Measurement of body water by multifrequency bioelectrical impedance spectroscopy in a multiethnic pediatric population.

BACKGROUND: Bioelectrical impedance spectroscopy (BIS) may provide a noninvasive, rapid method for the assessment of total body water (TBW), extracellular water (ECW), and intracellular water (ICW). Few studies, however, have examined the accuracy of BIS in pediatric populations. OBJECTIVE: Our objective was to evaluate the accuracy of BIS for the measurement of TBW, ECW, and ICW in healthy children. DESIGN: Dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), and BIS measurements were performed in 347 children (202 males and 145 females aged 4-18 y). The reference values for TBW, ECW, and ICW were defined by using a DXA+TBK model. BIS values were evaluated by using the method of Bland and Altman. A randomly selected calibration group (n = 231) was used to derive new BIS constants that were tested in the remaining group (n = 116). RESULTS: BIS values were highly correlated with the reference values (r(2) = 0.94-0.97, P < 0.0001), but differences between the BIS and DXA+TBK models for individuals were significant (P < 0.001). Use of new BIS constants reduced the mean differences between the BIS and DXA+TBK models; the SDs of the mean differences were improved (1.8 L for TBW, 1.4 L for ICW, and 1.0 L for ECW) for the total population. CONCLUSIONS: On a population basis, BIS can be calibrated to replace the DXA+TBK model for the assessment of TBW, ECW, and ICW in healthy children. The accuracy of the BIS measurement in individual children may be refined further by using age- and sex-specific adjustments for the BIS calibration constants.     

A new total body potassium method to estimate total body skeletal muscle mass in children

A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TBK); mmol] measured by whole body (40)K counting (WBC) was developed (SM = 0.0082.TBK) and validated in adults in a previous study. It is unknown whether the adult TBK SM prediction model is applicable for pediatric use. The aim of this study was to derive and validate a pediatric TBK SM prediction equation. SM measured by MRI was used as the criterion and TBK was measured by WBC. The protocol was completed in 116 healthy children, 66 males and 50 females, 11.7 +/- 3.5 y (mean +/- SD, range = 5-17 y). A strong linear correlation was observed between TBK and SM (r = 0.984; P < 0.001). The SM:TBK ratio was 0.0071 +/- 0.0008 kg/mmol in the children studied, much lower than the corresponding value of 0.0082 kg/mmol in adults. An empirical SM prediction equation was developed using TBK alone: SM = 0.0085.TBK - 2.83, r(2) = 0.97, SEE = 1.39 kg. Bland-Altman analysis did not disclose a significant bias in the prediction of SM. When biological factors entered along with TBK in the general linear model, another prediction equation was developed: SM = 5.52 + 0.001.TBK (mmol) + 0.081.weight (kg) - 0.049.height (cm) + 0.00004.TBK . height + race (-0.60 for Caucasian, 0.49 for African-American, and 0 for Hispanic). Because the adult TBK SM prediction model is not applicable for pediatric use, this study provides new empirical TBK SM prediction equations that should prove useful for studies on nutrition, growth, and development in children.     

Body composition in patients with short bowel syndrome: an assessment by bioelectric impedance spectroscopy (BIS) and dual-energy absorptiometry (DXA)

OBJECTIVE: To describe body composition in patients with short bowel syndrome (SBS) by using bioelectric impedance spectroscopy (BIS), dual-energy X-ray absorptiometry (DXA) measurements and anthropometrical-derived estimates. SUBJECTS: In all, 19 patients were included, mean age 54 y, range 36-77 (F/M=11/8). Mean BMI was 21.5 kg/m(2). Eight patients were on home parenteral nutrition (HPN). METHODS: Total body water (TBW), intracellular water and extracellular water were assessed by BIS. TBW were derived from DXA. Fat-free mass (FFM) was assessed by BIS and DXA. TBW and FFM were predicted according to an empirical formula. Differences were analysed using the Bland-Altman method. RESULTS: The mean difference between TBW (DXA) and TBW (BIS) was -1.1 l in women and -1.8 l in men. For FFM, the mean difference between FFM (DXA) and FFM (BIS) was -1.7 kg in women and -2.5 kg in men. The mean difference between TBW (DXA) and TBW (BIS) for all patients was -1.2 l and limits of agreement were (-7.80-5.40). Hydration of FFM assessed by BIS gave a mean of 0.75 (0.08). CONCLUSION: The limits of agreement (Bland-Altman) between DXA and BIS were wide, indicating that methods are not interchangeable, which limits its clinical utility. Most of our patients with SBS were maintained in a stable clinical condition within normal limits of body weight and BMI. FFM and TBW did not appear to be altered in ileostomates or those on HPN.     

