Predicting fat-free mass in children using bioimpedance analysis

Body composition assessment is a useful procedure for the study of nutritional status and water distribution. In adults, it is a predictor of morbidity and mortality, since body fatness is associated with risk factors for cardiovascular disease. Bioelectric impedance analysis (BIA) is a simple, safe, and inexpensive method for assessment of body composition both in pediatric and adult subjects. The aim of our study was to validate the impedance index, ZI (H(2)/Z, height in cm(2)/impedance), as a predictor factor of fatfree mass (FFM) and fat mass (FM) in a sample ( n=75) of normal children. Dual-energy X-ray absorptiometry (DXA) was chosen as reference method. Despite some minor bias, DXAis considerably less expensive and easier to administer in pediatric subjects than other established gold standard reference methods for assessing body composition. ZI values were highly correlated with FFM measured with DXA. The following equations were obtained from the regression analysis: (a). male subjects, FFM(DXA)=0.6375 (ZI)+5.9913, r(2)=0.897, p<0.0001; (b). female subjects, FFM(DXA)=0.7597 (ZI)+ 3.5853, r(2)=0.903, p<0.0001. These data support the notion that BIA alone can be used as a surrogate to measure FFM in a pediatric sample.     

Comparison of dual-energy X-ray absorptiometry to four other methods to determine body composition in underweight patients with chronic gastrointestinal disease

Assessment of body composition may provide important information about the nutritional status. The applicability of two safe and convenient methods for body composition analysis, bioelectrical impedance analysis (BIA) and dual-energy x-ray absorptiometry (DXA), in underweight patients with chronic gastrointestinal disease has been sparsely elucidated. Our objective was to compare measurements by DXA with four other methods. Furthermore, we compared total body water (TBW) by BIA using three different BIA equations with measurement of TBW by tritium dilution (TBW-3H2O). Nineteen clinically stable underweight patients with chronic gastrointestinal disease were included in the study (body mass index [BMI], 19.3 +/- 1.2 kg/m2). Body composition was assessed using total body potassium (TBK), isotope dilution of tritium (3H2O), anthropometry (skinfold thickness [SF]), BIA, and DXA. Fat-free mass (FFM) by DXA was in reasonable agreement with body composition measurements by TBK (mean difference(TBK-DXA) = -1.61 kg, r = .88, standard error of the estimate [SEE] = 4.66 kg) and 3H2O (mean difference(3H2O-DXA) = 0.98 kg, r = .93, SEE = 3.34 kg). Although mean values for FFM by DXA differed significantly versus BIA and SF, we found highly significant correlations between the measurements (r = .97 and r = .97, respectively). The mean TBW by BIA was overestimated by 1.9 and 3.1 L compared with TBW-3H2O when prediction equations for normal-weight subjects were used. We conclude that the DXA method is a valuable addition to the list of methods available for body composition studies in clinically stable underweight patients. Our data show that BIA equations for normal-weight subjects overestimated TBW in the patients studied.     

Validation of a leg-to-leg bioimpedance analysis system in assessing body composition in postmenopausal women

OBJECTIVES: To evaluate the validity of a leg-to-leg bioimpedance analysis (BIA) system in predicting body composition as measured by dual-energy X-ray absorptiometry (DXA) in postmenopausal women. SUBJECTS AND METHODS: Body fat mass (FM), %Fat and fat free mass (FFM) were measured in 124 postmenopausal women (age: 51-63 y, body mass index (BMI): 17-38 kg/m2) first by the leg-to-leg BIA system, and then by DXA as reference method. Bland-Altman analysis was used to determine the bias and 95% limits of agreement between the two methods for the assessment of the individual. Precision error (CV%) of the BIA system was obtained by repeated measurements with intermediate repositioning. RESULTS: The leg-to-leg BIA system had a high reproducibility with within-day CVs being 0.6% for FFM and 1.1% for FM, and between-day CVs about twice that. The impedance index (Ht2/Z) obtained by the leg-to-leg BIA was moderately correlated to FFM measured by DXA (r=0.66). A significant, systematic bias was observed between the two methods. The BIA system overestimated FM by a mean of 3.1 kg, and underestimated FFM by 2.7 kg. The analysis of 95% limits of agreement showed that for most individuals, %Fat estimated by the BIA might differ from that measured by DXA by 12% below to 45% above, indicating the lack of agreement between the two methods for the assessment of the individual. CONCLUSIONS: The leg-to-leg BIA system can provide simple, rapid and highly reproducible measurements of body composition for groups, but it has limited accuracy for the assessment of the individual. Population-specific equations will be needed to improve its accuracy in estimating body composition in postmenopausal women.     

