and waist circumference.Limitations:The main limitation of our study was the lack of an external validation for our novel estimating equation. Furthermore, though BIS has been validated against traditional reference standards, our assumption that it represents the “gold standard” for body compartment assessment may be flawed.Conclusions:The Watson formula generally overestimates TBW in chronic dialysis recipients, particularly in patients with the highest waist circumference. Widespread reliance on the Watson formula for derivation of TBW may lead to the underestimation of Kt/Vurea..

Validation of anthropometric and bioelectrical impedance analysis (BIA) equations to predict total body water in a group of Cameroonian preschool children using deuterium dilution method

BackgroundLittle information is available on the validity of anthropometry or impedance-based equations for prediction of total body water (TBW) in African children. This study was designed to validate and develop equations to predict total body water in Cameroonian children.MethodsTBW was measured by deuterium dilution in 102 children between 24 and 60 months of age and compared with the ones predicted by 5 anthropometric and 7 BIA equations. Multiple linear regression analysis was used to develop prediction equations for TBW from anthropometric parameters.ResultsUnacceptable discrepancies in the estimates of TBW at individual level were noted with all the equations tested. The following new anthropometry and BIA equations for the estimation of TBW were respectively developed: TBW = 6.488 + 0.434 × sex − 0.039 × age + 0.670 × weight − 0.081 × MUAC (cm) − 0.372 × BMI (adjusted R2 = 0.71, RMSE = 3.6), and TBW = −6.206 + 0.0037 × height2/Z − 0.041 × age + 0.265 × weight + 0.1214 × height (adjusted R2 = 0.68, RMSE = 1.4). The cross-validation procedures revealed that the predicted values of TBW compared with measured values are accurate at a group level.ConclusionThe current published anthropometric and BIA equations are invalid for the estimation of TBW in Cameroonian preschool children. The newly developed anthropometry or BIA prediction equations are valid for use in Cameroonian children aged 24–60 months.

Suitability of Bioelectrical Based Methods to Assess Water Compartments in Recreational and Elite Athletes

Objective: It is important for highly active individuals to easily and accurately assess their hydration level. Bioelectrical impedance (BIA) can potentially meet these needs but its validity in active individuals is not well established. We aim to validate total body water (TBW), extracellular water (ECW), and intracellular water (ICW) estimates obtained from 50 kHz BIA, bioelectrical impedance spectroscopy (BIS), and BIA-based models against dilution techniques in 2 populations: active adults and elite athletes.Methods: Active males (N = 28, 20–39 years) involved in recreational sports and elite athletes (females: N = 57, 16–35 years; males: N = 127, 16–38 years) participated in this study. TBW and ECW were assessed with deuterium and bromide dilution, respectively. ICW was assessed as their difference. Body water compartments were also assessed by BIA (BIA-101), BIS (model 4200), and BIA-based equations.Results: Small but significant differences were observed between alternative methods and the criterion in all subsamples. In female athletes, r2 > 0.69, r2 > 0.57, and r2 > 0.65 were observed between methods in the TBW, ECW, and ICW estimates. In males, r2 > 0.75, r2 > 0.65, and r2 > 0.68 were found between alternative and reference methods in the TBW, ECW, and ICW estimates, respectively, whereas for male recreational exercisers, r2 > 0.58, r2 > 0.73, and r2 > 0.75 were observed. Pure errors ranged between 0.19 to 3.32 kg for TBW, 0.64 to 1.63 for ECW, and 1.98 to 2.64 in ICW. The highest limits of agreement (LoA) were observed in Van Loan and Mayclin equation and the BIA method, respectively, for TBW and ECW assessment and the lowest LoA were observed in BIS for both TBW and ECW estimates.Conclusions: The higher accuracy of BIS in predicting individual TBW, ECW, and ICW highlights its utility in water assessment of recreational and elite athletes.