Comparison of total body chlorine, potassium, and water measurements in children with cystic fibrosis

BACKGROUND: Symptoms of cystic fibrosis (CF) may limit the utility of total body chlorine (TBCl) and total body potassium (TBK) measurements for assessing body fluid compartments of children. OBJECTIVE: This study assessed relations among independent measurements of TBCl, TBK, and total body water (TBW) in children with CF. DESIGN: We compared cross-sectional measurements of TBCl by in vivo neutron activation analysis, TBK by whole-body counting of (40)K, TBW by D(2)O dilution [TBW(D(2)O)], and TBW from TBCl and TBK [TBW(Cl + K)] in 19 prepubertal children (13 boys) aged 7.6-12.5 y who had mild symptoms of CF. Body-composition measurements were compared with data from previous studies of healthy children. RESULTS: Subjects with CF had deficits in TBCl, TBK, TBW, and body weight compared with control reference data (P < 0.05). The ratios (TBCl + TBK)/TBW and TBCl/TBK were not significantly different from control reference values, and plasma chlorine and potassium concentrations were within control reference ranges. The sum of TBCl and TBK correlated with TBW(D(2)O) (r(2) = 0.79, P < 0.001), and TBW(Cl + K) correlated with TBW(D(2)O) (r(2) = 0.78, P < 0.001). TBW(Cl + K) was similar to TBW(D(2)O) (mean +/- SEM: 19.0 +/- 0.5 compared with 19.4 +/- 0.5 L; NS). CONCLUSIONS: Prepubertal children with mild symptoms of CF can develop deficits in TBCl, TBK, and TBW that reflect chronic energy malnutrition. Mild symptoms of CF do not appear to affect normal relations among TBCl, TBK, and TBW. Measurements of TBCl and TBK may be used to assess body fluid compartments in these patients.     

A comparison of four methods of estimating the body composition of male endurance athletes.

Comparisons were effected of the following four methods of estimating the percent body fat (%BF) of 12 highly trained male endurance athletes (mean +/- SD = 2.20 +/- 4.9 years, 176.8 +/- 5.9 cm 64.2 +/- 6.4 kg): underwater weighing (UWW), total body water (TBW), total body potassium (TBK) and dual-energy X-ray absorptiometry (DEXA). The DEXA mean of 6.8% BF was significantly less (P < 0.05) than those estimated via UWW: 9.7% BF; TBW: 10.6% BF (fat-free mass of FFM = 72.0% H2O); and TBK: 9.7% BF (FFM = 66.6 mmol K.kg-1). Nevertheless, the DEXA % BF correlated 0.746 and 0.737 (both P < 0.01) with those from UWW and TBW, respectively; these were the only correlation coefficients to attain statistical significance (P < or = 0.05). Despite the similar means for UWW, TBW and TBK, 12 of the 36 individual differences between these three methods ranged from 3.2 to 10.4% BF. A critical assumption of UWW, which is regarded by many as the criterion method for the estimation of % BF, is that the FFM has a density of 1.100 g.cm-3. Use of in vivo-measured TBW and bone mineral (via DEXA) for the computation of FFM densities for our subjects, while assuming that the two other components of the FFM (protein and non-bone mineral) remained constant, resulted in scores ranging from 1.09541 to 1.10246 g.cm-3 (mean +/- SD = 1.09881 +/- 0.00254 g.cm-3). FFM and % BF differences between use of a constant FFM density of 1.100 g.cm-3 and the individual values ranged from -1.02 to 0.57 kg (mean +/- SD = -0.28 +/- 0.60 kg) and from -0.9 to 1.7% BF (mean +/- SD = 0.5 +/- 0.9% BF), respectively. It may be concluded that with young male athletes: (1) use of constants based on normal male cadavers yielded similar group means for % BF determined by UWW, TBW and TBK but the DEXA % BF correlated significantly with those from UWW and TBW; and (2) in vivo measurements of individual differences in TBW and bone mineral support the use of conventional UWW for the estimation of % BF.     