Foot-to-foot bioelectrical impedance analysis: a valuable tool for the measurement of body composition in children.

OBJECTIVE: To determine the accuracy of foot-to-foot bioelectrical impedance analysis (BIA) and anthropometric indices as measures of body composition in children. DESIGN: Comparison of foot-to-foot BIA and anthropometry to dual-energy X-ray absorptiometry (DEXA)-derived body composition in a multi-ethnic group of children. SUBJECTS:: Eighty-two European, NZ Maori and Pacific Island children aged 4.9-10.9 y. MEASUREMENTS: DEXA body composition, foot-to-foot bioelectrical impedance, height, weight, hip and waist measurements. RESULTS: Using a BIA prediction equation derived from our study population we found a high correlation between DEXA and BIA in the estimation of fat-free mass (FFM), fat mass (FM) and percentage body fat (PBF) (r=0.98, 0.98 and 0.94, respectively). BIA-FFM underestimated DEXA-FFM by a mean of 0.75 kg, BIA-FM overestimated DEXA-FM by a mean of 1.02 kg and BIA-PBF overestimated DEXA-PBF by a mean of 2.53%. The correlation between six anthropometric indices (body mass index (BMI), ponderal index, Chinn's weight-for-height index, BMI standard deviation score, weight-for-length index and Cole's weight-for-height index) and DEXA were also examined. The correlation of these indices with PBF was remarkably similar (r=0.85-0.87), more variable with FM (r=0.77-0.94) and poor with FFM (r=0.41-0.75). CONCLUSIONS: BIA correlated better than anthropometric indices in the estimation of FFM, FM and PBF. Foot-to-foot BIA is an accurate technique in the measurement of body composition.     

Body composition analysis by leg-to-leg bioelectrical impedance and dual-energy X-ray absorptiometry in non-obese and obese individuals

Aim: The aim of this study is to compare total weight, % body fat (% BF), fat mass (FM) and fat‐free mass (FFM) measured by bioelectrical impedance analysis (BIA) and dual‐energy X–ray absorptiometry (DXA). Methods: This cross‐sectional study included 159 women (mean age: 49.1 ± 10.0 years) and 124 men (mean age: 51.4 ± 8.0 years) subdivided according to sex and body mass index (BMI): BMI < 30 kg/m² (66 women and 50 men); BMI 30–35 kg/m² (53 women and 44 men) and BMI ≥ 35 kg/m² (40 women and 30 men). Bioelectrical impedance was performed in the fasting state on a Tanita TBF‐215 leg‐to‐leg analyser (Tanita, Tokyo, Japan). Whole‐body DXA scans were performed on a Hologic QDR 4500 A bone densitometer (Hologic, Bedford, MA, USA). Total weight, % BF, FM and FFM were tested for intermethod differences. Linear regression and correlation analysis was performed. Limits of agreement and Bland–Altman plots were built. Results: DXA‐derived body composition parameters were not significantly different from BIA estimates and were highly correlated (e.g. for FFM, r = 0.82–0.95). In lean individuals, BIA tended to produce lower values for FM and % BF and higher ones for FFM in comparison with DXA. This trend was reversed at BMI > 35 kg/m². The correlations decreased with increasing BMI. The limits of agreement were much better in men than in women and increased with increasing BMI in both sexes. Conclusions: Compared with DXA, the leg‐to‐leg Tanita TBF‐215 analyser accurately assessed body composition in a heterogeneous group of both sexes. In the very obese women (BMI > 35 kg/m²), BIA measurements should be viewed with caution.     