Resonant cavity perturbation: a promising new method for the assessment of total body water in children

The accurate measurement of total body water (TBW) in children has important clinical and nutritional applications. Resonant cavity perturbation (RCP) is a new method for estimating TBW. This method measures the dielectric properties of the body which are related to body water. For RCP measurements, each subject lay supine on a bed inside a screened room which acts as a resonant cavity. A network analyser measures the frequencies of two low-order cavity resonances of the room, with electric-field vectors that were respectively vertical and horizontal, the resonant frequency shifts relative to the empty room are then derived. These frequency shifts correlates with TBW. The aims of this present study were to (a) develop TBWRCP predictive equations for children using TBWdil as the criterion method, (b) cross-validate the derived equations, (c) determine precision of the TBWRCP method, and (d) compare the criterion method TBWdil with three methods of estimating TBW: RCP, MFBIS and anthropometry.Predictive equations, independent of sex, were developed with linear regression in a group of 36 children. The relationship between combined RCP frequency shifts and TBWdilution had an r2 = 0.90 and standard error of the estimate (SEE) =1.42 kg. Multiple regression analysis, that included a term for body mass index, only had a small effect on r2 = 0.93 and SEE = 1.25 kg. In vivo TBW precision for the vertical, horizontal and combined frequency modes ranged from 0.7 to 3.4%. Bland–Altman analysis indicated close agreement between the criterion method TBWdil and the three other methods of TBW estimation. Mean differences were TBWRCP(2) = 0.01 ± /− 1.34 kg, TBWMFBIS = 0.45 ± /− 1.35 kg, TBWAnthropometry = 0.29 ± /− 1.29 kg.Currently the RCP method does not significantly improve the prediction of TBW compared to MFBIS and anthropometry in this initial study. However the derived equation was independent of sex and body size had only a small effect.

Estimation of body fluids with bioimpedance spectroscopy: state of the art methods and proposal of novel methods

Determination of body fluids is a useful common practice in determination of disease mechanisms and treatments. Bioimpedance spectroscopy (BIS) methods are non-invasive, inexpensive and rapid alternatives to reference methods such as tracer dilution. However, they are indirect and their robustness and validity are unclear. In this article, state of the art methods are reviewed, their drawbacks identified and new methods are proposed. All methods were tested on a clinical database of patients receiving growth hormone replacement therapy. Results indicated that most BIS methods are similarly accurate (e.g. < 0.5 ± 3.0% mean percentage difference for total body water) for estimation of body fluids. A new model for calculation is proposed that performs equally well for all fluid compartments (total body water, extra- and intracellular water). It is suggested that the main source of error in extracellular water estimation is due to anisotropy, in total body water estimation to the uncertainty associated with intracellular resistivity and in determination of intracellular water a combination of both.

A Temperature-Based Bioimpedance Correction for Water Loss Estimation During Sports.

The amount of total body water (TBW) can be estimated based on bioimpedance measurements of the human body. In sports, TBW estimations are of importance because mild water losses can impair muscular strength and aerobic endurance. Severe water losses can even be life threatening. TBW estimations based on bioimpedance, however, fail during sports because the increased body temperature corrupts bioimpedance measurements. Therefore, this paper proposes a machine learning method that eliminates the effects of increased temperature on bioimpedance and, consequently, reveals the changes in bioimpedance that are due to TBW loss. This is facilitated by utilizing changes in skin and core temperature. The method was evaluated in a study in which bioimpedance, temperature, and TBW loss were recorded every 15 min during a 2-h running workout. The evaluation demonstrated that the proposed method is able to reduce the error of TBW loss estimation by up to 71%, compared to the state of art. In the future, the proposed method in combination with portable bioimpedance devices might facilitate the development of wearable systems for continuous and noninvasive TBW loss monitoring during sports.