Total body protein mass: validation of total body potassium prediction model in children and adolescents

Protein is an important body component for monitoring growth, development, and nutritional status. We previously developed a total body potassium (TBK, in mmol) and bone mineral (Mo, in kg) model for predicting total body protein (TBPro, in kg) in adults (TBPro = 0.00252 x TBK + 0.732 x Mo). However, the applicability of the TBK-Mo model for children is unknown. The study aims were to develop a TBK-independent 6-component (6-C) TBPro approach as the criterion, and then to validate the TBK-Mo model in children. The following measurements were made in adolescents and children (n = 62, 38 boys and 24 girls, aged 5-17 y): body weight (BW, in kg), body volume (BV, in liters) by air displacement plethysmography, total body water (TBW, in kg) by 2H2O dilution, Mo by dual-energy X-ray absorptiometry, and TBK by whole-body counting. A 6-C model was derived as TBPro = 2.922 x BW - 0.301 x TBW - 2.039 x Mo - 2.632 x BV. The TBPro estimates did not differ between the 6-C and TBK-Mo models (mean +/- SD, 0.20 +/- 0.86 kg). There was a significant correlation between TBPro by the 6-C and TBK-Mo models (r = 0.94, P < 0.001). Bland-Altman analysis indicated that the differences between TBPro by 6-C and TBK-Mo models were not significantly correlated with the mean TBPro estimates by the 2 models (r = 0.032, P > 0.05). The TBK-Mo model can thus be used to estimate TBPro in healthy adults, adolescents, and children > 5 y old.     

Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models

BACKGROUND: Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings. OBJECTIVE: The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults. DESIGN: SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/m(2)) < 30]. RESULTS: Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht x (0.00744 x CAG(2) + 0.00088 x CTG(2) + 0.00441 x CCG(2)) + 2.4 x sex - 0.048 x age + race + 7.8, where R:(2) = 0.91, P: < 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = -2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 x BW + 7.80 x Ht + 6.6 x sex - 0.098 x age + race - 3.3, where R:(2) = 0.86, P: < 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = -1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic. CONCLUSION: These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults.     

Comparison of isotope dilution with bioimpedance spectroscopy and anthropometry for assessment of body composition in asymptomatic HIV-infected and HIV-uninfected breastfeeding mothers

BACKGROUND: The effect of breastfeeding on the nutrition of HIV-infected (HIV+) mothers is unknown. Simple, valid methods are needed for body-composition assessment of HIV+ women. OBJECTIVE: We compared the ability of bioimpedance spectroscopy (BIS) and anthropometry with that of isotope dilution (2H2O) to measure fat-free mass (FFM) and fat mass (FM) in HIV+ and HIV-uninfected (HIV-) breastfeeding South African mothers. DESIGN: Total body water (TBW) content of 68 lactating mothers (20 HIV+, 48 HIV-) was measured 10 wk after delivery by using BIS and 2H2O to measure FFM and FM. Anthropometric measurements included body mass index (BMI; in kg/m2), midupper arm circumference (MUAC), and 4 skinfold thicknesses. RESULTS: TBW, FFM, and FM measurements determined by BIS were correlated with 2H2O measurements in HIV+ (r = 0.664, 0.621, and 0.872, respectively; P < 0.01) and HIV- (r = 0.876, 0.868, and 0.932, respectively; P < 0.001) mothers. TBW measured by BIS was greater than that measured by the 2H2O method in both HIV+ (1.8 L) and HIV- (1.5 L) women; FM or FFM did not differ significantly by method. BMI, MUAC, and all skinfold-thickness measurements correlated strongly (r > 0.62, P < 0.001) with FM measured by 2H2O in both groups. BMI and MUAC correlated (r > 0.64, P < 0.001) with FFM in HIV- mothers but not in HIV+ mothers. CONCLUSIONS: In HIV+ and HIV- breastfeeding mothers, BIS provides an estimate of body composition comparable to that obtained with the 2H2O method. BMI and MUAC are useful in predicting FM in both groups but are not valid measures of FFM in HIV+ mothers.     