Body composition by hydrometry (deuterium oxide dilution) and bioelectrical impedance in subjects aged >60 y from rural regions of Cuba, Chile and Mexico

BACKGROUND: In Latin American and Caribbean countries such as Chile, Mexico and Cuba, the population over 60 y has increased steadily. In this age group, there is scarce information about body composition, particularly for those living in rural areas. OBJECTIVE: The purpose of this study was to determine body composition in free-living and healthy elderly subjects >60 y from rural areas of Chile, Cuba and Mexico using deuterium oxide dilution and bioelectrical impedance (BIA) and to develop and cross-validate a predictive equation for this group of subjects by BIA for future use as a field technique. SUBJECTS: The study included 133 healthy subjects (73 males and 60 females) >60 y from rural regions of Cuba, Chile and Mexico. MEASUREMENTS: Total body water, body weight, height and other anthropometric and BIA variables (resistance and reactance) were measured. METHODS: Total body water was determined by deuterium oxide dilution, and fat-free mass (FFM)/fat mass were derived from this measurement. The total sample was used in a split-sample internal cross-validation. BIA and other anthropometric variables were integrated to multiple regression model to design the best predictive equation, which was validated in the other sample. ANOVA, multiple regression and Bland and Altman's procedure were used to analyze the data. RESULTS: Body weight, percentage of fat and fat-free mass were lower in the Cuban men and women compared with Chilean and Mexican men and women. The best predictive equation of the FFM was: FFM kg=(-7.71+(H(2)/R x 0.49)+(country or ethnicity x 1.12)+(body weight x 0.27)+(sex x 3.49)+(Xc x 0.13)), where H(2) is height(2) (cm); R is resistance (Omega); country: Chile=1, Mexico=2 and Cuba=3; sex: women=0 and men=1; body weight (kg) and Xc is reactance (Omega). R(2) was 0.944 and the root mean square error (RMSE) was 2.08 kg. The mean+/-s.d. of FFM prediction was 44.2+/-9.2 vs 44.6+/-10.1. The results of cross-validation showed no significant difference with the line of identity, showing that the predicted equation was accurate. The intercept (=-0.32) was not significantly different from zero (P=0.89) and the slope (=1.02) not significantly different from 1.0 (P>0.9). The R(2) was 0.86, RMSE=3.86 kg of FFM and the pure error was 3.83. CONCLUSION: The new BIA equation is accurate, precise and showed good agreement. The use of this equation could improve the estimates of body composition for the elderly population for these regions, as well as enhancing the opportunity to conduct studies in the elderly population from Latin America.     

Measuring body composition in chronic heart failure: a comparison of methods

AIMS: Fat-free mass (FFM) is increasingly recognized as a systemic marker of disease severity in chronic organ failure and is an important target for physiologic and pharmacologic interventions to improve functional status. The aim of this study was therefore to evaluate two clinical methods to assess FFM in patients with chronic heart failure (CHF) using deuterium dilution (DEU) as reference and bromide dilution to assess the ratio between intracellular (ICW) and extracellular water (ECW) as potential confounder. METHODS: Body composition was measured with dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA) and DEU in 22 stable patients from our heart failure outpatient clinic and 24 healthy age matched controls. RESULTS: FFM values measured by DXA and DEU in patients (r = 0.92, SEE: 3.1 kg) and controls (r = 0.99, SEE: 1.3 kg) were strongly related. In both patients and controls, the inter method difference increased with higher values of FFM (DXA overestimating DEU). The ICW/ECW ratio was within the normal range and comparable between the groups. In patients, a highly significant correlation coefficient was found (r = 0.93, SEE 2.1 p = 0.01) between total body water (DEU) and height squared/resistance (Ht2/R). On multiple regression next to Ht2/R, body weight was an independent predictor of FFM(DEU) (r = 0.95, SEE 2.5 kg, p<0.001; TBWdeu = 0.528 Ht2/R + (0.182 weight) + 8.277). CONCLUSION: DXA and DEU are appropriate and interchangeable laboratory methods for assessment of FFM in clinically stable heart failure patients, however, overestimation of FFM(DXA) should be considered. BIA is a suitable clinical alternative for diagnostic purposes.     