Bioimpedance index for measurement of total body water in severely malnourished children: Assessing the effect of nutritional oedema

Restoration of body composition indicates successful management of severe acute malnutrition (SAM). Bioimpedance (BI) index (height(2)/resistance) is used to predict total body water (TBW) but its performance in SAM, especially with oedema, requires further investigation. Children with SAM (mid-arm circumference <11.0cm or weight-for-height <70% of median of NCHS reference and/or nutritional oedema) admitted to Jimma University Hospital were included. Tetrapolar-whole-body impedance (Z), resistance (R) and reactance (Xc) were measured at 50 and 200kHzs. Pre- and post-deuterium dose saliva samples were analysed using isotope-ratio mass spectrometry. TBW was regressed on H(2)/Z. Xc and R were height (H)-indexed, and Xc/H plotted against R/H. Thirty five children (16 non-oedematous and 19 oedematous) with median (interquartile range) age of 42 (26-54) months were studied. Height-for-age z-score (mean±SD) was low in both non-oedematous (-3.9±2.8) and oedematous (-3.6±1.7) children. Oedematous children had lower BI parameters than non-oedematous (p<0.001) and hence higher H(2)/Z for a given amount of TBW. At both 50 and 200kHz, association between H(2)/Z and TBW was stronger in non-oedematous children than oedematous (60% higher coefficient of determination and 20% lower standard error of estimate). Intercepts and regression estimates at 50 and 200kHz were similar, in both oedematous and non-oedematous children. In children with oedematous SAM, BI index was weak in predicting TBW. Moreover, predicted TBWs at 200kHz and 50kHz did not differ and hence BI measurement at 50kHz is still practical for TBW estimation.

Different body fluid volumes measured by single- and multi-frequency bioelectrical impedance analyzers in overweight/obese renal patients.

Bioelectrical impedance analysis (BIA) is an affordable, non-invasive and fast alternative method to assess body composition. The purpose of this study was to compare two different tetrapolar BIA devices for estimating body fluid volumes and body cell mass (BCM) in a clinical setting among patients with kidney failure. All double measurements were performed by multi-frequency (MF) and single-frequency (SF) BIA analyzers: a Body Composition Monitor (Fresenius Medical Care, Germany) and BIA-101 (Akern, Italy), respectively. All procedures were conducted according to the manufacturers' instructions (dedicated electrodes, measurement sites, positions, etc). Total body water (TBW), extracellular water (ECW), intracellular water (ICW) and BCM were compared. The study included 39 chronic kidney disease patients (stage III-V) with a mean age of 45.8 ± 8 years (21 men and 18 women) who had a wide range of BMI [17-34 kg/m2 (mean 26.6 ±5)]. A comparison of results from patients with BMI <25 vs ≥25 revealed a significant discrepancy in measurements between the two BIA devices. Namely, in the group with BMI <25 (n=16) acceptable correlations were obtained in TBW (r 0.99; p<0.01), ICW (0.92; p<0.01), BCM (0.68; p<0.01), and ECW (0.96 p<0.05), but those with BMI ≥25 (n=23) showed a discrepancy (lower correlations) in TBW (r 0.82; p<0.05), ICW (0.78; p<0.05), BCM (0.52; p<0.05), and ECW (0.76; p<0.01). Since estimates of TBW, ICW and BCM by the present BIA devices do not differ in patients with BMI <25, they might be interchangeable. This does not hold true for overweight/obese renal patients.

Estimation of total body water and extracellular water with bioimpedance in athletes: A need for athlete-specific prediction models

