Dual X-ray absorptiometry model for characterizing water in the human forearm using multiple frequency bioimpedance analysis

The purpose of this study was to develop a method for measuring intracellular (ICW) and extracellular water (ECW) in the human forearm using multiple frequency bioimpedance analysis (MFBIA). The approach was (i) to measure whole-body and forearm fat-free mass using dual X-ray absorptiometry (DXA); (ii) to use these measurements to estimate the fat-free mass (FFM) resistivity in both the forearm and in the whole body; and (iii) to use the ratio of these FFM resistivities to estimate the resistivity in the ICW and ECW compartments of the forearm. To first demonstrate the accuracy of the DXA software in differentiating lean body mass from fat and bone within a volume of tissue, ex-vivo bovine muscle tissue samples (n = 3) were used to approximate the physical properties of the human forearm. It was found that although the human whole-body software overestimates FFM, it was slightly underestimated by the small animal software. Using this technique, DXA measures of FFM were obtained from human volunteers (n = 11; age = 20 +/- 5 years; height = 170 +/- 12 cm; mass = 64 +/- 16 kg). These measures were used in conjunction with MFBIA measures of impedance of the whole body and of the forearm to determine the resistivities of the ICW and ECW compartments of the forearm, namely 375.8 +/- 25.2 ohms cm and 55.6 +/- 3.7 ohms cm, respectively. These were used in MFBIA equations to calculate the ICW, ECW, and total arm water (TAW) volumes of the human forearm. The calculated TAW and the ECW (+/- SD) volume fraction (667.29 +/- 200.15 mL and 0.169 +/- 0.039 mL, respectively) were in agreement with literature values. MFBIA results were compared with those obtained using nuclear magnetic resonance relaxometry (NMRR). MFBIA was performed on 15 subjects before and after an intense maximal handgrip exercise to estimate changes in water volume in muscle. Following exercise, the total and intracellular water of the forearm increased on average by 8% +/- 3% and 10% +/- 4% (mean +/- SD), respectively. In 5 healthy volunteers, MFBIA and NMRR were performed before and after a similar exercise of the forearm muscle. The changes with exercise of intracellular and total arm water volumes as measured by MFBIA were estimated. The percent increases in total water were found to be 9.4% +/- 4.2% and 9.4% +/- 2.6% and in intracellular water were found to be 10.6% +/- 4.6% and 12.0% +/- 2.8% (mean +/- SD) for NMRR and MFBIA, respectively. The results show that the exercise-induced changes in ICW and TAW determined with the MFBIA model are consistent with those observed with NMRR and radiotracer literature.     

Dual-energy X-ray absorptiometry lean soft tissue hydration: independent contributions of intra- and extracellular water

Dual-energy X-ray absorptiometry (DEXA) provides a measure of lean soft tissue (LST). LST hydration, often assumed to be constant, is relevant to several aspects of DEXA body composition estimates. The aims of this study were to develop a theoretical model of LST total body water (TBW) content and to examine hydration effects with empirically derived model coefficients and then to experimentally test the model's prediction that, in healthy adults, LST hydration is not constant but varies as a function of extra- and intracellular water distribution (E/I). The initial phase involved TBW/LST model development and application with empirically derived model coefficients. Model predictions were then tested in a cross-sectional study of 215 healthy adults. LST was measured by DEXA, extracellular water (ECW) by NaBr dilution, intracellular water (ICW) by whole body (40)K counting, and TBW by (2)H(2)O dilution. TBW estimates, calculated as ECW + ICW, were highly correlated with (r = 0.97, SEE = 2.1 kg, P < 0.001) and showed no significant bias compared with TBW measured by (2)H(2)O. Model-predicted TBW/LST was almost identical to experimentally derived values (means +/- SD) in the total group (0.767 vs. 0.764 +/- 0.028). LST hydration was significantly correlated with E/I (total group, r = 0.30, SEE = 0.027, P < 0.001). Although E/I increased with age (men, r = 0.48; women, r = 0.37; both P < 0.001), the association between TBW/LST and age was nonsignificant. Hydration of the DEXA-derived LST compartment is thus not constant but varies predictably with ECW and ICW distribution. This observation has implications for the accuracy of body fat measurements by DEXA and the use of TBW as a means of checking DEXA system calibration.     