Comparison of four bioelectrical impedance analysis formulas in healthy elderly subjects.

BACKGROUND: Changes of body composition occur with aging and influence health status. Thus accurate methods for measuring fat-free mass (FFM) in the elderly are essential. OBJECTIVE: The purpose of this study was to compare FFM obtained by three bioelectrical impedance analysis (BIA) published formulas specific for the elderly and one equation intended for all age groups, with FFM derived from dual-energy X-ray absorptiometry (FFM(DXA)), in healthy elderly subjects. METHODS: Healthy Caucasian subjects over 65 years (106 women, age 75 +/- 6.2, body mass index 25.2 +/- 4.1 and 100 men, age 74.6 +/- 6.6, body mass index 25.8 +/- 3.0) were measured by DXA (Hologic QDR-4500) and BIA (Xitron, 50 kHz). FFM(BIA) was calculated by the published formulas of Deurenberg, Baumgartner, Roubenoff and Kyle and compared to FFM(DXA) by a Bland-Altman analysis. RESULTS: The Deurenberg and Roubenoff BIA formulas underestimated FFM compared to DXA by -7.1 and -2.9 kg in women and -6.7 and -2.3 kg in men, respectively. The Baumgartner formula overestimated FFM by 4.3 kg in women and 1.4 kg in men. The Kyle formula showed differences of 0.0 kg in women and 0.2 kg in men, and the limits of agreement of FFM(BIA (Kyle)) relative to FFM(DXA) were -3.3 and +3.3 kg for women and -3.8 and +4.3 kg for men. CONCLUSION: The Kyle BIA formula accurately predicts FFM in elderly Swiss subjects between 65 and 94 years, with a body mass index of 17 to 34.9 kg/m(2). The other BIA formulas developed especially for the elderly are not valid in this population.     

Measurement of body fat in healthy elderly men: a comparison of methods

BACKGROUND: Nutritional evaluation of elderly people is of great importance. Two-component methods for body composition assessment, such as anthropometry and bioelectrical impedance (BIA), are widely used in clinical practice, but their fundamental assumptions may be invalid in older people. Dual-energy X-ray absorptiometry (DXA) is a relatively new method for reliable and direct measurements of body mass in its three basic components: total body bone mineral content (TBBMC), mineral free lean tissue mass (LTM), and fat. In this study, percent body fat (%BF) estimates from anthropometry and BIA in men of various ages were compared with corresponding measurements by DXA. METHODS: Body fat percentage was estimated in 67 men aged 20-95 by anthropometric measurements (skinfold thickness, body mass index, or BMI), BIA, and DXA. Age-specific equations were used for anthropometry and BIA. Limits of agreement were calculated between DXA and the other methods. RESULTS: The equations based on BMI and BIA systematically overestimated %BF with respect to %BF measured by DXA in people of all ages. Intermethod difference between DXA and skinfold thicknesses was less marked, but in over-80-year-olds %BF predicted by skinfold measurements underestimated %BF measured by DXA. Interindividual and age-related variation in TBBMC and in fat-free mass mineralization could partly explain the intermethod differences found between DXA and the other methods. CONCLUSIONS: Because of practical constraints, anthropometry and BIA are often the only available options for body composition assessment in clinical routine; therefore, further research on the validity and improvement of these methods in older people is indicated.     