Body composition in the elderly: Total body water and anthropometry

Body composition measured with isotopic dilution was compared with anthropometric measurements. The study was carried out in 47 subjects from both sexes, 65 to 92 years old. Total body water (TBW), anthropometric measurements, and dynamometry were assessed. TBW was significatively higher in men than women and decreased with age. Dynamometry and fatfree mass were well correlated (r=0.73 in males and r=0.58 in females) and significantly different between sexes. A negative correlation was found for dynamometry with age, being significant for women. Linear regression equations to predict TBW from anthropometric measurements in males and females were obtained: Males: TBW(I)=19.349+0.617 weight(kg) — 0.931 mid-arm circumference(cm)+0.122 dynamometry (kg) Females: TBW(l)=−5.531+0.343 weight(kg)-0.213 triceps skinfold (mm)+ 0.148 dynamometry(kg) + 3.424 wrist diameter (cm). This simple model is proposed for use in epidemiological and field studies where other more sophisticated methods can not be applied.     

Appendicular skeletal muscle mass: measurement by dual-photon absorptiometry

Dual-photon absorptiometry (DPA) allows separation of body mass into bone mineral, fat, and fat-free soft tissue. This report evaluates the potential of DPA to isolate appendages of human subjects and to quantify extremity skeletal muscle mass (limb fat-free soft tissue). The method was evaluated in 34 healthy adults who underwent DPA study, anthropometry of the limbs, and estimation of whole-body skeletal muscle by models based on total body potassium (TBK) and nitrogen (TBN) and on fat-free body mass (FFM). DPA appendicular skeletal muscle (22.0 +/- 3.1 kg, mean +/- SD) represented 38.7% of FFM, with similar proportions in males and females. There were strong correlations (all p less than 0.001) between limb muscle mass estimated by DPA and anthropometric limb muscle areas (r = 0.82-0.92), TBK (r = 0.94), and total-body muscle mass based on TBK-FFM (r = 0.82) and TBK-TBN (r = 0.82) models. Appendicular skeletal muscle mass estimated by DPA is thus a potentially practical and accurate method of quantifying human skeletal muscle mass in vivo.     

Body-water compartments measured by bio-electrical impedance spectroscopy in patients with chronic obstructive pulmonary disease

It was previously demonstrated that single frequency bio-electrical impedance (BIA) measurement at 50 kHz is a useful method to assess total body water (TBW) in patients with chronic obstructive pulmonary disease (COPD). In the present study it was examined whether bio-electrical impedance spectroscopy (BIS) could predict extracellular water (ECW) and improve the prediction of TBW in these patients. TBW and ECW (corrected bromide space) were measured by deuterium and bromide dilution. In 37 COPD patients prediction equations were obtained using BIS (5-500 kHz) measurements, and these were cross validated in a second group of 40 COPD patients. All patients were in a clinically stable condition. TBW predicted by BIS was not significantly different from actual TBW and demonstrated a comparable standard error of estimate (SEE) as found previously in healthy subjects (male symbol correlation coefficient: r = 0.88, SEE: 2.3 L, female symbol r = 0.85, SEE: 2.9 L). Predicted ECW using BIS-measurements was not significantly different from measured ECW (male symbol r = 0.75, SEE: 1.4 L, female symbol r = 0.73, SEE: 1.2 L), but the error in the prediction was relatively large and the correlation between predicted and actual ECW relatively low compared to most studies in healthy subjects. Predicted TBW using BIS was comparable to actual TBW, but presented no improvement of the prediction of TBW using BIA at 50 kHz and a patient specific regression equation. The error of the prediction of ECW by BIS limits the ability to predict fluid shifts in individual patients with clinically stable COPD.     