Bioelectrical impedance analysis (BIA) equations can predict total body water (TBW) and extracellular water (ECW) in non-athletic healthy populations. This study aimed: a) to develop BIA-based models for TBW and ECW prediction based on dilution methods in a sample of national level athletes; and b) to validate the new models with a cross-validation approach in a separate cohort using dilution methods as criterion. Two hundred and eight highly trained athletes (21.3±5.0 years) were evaluated during their respective competitive seasons. Athletes were randomly split into development (n=139) and validation groups (n=69). The criterion method for TBW was deuterium dilution and for ECW was bromide dilution, where ICW was the respective difference between both. Resistance (R) and reactance (Xc) were obtained with a phase-sensitive 50kHz BIA device and used for the estimation of TBW and ECW. Athletic BIA-based models were developed for TBW and ECW [TBW=0.286+0.195*S(2)/R+0.385*Wt+5.086*Sex; ECW=1.579+0.055*S(2)/R+0.127*Wt+0.006*S(2)/Xc+0.932*Sex, where sex is 0 if female or 1 if male, Wt is weight (kg), S is stature (cm), and R and Xc are in ohm (Ω)]. Cross validation revealed R(2) of 0.91 for TBW and R(2) 0.70 for ECW and no mean bias. The new equations can be considered valid, with no observed bias, thus affording practical means to quantify TBW and ECW in national level athletes.

Evaluation of simple body composition methods: assessment of validity in prepubertal Chilean children.

The aim of this study was to assess the validity of body fatness estimations based on skinfolds and bioelectrical iImpedance analyses (BIA) measurements compared to a three-component model (3C model) in prepubertal Chilean children, considering potential differences by sex and nutritional status. Four hundred and twenty four Chilean children (198 females and 226 males) were assessed for body composition. Body fat percentage (BF%) was evaluated by Skinfold equations (Slaughter, Ramirez and Huang) and Bioelectrical impedance (BIA: Tanita BC-418MA) using both the equipment and the Ramirez equation. Measurements based on a 3C model constructed from total body water estimates by isotope dilution and from body volume estimates by air displacement plethysmography were used as gold standard. Coefficient of determination (R2) values were higher in overweight and in the whole group of both gender. All slopes were differed significantly from 1, and most intercepts were significantly different from 0. Skinfold Equations: an underestimation of BF% was found for all equations, being higher with the Slaughter equation. BIA: Tanita underestimated BF% in all groups, whereas Ramirez equation shows an overestimation. Skinfolds and bio-impedance equations serve well to rank children according to their BF%. However, these methods are not accurate for describing body composition in prepubertal Chilean children.

Utility of multi‐frequency bioelectrical impedance compared to deuterium dilution for assessment of total body water

AbstractAimMulti‐frequency bioelectrical impedance analysis (MF‐BIA) may provide a quick, cost‐efficient method of total body water (TBW) assessment. We compared TBW estimates from the Biospace InBody 520, 720, and S10 MF‐BIA devices to TBW estimates from isotopic deuterium dilution (D2O).MethodsTBW was measured in 25 men and 25 women, 18–49 years, 73.6 ± 15.4 kg on each of the three devices and from D2O analysis.ResultsAll MF‐BIA devices significantly overestimated TBW compared to D2O TBW for men (4.7–5.4 kg, 10.8–12.4%; P &lt; 0.01) and women (3.7–4.3 kg, 12.3–14.3%; P &lt; 0.01). Regression analyses in men revealed R2 (0.86–0.90) and SEE (1.7–2.0 kg), and in women revealed R2 (0.82–0.86) and SEE (1.5–1.6 kg). Bland and Altman analyses revealed similar limits of agreement for men (3.5–3.9 kg) and women (3.4–3.7 kg).ConclusionsThe Biospace InBody devices significantly overestimate TBW in men and women. The consistent bias for men and the increasing bias with increasing TBW for women may indicate that these devices are suitable for group TBW estimates in men only.

Influence of posture and frequency modes in total body water estimation using bioelectrical impedance spectroscopy in boys and adult males.