Segmental bioelectrical impedance analysis in children aged 8-12 y: 2. The assessment of regional body composition and muscle mass

OBJECTIVES: To investigate the potential of segmental bioelectrical impedance analysis (BIA) for assessing regional composition and muscle mass in children. DESIGN: Strengths of relationships were determined between (a) BIA indices of trunk, limbs or limb segments and (b) segment fat or fat-free mass (FFM) assessed using dual-energy X-ray absorptiometry (DXA); the extent of agreement was established between two independent models, based on DXA and BIA, of limb muscle and adipose tissue (AT) mass. SUBJECTS: Eighteen boys and 19 girls aged 8-12 y. MEASUREMENTS: BIA and anthropometry of trunk, whole limbs, limb segments and defined sections were used to calculate segmental impedance indices and specific resistivities; segment fat and FFM were obtained using DXA; muscle and AT masses of limbs, segments and sections were estimated using DXA and BIA models, and by anthropometry. RESULTS: Segmental BIA indices were significantly related to composition of the segments assessed using DXA; although substantial bias was observed, there was fairly good agreement (low 95% limits of agreement) between the BIA and DXA models of muscle mass and estimates from each were similarly categorised in tertiles, as were estimates of AT. CONCLUSION: Segmental BIA appears to have potential for assessing in children the composition of body segments, as obtained using DXA, and the masses of muscle and AT in whole limbs, limb segments and defined sections.     

Prediction of fat-free mass by bioimpedance analysis in migrant Asian Indian men and women: a cross validation study

BACKGROUND: Bioimpedance analysis (BIA) is a fast and convenient field technique for estimation of total body fat-free mass (FFM). However, bioimpedance-based prediction equations have been developed in predominantly white populations and little information is available on their usefulness in Asian Indian populations. OBJECTIVE: To develop a prediction equation for FFM based on BIA measurements applicable to a migrant population of Asian Indians and to investigate the predictive accuracy of published BIA-based equations in this ethnic group. DESIGN: FFM was measured by dual-energy X-ray absorptiometry in 211 healthy adults (110 men, 101 women; age ranges 19-74 year) of Asian Indian ethnicity and used as the reference measure to develop prediction equations based on single-frequency BIA measurements of resistance and reactance. A cross-validation technique was applied. Predictive accuracy of published BIA-based equations was assessed in this sample. RESULTS: Sex-specific equations developed in the entire group included height2/resistance and body weight as predictors (R2=0.84 and 0.70 and standard errors of estimate of 2.8 and 2.0 kg for males and females, respectively; CV: 6%). Of published equations examined, one predicted FFM satisfactorily in men with nonsignificant bias and may be applicable to Asian Indian populations. None of the published equations tested performed satisfactorily in women. CONCLUSIONS: Bioimpedance-based equations for predicting FFM developed specifically in Asian Indians are recommended for field studies designed to measure body composition of this ethnic group.     

Segmental bioelectrical impedance analysis in children aged 8-12 y: 1. The assessment of whole-body composition

OBJECTIVES: To investigate the potential of segmental bioelectrical impedance analysis (BIA) for estimating whole-body composition in children. DESIGN: Strengths of relationships were determined between indices of impedance or specific resistivities of body segments and reference four-component model (4-CM) assessments of body composition. SUBJECTS: Eighteen boys and 19 girls aged 8-12 y. MEASUREMENTS: Whole-body and segment BIA and anthropometry were used to calculate impedance indices of the whole body and segments and specific resistivities of segments; total body water (TBW), fat-free mass (FFM) and body fat were assessed using the 4-CM. RESULTS: Segmental BIA indices were significantly related to body composition, provided that appropriate comparisons were undertaken for each index: impedance adjusted for unit segment length was better related to TBW and FFM, whereas segment specific resistivity was better related to body fat. Differences between body composition estimates obtained with the 4-CM and predicted using BIA were partly dependent on limb-to-trunk ratios of BIA indices. CONCLUSION: Segmental BIA has potential for providing additional alternative approaches to the assessment of whole-body composition in children: (a) FFM and TBW were best related to impedance adjusted for segment length; (b) body fat was best related to segment specific resistivity; and (c) the relative influences of different segment BIA indices may be utilisable for generating more valid whole-body composition estimates.     