A 3-year longitudinal study on body composition changes in the elderly: role of physical exercise

BACKGROUND: Cross-sectional data have shown that sarcopenia and fat accumulation are associated with aging and can be limited by structured physical training. However, it is often difficult to maintain a long-term compliance to training programs. It is not clear whether leisure-time physical activity is effective in preventing sarcopenia and fat accumulation. OBJECTIVES: (i) To investigate longitudinal body composition changes in a population of elderly people in good apparent health. (ii) To evaluate the impact of leisure-time physical activity on muscle mass and characteristic as reflected by total body potassium per fat-free soft tissue (TBK/FFST), and on fat accumulation. DESIGN: Longitudinal evaluation over 3 years, of body composition changes in 74 healthy men and 66 women, over 65 years old. Body fat and FFST were analyzed by dual-energy X-ray absorptiometry and TBK by whole-body (40)K counter. Physical activity was analyzed by a specific questionnaire. RESULTS: Despite a stable total body weight, FFST and appendicular skeletal muscle mass slightly decreased (-0.3+/-1.4 and -0.2+/-2.2 kg, P<0.01, respectively) as well as the TBK/FFST (-4.1+/-6.3 mmol/kg, P<0.001), over the 3-year period. Body fat increased significantly (0.6+/-2.2 kg, P<0.0001), and it accumulated mainly in the abdomen (0.4+/-1.5 kg, P<0.01). Multiple regression analysis showed that body composition changes were related mainly to body weight changes. Nevertheless, positive linear correlations were observed between the degree of engagement in leisure-time physical activity and FFST (P<0.01), appendicular skeletal muscle mass (P<0.05), TBK/FFST (P<0.05), whereas negative correlation was observed with total and truncal fat (P<0.01). CONCLUSIONS: Mild but significant decline in muscle mass and its TBK content, and body fat accumulation were observed over a 3-year period in healthy elderly subject: leisure-time physical activity does not seem to prevent them. However, a higher level of physical activity is associated with higher muscle mass and TBK content, and less total and truncal fat.     

Body composition in patients with an ileostomy and inflammatory bowel disease: validation of bio-electric impedance spectroscopy (BIS)

OBJECTIVE: To validate bio-electric impedance spectroscopy (BIS) by comparison with other methods for determination of body water compartments in stable subjects with an ileostomy and no or minor small bowel resection for inflammatory bowel disease (IBD). SUBJECTS: Twenty-one subjects were included, age range 36-65 y (female/male=12/9), Crohn's disease (CD), n=14, ulcerative colitis (UC), n=6 and indeterminate colitis (IDC), n=1. METHODS: Fluid compartments were assessed by the use of three independent methods: BIS, dual-energy X-ray absorptiometry (DXA) and dilution techniques (DIL); tritiated water (total body water, TBW); and bromide (extracellular water, ECW), respectively. Intra-cellular water (ICW) was calculated as TBW-ECW. For comparison TBW was also predicted according to an empirical formula. Differences were analysed using Bland-Altman plots. RESULTS: The mean TBW values obtained from the impedance measurement differed in the order of -2.21 (DIL) to 1.41 (DXA) in women and -2.01 (DIL) to 2.61 (DXA) in men, from the measured and derived values of total body water. Prediction of TBW gave values that were close to BIS, with a mean difference of -0.31 in male subjects and +0.51 in female subjects.Assessment of ECW revealed that the mean difference between dilution and impedance was less in women than in men (P<0.01). CONCLUSION: The differences between all methods to assess fluid compartments are pronounced. To further investigate the use of the method in clinical practice for dynamic monitoring of rehydration in ileostomates with acute diarrhoea, repeated measurements together with comparison with weight fluid-balance charts are suggested. SPONSORSHIP: The study was supported by grants from the Swedish Medical Research Council (17X-03117), G?teborgs L?kars?llskap and IB and A Lundbergs forskningsstiftelse.     