Effect of subclinical hypothyroidism on body fluid compartments.

OBJECTIVE: The present study was aimed to assess the effects of subclinical hypothyroidism on body composition (BC). SUBJECTS: Thirty-one women (age: 37 +/- 9.9 years) with a wide range of body mass index (BMI) were studied. Subclinical hypothyroidism was defined by a basal TSH > or = 4 mU/L and/or TRH stimulated peak > or = 30 mU/L. MEASUREMENTS: For each subject, weight, height, BMI, multifrequency bioelectrical impedance spectroscopy (BIS) and D2O and NaBr dilution tests were performed to assessed total body water (TBW) and extracellular water (ECW). Thyroid function (basal and TRH stimulated TSH, free T3, and free T4) were determined from fasting blood samples for all subjects. Total body dual energy X-ray absorptiometry (DXA) were used to measure fat mass (FM) and lean mass (Lean). RESULTS: The results of BIS were compared with the TBW and ECW estimated by the dilution techniques on the same individuals. The correlation was R2 = 0.65 for impedance at 5 kHz and ECW by NaBr and R2 = 0.72 for impedance at 100 kHz and TBW by D2O. Intracellular water (ICW) was calculated as differences between TBW and ECW measured by dilution methods. Percent of ECW and ICW were related to BMI (ANOVA, p < 0.001). No difference in TBW, body water distribution and body composition related to thyroid function was demonstrated. CONCLUSIONS: In our patients affected with subclinical hypothyroidism, with or without obesity, only obesity appeared related to TBW, ECW and ICW; the subclinical hypothyroidism, on the contrary, had no effect on compartments of body fluids. Bioimpedance is a valid tool to assess body fluid distribution in subclinical hypothyroidism.     

Extracellular water: greater expansion with age in African Americans.

Aging is associated with the onset of chronic diseases that lead to pathological expansion of the extracellular water (ECW) compartment. Healthy aging, in the absence of disease, is also reportedly accompanied by a relative expansion of the ECW compartment, although the studies on which this observation is based are few in number, applied different ECW measurement methods, included small ethnically homogeneous subject samples, and failed to adjust ECW for non-age-related influencing factors. The aim of the current study was to examine, in a large (n = 1,538) ethnically diverse [African American (AA), Asian, Caucasian, Hispanic] subject group the cross-sectional relationships between ECW and age after controlling first for other potential factors that may influence fluid distribution. ECW and intracellular water (ICW) were derived from measured total body water (isotope dilution) and potassium (40K whole body counting). The cross-sectional relationships between ECW, ICW, and ECW/ICW (E/I), and age were developed using multiple regression modelling methods. Body weight, weight squared, height, age, sex, race, and interactions were all significant ECW predictors. The slope of the observed race x age interaction was significantly greater in AA (beta = 0.0005, P = 0.005) than in the three other race groups. Race, sex, and age differences in fluid distribution persisted after adjusting for body composition in a subgroup (n = 994) with dual-energy X-ray absorptiometry lean soft tissue and fat measurements. A relative ECW expansion (i.e., E/I) was present with greater age in most sex-race groups, although the effect was not significantly larger in AA males (P > 0.05) compared with the other race groups, except Asians (P < 0.05). For females, a larger E/I-age effect was found in AA compared with the other race groups, but only the comparison against Hispanics was significant (P < 0.05). The ECW compartment and E/I are thus variably larger, according to race, in healthy older subjects independent of sex, lean soft tissue, and fat mass.     

Single- and multifrequency models for bioelectrical impedance analysis of body water compartments.

The 1994 National Institutes of Health Technology Conference on bioelectrical impedance analysis (BIA) did not support the use of BIA under conditions that alter the normal relationship between the extracellular (ECW) and intracellular water (ICW) compartments. To extend applications of BIA to these populations, we investigated the accuracy and precision of seven previously published BIA models for the measurement of change in body water compartmentalization among individuals infused with lactated Ringer solution or administered a diuretic agent. Results were compared with dilution by using deuterium oxide and bromide combined with short-term changes of body weight. BIA, with use of proximal, tetrapolar electrodes, was measured from 5 to 500 kHz, including 50 kHz. Single-frequency, 50-kHz models did not accurately predict change in total body water, but the 50-kHz parallel model did accurately measure changes in ICW. The only model that accurately predicted change in ECW, ICW, and total body water was the 0/infinity-kHz parallel (Cole-Cole) multifrequency model. Use of the Hanai correction for mixing was less accurate. We conclude that the multifrequency Cole-Cole model is superior under conditions in which body water compartmentalization is altered from the normal state.     