Body size and composition in Polynesians

OBJECTIVES: To compare the relationship between body size and body composition in New Zealanders of Polynesian and European descent and to develop specific regression equations for fat mass for Polynesians. SUBJECTS: 189 Maori (93 males, 96 females), 185 Samoans (88 males, 97 females) and 241 Europeans (89 males, 152 females) aged 20-70 y. MEASUREMENTS: Height, weight, four skinfold thicknesses, bioelectrical impedance analysis (BIA) and dual energy X-ray absorptiometry (DXA). RESULTS: At higher body mass index levels, Polynesians (Maori and Samoans combined) had a significantly higher ratio of lean mass:fat mass compared with Europeans. Four multiple regression equations incorporating resistance and reactance, height and weight, sum of four skinfolds or sum of two skinfolds were developed in two-thirds of the Polynesian participants using DXA fat mass as the dependent variable. In the remaining one-third of participants, the mean difference between fat mass predicted by these equations (r2 range 0.89-0.93) and DXA fat mass ranged from -0. 06 to +0.25 kg (s.d. -3.67 to +3.71 kg). CONCLUSION: At higher BMI levels, Polynesians were significantly leaner than Europeans, implying the need for separate BMI definitions of overweight and obesity for Polynesians. The regression equations using BIA, height and weight or skinfold thicknesses were good predictors of body composition in Polynesians.     

Indirect estimates of body composition are useful for groups but unreliable in individuals

OBJECTIVE: To assess the usefulness of the body mass index (BMI) in identifying individuals classified as overweight or obese based on estimates of body fat percentage (BF%) obtained by the deuterium dilution (BF%DD) method. In addition, to assess the accuracy of bioelectrical impedance analysis (BIA) and skinfold thickness (SFT) measurements in the estimation of body composition of Australians at the individual and group level. DESIGN: Cross-sectional study. SUBJECTS: One hundred and seventeen healthy Australian volunteers of European descent, comprising of 51 males and 66 females, ranging in age from 19 to 77 y. MEASUREMENTS: BMI was calculated from body weight and height. Fat-free mass (FFM) was estimated from measures of total body water (TBW) using deuterium dilution (FFM(DD)), SFT using the equations of Durnin and Womersley (Br J Nutr 1974; 32: 77-97) (FFM(SFT)), and BIA using the equations of Lukaski et al (J Appl Physiol 1986; 60: 1327-1332) (FFM(Lu)), Segal et al (Am J Clin Nutr 1988; 47: 7-14) (FFM(Se)) and Heitmann (Eur J Clin Nutr 1990; 44: 831-837) (FFM(He)). Estimates of fat mass (FM) were calculated as the difference between body weight and FFM, while BF% was calculated by expressing FM as a percentage of body weight. RESULTS: BMI had poor sensitivity and positive predictive value in identifying individuals as being overweight/obese as classified by BF%DD. Furthermore, estimates of FFM (and hence FM) from BIA or SFT could not be used interchangeably with DD, without the risk of considerable error at the individual level. At the group level errors were relatively smaller, though statistically significant. While FFM(SFT) could be corrected by the addition of the bias (1.2 kg in males and 0.8 kg in females), no simple correction was possible with BIA estimates of FFM for any of the equations used. However, an accurate prediction of FFM(DD) was possible from the combination of FFM(He), biceps SFT and mid-arm circumference in both males and females. The bias of this prediction was small (<0.15 kg), statistically non-significant in both sexes, and unrelated to the mean FFM obtained by the two methods. The revision of Heitmann's estimate of FFM using anthropometric variables described in this study had the best sensitivity (79%), specificity (96%) and positive predictive value (92%) in identifying overweight/obese individuals in comparison to the other equations tested. CONCLUSION: BMI was a poor surrogate for body fatness in both males and females. The currently recommended equations for the prediction of body composition from SFT and BIA provided inaccurate estimates of FFM both at the individual and group level as compared to estimates from DD. However, Heitmann's equations, when combined with measures of the biceps SFT and mid-arm circumference, provided better estimates of FFM both at the individual and group level.     