Assessment of fat-free mass using bioelectrical impedance measurements of the human body

A method which involves the measurement of bioelectrical resistive impedance (R) for the estimation of human body composition is described. This method is based upon the principle that the electrical conductivity of the fat-free tissue mass (FFM) is far greater than that of fat. Determinations of R were made in 37 healthy men aged 28.8 +/- 7.1 yr (mean +/- SD) using an electrical impedance plethysmograph with a four electrode arrangement that introduces a painless signal (800 microA at 50 kHz) into the body. FFM was assessed by hydrodensitometry and ranged from 44.6-98.1 kg. Total body water (TBW) determined by D2O dilution and total body potassium (TBK) from whole body counting were 50.6 +/- 10.3 L and 167.5 +/- 38.1 g, respectively. Test-retest correlation coefficient was 0.99 for a single R measurement and the reliability coefficient for a single R measurement over 5 days was 0.99. Linear relationships were found between R values and FFM (r = -0.86), TBW (r = -0.86), and TBK (r = -0.79). Significant (p less than 0.01) increases in the correlation coefficients were observed when the predictor Ht2/R was regressed against FFM (r = 0.98), TBW (r = 0.95), AND TBK (r = 0.96). These data indicate that the bioelectrical impedance technique is a reliable and valid approach for the estimation of human body composition. This method is safe, noninvasive, provides rapid measurements, requires little operator skill and subject cooperation, and is portable. Further validation of this method is recommended in subjects with abnormal body composition.     

Validation of a bioelectrical impedance analysis equation to predict appendicular skeletal muscle mass (ASMM)

RATIONALE: Appendicular skeletal muscle mass (ASMM) is useful in the evaluation of nutritional status because it reflects the body muscle protein mass. The purpose of this study was to validate, against dual-energy X-ray absorptiometry (DEXA), a BIA equation to predict ASMM to be used in volunteers and patients. METHOD: Healthy men (n = 246 men, BMI 25.3+/-2.9 kg/m(2)) and women (n =198, 24.1+/-3.6 kg/m(2)), and heart, lung and liver transplant patients (213 men, BMI of 24.6+/-4.4 kg/m(2); 113 women, BMI 23.0+/-5.2 kg/m(2)) were measured by BIA (Xitron Technologies) and DEXA (Hologic QDR 4500). A BIA equation to predict ASMM (kg) that included height(2)/resistance, weight, gender, age and reactance, was developed by means of multiple regressions. [table: see text] Mean difference (Bland-Altman) for volunteers was 0.1+/-1.1 kg, r =0.95, SEE 1.12 kg and for patients -0.4+/-1.5 kg, r =0.91, SEE 1.5 kg.Best fitted multiple regression equation was -4.211 + (0.267 x height2 / resistance) + (0.095 x weight)+(1.909 x sex (men = 1, women = 0)) + (-0.012 x age) + (0.058 x reactance). CONCLUSIONS: BIA permits the prediction of ASMM in healthy volunteers and patients between 22 and 94 years of age. A slightly larger, though clinically not significant, error was noted in patients.     