The aim of the study was to examine differences in total body water (TBW) measured using single-frequency (SF) and multi-frequency (MF) modes of bioelectrical impedance spectroscopy (BIS) in children and adults measured in different postures using the deuterium (2H) dilution technique as the reference. Twenty-three boys and 26 adult males underwent assessment of TBW using the dilution technique and BIS measured in supine and standing positions using two frequencies of the SF mode (50 kHz and 100 kHz) and the MF mode. While TBW estimated from the MF mode was comparable, extra-cellular fluid (ECF) and intra-cellular fluid (ICF) values differed significantly (p < 0.01) between the different postures in both groups. In addition, while estimated TBW in adult males using the MF mode was significantly (p < 0.01) greater than the result from the dilution technique, TBW estimated using the SF mode and prediction equation was significantly (p < 0.01) lower in boys. Measurement posture may not affect estimation of TBW in boys and adult males, however, body fluid shifts may still occur. In addition, technical factors, including selection of prediction equation, may be important when TBW is estimated from measured impedance.

Bioimpedance And Dxa Total Body Water Estimations In The Elderly

Bioimpedance techniques have the ability to estimate total body water (TBW) and include single frequency bioimpedance (BIA), bioimpedance spectroscopy (BIS), and multiple-frequency bioimpedance (MFBIA). In addition, dual-energy X-ray absorptiometry (DXA) can predict TBW by using fat-free mass and a constant hydration status of 0.737%. However, the validity of the aforementioned methods has not been established in a healthy elderly population. PURPOSE: Compare BIA, BIS, MFBIA, and DXA TBW estimations in elderly men and women to a criterion deuterium oxide (D2O) TBW measurement. METHODS: Thirty-four women and twenty-four men over the age of sixty-five participated in the study (71 +/5yr, 68.8 +/12.0kg, 167.0 +/8.5 cm). Subjects reported to the lab in a fasted state and provided a urine sample before ingesting approximately 11 grams of D2O. Four hours later the subjects provided another urine sample for the calculation of TBW using a standard isotope dilution method. During the four hour equilibration period the subjects had TBW measured using BIA, MFBIA, BIS, and DXA in no particular order. RESULTS: For men, all methods produced similar and high r values (0.890.95) as well as low standard error of the estimate (SEE) values (1.26-1.52 L) with BIA producing the only nonsignificant mean difference (0.29 L, p=0.31). The MFBIA produced the largest mean difference between D2O and over predicted TBW by 3.43 L. DXA and BIS also both significantly over predicted TBW with mean differences of 1.74 and 2.10 L respectively (p<0.001). For women, all methods produced nearly identical and high r values (0.90-0.91) as well as low standard error of the estimate (SEE) values (0.94-1.02 L). All methods significantly (p<0.001) over estimated TBW, but mean differences were low for DXA (0.92 L) and BIA (0.89 L) compared to BIS (2.37 L) and MFBIA (2.47 L). CONCLUSIONS: The added frequencies used in the MFBIA and the complex Cole models of the BIS did not increase the validity of TBW estimation in elderly men and women as the BIA outperform both devices and uses a single frequency of 50 kHz. However, all methods demonstrated high r values and low SEE values and have the potential to accurately estimate TBW in the current population. However, based on the current results the BIA method used in the current study resulted in the most valid estimations of TBW for elderly men and women compared to D2O.