Body composition in prepubertal girls: comparison of six methods

OBJECTIVE: To compare estimates of fat mass (FM), fat-free mass (FFM) and percentage body fat (%fat) by six different methods in prepubertal girls. DESIGN: Cross-sectional study. SUBJECTS: Normal-weight, multi-ethnic, prepubertal girls (age=8.5+/-0.4 y, n=101). MEASUREMENTS: Body composition was measured in each child by anthropometry (skinfold thickness using Slaughter equation), dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), isotope dilution for total body water measurement (TBW), multifrequency bioelectrical impedance spectroscopy (BIS), and total body electrical conductivity (TOBEC). RESULTS: TOBEC and skinfold thickness yielded the lowest values of FM followed by DXA, TBK, TBW and BIS, with BIS giving the highest value of FM. All methods were significantly different for FFM, FM and %fat (P<0.001), except FFM by DXA and TBK. The Bland-Altman limits of agreement among the methods reveal that they are not directly interchangeable for FM, FFM, or %fat. The largest mean difference for FM was between TOBEC and BIS (-2.90 kg), whereas the smallest mean difference was between TOBEC and skinfold thickness (-0.14 kg). For FFM, the largest mean difference was also between TOBEC and BIS (2.83 kg), but the smallest mean difference for FFM was between DXA and TBK (-0.03 kg). For %fat, the mean differences were larger, -10.5% for TOBEC and BIS and+9.7% for skinfold thickness and BIS. The closest two techniques for %fat were TOBEC and skinfold thickness (mean difference of -0.62%) and DXA and TBK (-1.81%). CONCLUSIONS: We found that estimates of body composition in prepubertal 8-y-old girls are highly method-dependent and that the six methods studied (DXA, TBK, TBW, TOBEC, BIS and anthropometry) are not directly interchangeable.     

Sex and age specific prediction formulas for estimating body composition from bioelectrical impedance: a cross-validation study

In 827 male and female subjects, with a large variation in body composition and an age range of 7-83 years, body composition was measured by densitometry, anthropometry and bioelectrical impedance. The relationship between densitometrically determined fat free mass (FFM) with body impedance (R), body weight (W) and body height (H) was analysed, taking age and sex into account. The intercept of the regression equation FFM = a x H2/R + b was found to be age, and (at older ages) sex dependent, increasing from age 7 to age 15, and slowly decreasing after age 16. Therefore the population was subdivided into two age categories, the one 15 years and younger, and the other 16 years and older. Each age category was randomly divided into two groups, A and B. In each age category the developed prediction formula for group A was cross-validated in group B, and vice versa. No statistically and biologically meaningful differences between predicted and measured FFM were observed in either group. Therefore the data of group A and B in each age category were combined. The best fitted prediction formula at ages less than or equal to 15 was: FFM = 0.406 x 10(4) x H2/R + 0.360 W + 5.58 H + 0.56 Sex - 6.48: n = 166, R2 = 0.97, SEE = 1.68 kg (cv% = 4.9 percent); and at ages greater than or equal to 16: FFM = 0.340 x 10(4) x H2/R + 15.34 H + 0.273 W - 0.127 age + 4.56 sex - 12.44: n = 661, R2 = 0.93, SEE = 2.63 kg (cv% = 5.0 percent).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prediction of lean body mass from multifrequency segmental impedance: influence of adiposity