Whole-body skeletal muscle mass: development and validation of total-body potassium prediction models

BACKGROUND: A substantial proportion of total body potassium (TBK) in humans is found in skeletal muscle (SM), thus affording a means of predicting total-body SM from whole-body counter-measured (40)K. There are now > 30 whole-body counters worldwide that have large cross-sectional and longitudinal TBK databases. OBJECTIVE: We explored 2 SM prediction approaches, one based on the assumption that the ratio of TBK to SM is stable in healthy adults and the other on a multiple regression TBK-SM prediction equation. DESIGN: Healthy subjects aged >or= 20 y were recruited for body-composition evaluation. TBK and SM were measured by whole-body (40)K counting and multislice magnetic resonance imaging, respectively. A conceptual model with empirically derived data was developed to link TBK and adipose tissue-free SM as the ratio of TBK to SM. RESULTS: A total of 300 subjects (139 men and 161 women) of various ethnicities with a mean (+/- SD) body mass index (in kg/m(2)) of 25.1 +/- 5.4 met the study entry criteria. The mean conceptual model-derived TBK-SM ratio was 122 mmol/kg, which was comparable to the measurement-derived TBK-SM ratios in men and women (119.9 +/- 6.7 and 118.7 +/- 8.4 mmol/kg, respectively), although the ratio tended to be lower in subjects aged >or= 70 y. A strong linear correlation was observed between TBK and SM (r = 0.98, P < 0.001), with sex, race, and age as small but significant prediction model covariates. CONCLUSIONS: Two different types of prediction models were developed that provide validated approaches for estimating SM mass from (40)K measurements by whole-body counting. These methods afford an opportunity to predict SM mass from TBK data collected in healthy adults.     

Dual-photon absorptiometry: comparison of bone mineral and soft tissue mass measurements in vivo with established methods

This study extended initial observations that indicated the potential of dualphoton absorptiometry (DPA) to measure total-body bone mineral (TBBM) and fat in vivo. DPA-derived TBBM and fat were compared with established methods in 13 subjects (aged 24-94 y) who underwent measurement of body density (Db), total-body water (TBW), potassium (TBK), calcium (TBCa, delayed-gamma neutron activation), and nitrogen (prompt-gamma neutron activation). TBBM was highly correlated with TBCa (r = 0.95, p less than 0.001) and the slope of TBCa vs TBBM (0.34) was similar to Ca content of ashed skeleton (0.34-0.38). DPA-measured fat (means +/- SD, 16.7 +/- 4.9 kg) correlated significantly (r = 0.79-0.94; p less than 0.01-0.001) with fat established by Db (16.3 +/- 5.4 kg), TBW (16.0 +/- 4.3 kg), TBK (17.7 +/- 4.6 kg), combined TBW-neutron activation (17.6 +/- 5.9 kg), and means of all four methods (16.9 +/- 4.8 kg). DPA thus offers a new opportunity to study human skeleton in vivo and to quantify fat by a method independent from the classical assumption that bone represents a fixed fraction of fat-free body mass.     

Familial resemblance of body composition in prepubertal girls and their biological parents

BACKGROUND: Heritability estimates for body mass index (BMI; in kg/m(2)) in children generally have been derived from twin and adoption studies. However, BMI does not reflect total or regional body composition. OBJECTIVE: We evaluated the familial resemblance of body composition between prepubertal girls of normal weight and body fatness and their parents by using state-of-the-art technology. DESIGN: The subjects were 101 girls [mean age: 8.5 +/- 0.4 y; percentage body fat (%BF): 12-30%] and their biological parents. Weight, height, and body composition [fat mass (FM), fat-free mass (FFM), and %BF] were measured with dual-energy X-ray absorptiometry (DXA) and total body potassium (TBK). RESULTS: Weight, height, and BMI showed low-to-moderate similarity between the girls and both their parents (r = 0.29-0.44, P < 0.01). The girls' FM, FFM, and %BF were significantly related to both parents' body composition. Cross-generational equations were developed for DXA, eg, child's %BF = 12.4 + (0.158 paternal %BF) + (0.145 maternal %BF) (adjusted r(2) = 0.16, P < 0.001). Regional analysis with DXA showed that the adjusted r(2) values for the arm, trunk, and leg regions, respectively, were 0.17, 0.33, and 0.31 for lean tissue mass and 0.11, 0.14, and 0.09 for FM. TBK showed a similar relation between parents and girls (r = 0.28-0.47, P < 0.01). Significant heritability (h(2) +/- SE) was detected for BMI (0.35 +/- 0.17, P = 0.03) and %BF measured with DXA (0.50 +/- 0.12, P = 0.0001). CONCLUSION: The body composition of prepubertal girls of normal weight and body fatness is significantly related to the body composition of both biological parents.     