Total Body Water Estimations Using Bioimpedance in the Athletic Young Adults

Bioimpedance techniques have the ability to estimate total body water (TBW) using a single frequency prediction equation (BIA), using hundreds of frequencies in complex Cole models (BIS), as well as using multiple-frequencies and prediction equations (MFBIA). However, the ability of the above methods to estimate TBW in athletic populations has not been investigated. PURPOSE: Compare BIA, BIS, and MFBIA estimations in athletic males and females to a criterion deuterium oxide (D2O) TBW measurement. METHODS: Twenty-seven females and fifty-one males between the ages of 14 and 30 participated in the study (19.15 +/3.42yr, 66.50+/11.26kg, 172.94+/9.28cm). Subjects reported to the lab in a fasted and hydrated state and provided a urine sample before ingesting approximately 11 grams of D2O. Four hours later the subjects provided another urine sample for the calculation of TBW using a standard isotope dilution method. During the four hour equilibration period TBW was measured using BIA, MFBIA, and BIS in no particular order. RESULTS: For males, all methods produced nearly identical and high r values (0.869-0.878) as well as low standard error of the estimate (SEE) values (2.96-3.06 L) with BIA producing the only significant mean difference (2.66 L, p 0.05). For females, all methods produced similar and high r values (0.82-0.85) as well as nearly identical and low standard error of the estimate (SEE) values (1.31-1.42 L). BIS significantly (p = 0.041) under estimated TBW (0.793 L) while BIA (0.737 L) and MFBIA (1.27 L) significantly (p < 0.02) over estimated TBW compared to D2O. However, BIS and BIA mean difference, although significant, were less than 1 L. CONCLUSIONS: The added frequencies and complex Cole models of the BIS appeared to improve the validity of TBW estimations compared to D2O in athletic males and females ages 14-30 years. However, all methods demonstrated high r values and low SEE values and have the potential to accurately estimate TBW in the current population. However, based on the current results the BIS method used in the current study demonstrated the most valid estimations of TBW for athletic males and females compared to D2O.

Re: Effects of Resistance Versus Multicomponent Training on Body Composition and Functional Fitness in Institutionalized Elderly Women

To the Editor: We read with great interest the study by Sousa and Mendes,1 who reported that 12 weeks of training protocol was not enough to induce changes in the body composition of institutionalized elderly women. The results of that study are particularly important because body composition changes with aging even in weight-stable elderly men and women.2 Beyond these, we would like to comment on some points. Body composition measurement in the study was made using bioelectrical impedance analysis (BIA). For body composition analysis in elderly adults, accuracy of BIA is under discussion.3 The theory of BIA measurement relies on the capacity of hydrated tissues to conduct electrical energy, which allows estimation of total body water (TBW). Calculation of lipid and fat-free mass with BIA was made using equations on TBW,4 so changes in TBW may easily affect BIA results, and pretest preparation is mandatory to minimize the effect of the confounders. The pretest protocol was not reported. Moreover, a recent study showed that a 12-week training program had a significant effect on changes in body fat, total lean mass, and total fat mass in an elderly population.5 In Sousa and Mendes's study, body composition was measured using dual-energy X-ray absorptiometry, which is the recommended alternative to criterion standard methods. We believe that these problems may have affected the results. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: Umut Safer and Vildan Binay Safer discussed and prepared the manuscript. Sponsor's Role: None.

Development and validation of bioelectrical impedance analysis equations for predicting total body water and fat-free mass in North-African adults

Accuracy of the bioelectrical impedance analysis (BIA) depends on population-specific prediction equations. The aim of our study was to develop prediction equations for assessing total body water (TBW) and fat-free mass (FFM) in healthy North-African adults. In all, 250 participants (194 women, 56 men) aged 18-64 years were included in the analysis. BIA variables were measured by a tetra-polar device. TBW and FFM were assessed by the dilution of deuterium (D2O). The participants were sorted by gender and randomly split into development and validation subgroups. The validity of other published equations was also tested using Bland and Altman procedure, proportional bias and pure error. The prediction equations derived were: TBW (l)=5.68+0.267 height(2)/resistance+4.42 sex (male=1, female=0) + 0.225 weight-0.052 age (R(2)=0.92, root mean square error (RMSE)=1.75 l, RMSE%=5.65); and FFM (kg)=7.47 + 0.366 height(2)/resistance+6.04 sex + 0.306 weight-0.063 age (R(2)=0.92, RMSE=2.38 kg, RMSE%=5.61). The new equations provided nonsignificant proportional bias values, and better agreement than other tested equations. Bias and pure error values were 0.36 and 1.88 l for men and 0.00 and 1.82 l for women, for TBW equation. For FFM equation, bias values were 0.43 and -0.04 kg, and pure errors were 2.57 and 2.46 kg for men and women, respectively. The new prediction equations provide reliable estimates of TBW and FFM in North-African adults and are recommended for use in these populations.