The aim of the study was to determine the influence of adiposity on the relationship between bioelectrical impedance (BIA) measurements of body segments and estimation of body composition by dual-energy X-ray absorptiometry (DXA). Multiple frequencies of whole body and segmental impedances were measured in 68 normal-weight and obese subjects (46 women and 22 men), mean age 37.2+/-14.8 years (range, 18-69). Total and appendicular lean body mass (LBM) assessed by DXA correlated significantly with total and segmental impedance values adjusted for stature in both obese and normal-weight subjects. Best fitting equations for the prediction of appendicular LBM from segmental impedance measurements were derived for the arm and leg with and without the inclusion of adiposity (the percentage of body fat measured by DXA) in the regression models. Best prediction was obtained at low frequency for the arm and high frequency for the leg. Adiposity appears to significantly influence the prediction of leg LBM by BIA. These preliminary observations need further validation to provide an accurate assessment of appendicular LBM assessment by BIA.     

Bioelectrical impedance analysis (BIA) using bipolar foot electrodes in the assessment of body composition in Type 2 diabetes mellitus

The use of bioelectrical impedance analysis (BIA) for determining human body composition is widely accepted as a safe, rapid, and reliable technique. Although this technique has been validated in normal and obese individuals, only limited studies have been done in special populations. The use of BIA for the measurement of body composition in Type 2 (non-insulin dependent) diabetic patients would be of particular interest for both clinical and investigative studies. The aim of this study was to evaluate the validity of a new bipedal BIA device for the measurement of body composition in a population of individuals with Type 2 diabetes mellitus. The body composition of 48 male and 48 female Type 2 subjects was measured by BIA and dual energy X-ray absorptiometry (DXA). The percentage body fat determined by BIA was significantly correlated with % body fat determined by DXA (r = 0.89, p < 0.0001). Agreement analysis showed that BIA consistently overestimated % fat in female diabetic subjects by approximately 5 % and underestimated % fat in male diabetic subjects by approximately 10 % of the predicted value obtained with DXA. These differences were statistically significant but probably of minor clinical relvance. We conclude that BIA measurement by TBF 105 is a useful and reliable technique for measuring body composition in subjects with Type 2 diabetes mellitus. © 1998 John Wiley & Sons, Ltd.     

Maternal body composition at term gestation and birth weight: is there a link?

To assess the relative influence of maternal body composition at late gestation on birth weight, we examined maternal body composition near term (36.50+/-2.67 weeks gestation) in a group of 29 women, aged 20-39 years. The women came to the laboratory after an overnight fast. After anthropometric measurements, bioelectrical impedance analysis (BIA) was performed, determining resistance (R) and reactance (Xc), with a Tefal scale at 50 kHz. Fat mass (FM, kg) and fat-free mass (FFM, kg) were determined with the total body water (TBW) equation of Siri. The correlation between BIA parameters and birth weights was examined by linear regression analysis. All subjects delivered between 37 and 41 weeks' gestation. The mean+/-SD values of the studied parameters were: Xc=490.00+/-77.34 ohm, R=55.71+/-8.71 ohm, FM=24.18+/-6.51 kg, FFM=45.82+/-2.65 kg, maternal weight gain=9.51+/-6.43 kg, birth weight=3.43+/-0.36 kg. A direct significant correlation was found between FFM, maternal weight gain, and birth weight. It is known that in late pregnancy, maternal weight gain over gestation is linked to birth weight. We observed that FFM was the most important maternal body component associated with the newborn weight at term gestation, and we believe that this finding might be elucidated by fluid retention. In fact, resistance seemed to be inversely related to birth weight and we do not overlook the link between resistance and TBW. The implementation of our study could shed more light on the influence of maternal body composition on birth weight.