Combination megestrol acetate, oxandrolone, and dietary advice restores weight in human immunodeficiency virus.

BACKGROUND: We examined changes in total body weight (TBW) and health-related quality of life (HRQL) during prolonged combination weight-gaining therapy and dietary advice in HIV. Design: This was a cohort study of patients initially randomized to single agent therapy for 2 months, megestrol acetate (800 mg daily), or oxandrolone (10 mg twice daily), followed by both agents and dietary advice for 5 months. METHODS: Two community health clinics and 1 urban infectious disease clinic were included, as were HIV-positive adult patients receiving highly active antiretroviral therapy with documented 5% weight loss. TBW and HRQL were measured after 7 months (7 m). RESULTS: Twenty-nine of 39 participants completed 7 m. The average sample age was 40 years, 75% were male, and 52% were of color at enrollment. Baseline mean TBW and body mass index (BMI) were 62.5 kg and 21 kg/m(2), respectively. Net gains in TBW, lean body mass, and fat during the 7 m were 5.3 kg (8.5% of baseline), 2.1 kg, and 3.1 kg, respectively (p < .01 for each). BMI increased to 23.1 kg/m(2) (p < .01). Dietary intake increased by 467 kcal/day (p = .03). Physical health improved by 5.7 (100-point scale, p < .01), and mental health was unchanged (-4.2, p = .11). In multivariable models, female gender (p < .01), lower baseline HIV viral load (p = .03), and increasing age (p < .01) were associated with TBW gain. Injection drug use (p < .01) and higher baseline HIV viral load (p < .01) were associated with reduction in physical health. CONCLUSIONS: Prolonged combination therapy with megestrol acetate, oxandrolone, and dietary advice could reverse weight loss and low BMI associated with incomplete viral suppression and improve physical health.     

Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis

OBJECTIVE: To measure body water distribution and to evaluate the accuracy of eight-polar bioelectrical impedance analysis (BIA) for the assessment of total body water (TBW) and extracellular water (ECW) in severe obesity. DESIGN: Cross-sectional study. SETTING: Obesity clinic. SUBJECTS: In all, 75 women aged 18-66 y, 25 with body mass index (BMI) between 19.1 and 29.9 kg/m(2) (ie not obese), 25 with BMI between 30.0 and 39.9 kg/m(2) (ie class I and II obese), and 25 with BMI between 40.0 and 48.2 kg/m(2) (ie class III obese). METHODS: TBW and ECW were measured by (2)H(2)O and Br dilution. Body resistance (R) was obtained by summing the resistances of arms, trunk and legs as measured by eight-polar BIA (InBody 3.0, Biospace, Seoul, Korea). The resistance index at a frequency of x kHz (RI(x)) was calculated as height (2)/R(x). RESULTS: ECW : TBW was similar in women with class III (46+/-3%, mean+/-s.d.) and class I-II obesity (45+/-3%) but higher than in nonobese women (39+/-3%, P<0.05). In a random subsample of 37 subjects, RI(500) explained 82% of TBW variance (P<0.0001) and cross-validation of the obtained algorithm in the remaining 38 subjects gave a percent root mean square error (RMSE%) of 5% and a pure error (PE) of 2.1 l. In the same subjects, RI(5) explained 87% of ECW variance (P<0.0001) and cross-validation of the obtained algorithm gave a RMSE% of 8% and a PE of 1.4 l. The contribution of weight and BMI to the prediction of TBW and ECW was nil or negligible on practical grounds. CONCLUSIONS: ECW : TBW is similar in women with class I-II and class III obesity up to BMI values of 48.2 kg/m(2). Eight-polar BIA offers accurate estimates of TBW and ECW in women with a wide range of BMI (19.1-48.2 kg/m(2)) without the need of population-specific formulae.