Relationship between changes in total-body water and fluid distribution with maximal forearm strength in elite judo athletes

Among judo athletes, strong grip strength is crucial for performing offensive and defensive maneuvers that rely predominantly on forearm maximal strength (FMS). The study aims were to evaluate changes in total-body water (TBW) and its compartments (extracellular water [ECW] and intracellular water [ICW]) and their relationship with loss of FMS in elite judo athletes. At baseline (weight stability), 27 male elite athletes were evaluated (age: 23.2 ± 2.8 years) and again evaluated 1-3 days before competition. Athletes were free to gain or lose weight based upon their specific competition needs. Using dilution techniques (deuterium and bromide), TBW and ECW were estimated, and ICW was calculated (ICW = TBW - ECW). Fat, fat-free mass, and appendicular lean soft tissue (LST) were assessed by dual-energy x-ray absorptiometry. Handgrip was used to assess FMS. Using a reduction of 2% as a representative outcome for decreased FMS, 10 athletes were identified as having lost FMS, whereas 17 changed <2% or gained. Comparison of means and logistic regression analysis were performed. Results from baseline to before competition indicated that those who lost ≥2% of FMS significantly decreased TBW and ICW by -2.7 ± 3.0 and -4.4 ± 4.2%, respectively. The groups differed in ICW changes (-4.4 ± 4.2 vs. 1.9 ± 6.1%), respectively, for those who lost FMS by ≥2%. The ICW changes, but not in TBW or ECW, significantly predicted the risk of losing FMS (β = 0.206; p = 0.027), even adjusting for weight and arm LST changes. These findings indicated that reductions in ICW increased the risk of losing grip strength in elite judo athletes.     

Measurement of nutritional status in simulated microgravity by bioelectrical impedance spectroscopy.

The potential of bioelectrical impedance spectroscopy (BIS) for assessing nutritional status in spaceflight was tested in two head-down-tilt bed-rest studies. BIS-predicted extracellular water (ECW), intracellular water (ICW), and total body water (TBW) measured using knee-elbow electrode placement were compared with deuterium and bromide dilution (DIL) volumes in healthy, 19- to 45-yr-old subjects. BIS was accurate during 44 h of head-down tilt with mean differences (BIS - DIL) of 0-0.1 kg for ECW, 0.3-0.5 for ICW, and 0.4-0.6 kg for TBW (n = 28). At 44 h, BIS followed the within-individual change in body water compartments with a relative prediction error (standard error of the estimate/baseline volume) of 2.0-3.6% of water space. In the second study, BIS did not detect an acute decrease (-1.41 +/- 0.91 kg) in ICW secondary to 48 h of a protein-free, 800 kcal/day diet (n = 18). BIS's insensitivity to ICW losses may be because they were predominantly (65%) localized to the trunk and/or because there was a general failure of BIS to measure ICW independently of ECW and TBW. BIS may have potential for measuring nutritional status during spaceflight, but its limitations in precision and insensitivity to acute ICW changes warrant further validation studies.     

Postpartum changes in body composition

Parity is associated with weight retention and has long-lasting and detrimental effects on the health of women. Previous studies have shown that increasing parity was independently associated with an increased prevalence of metabolic syndrome. Postpartum weight is made up of several components including uterine and mammary tissues, body water (intracellular (ICW) and extracellular water (ECW)), and fat. These components change in variable amounts postpartum, thereby distinctly affecting the interpretation of individual weight retention; however, it is unclear which components contribute to weight retention. The aims of this longitudinal study were to evaluate changes in body composition during the postpartum period and to investigate their effects on weight retention. This prospective study examined 41 healthy, pregnant women who gave birth at Korea University Guro Hospital. We measured body composition at 2 days, 2 weeks, and 6 weeks postpartum using bioelectrical impedance analysis. Weight decreased during this postpartum period (P < 0.001); the postpartum weight retention from prepregnancy to 6 weeks postpartum was 4.43 ± 4.0 kg. Among various body composition components, ECW, ICW, total body water, and fat-free mass (FFM) decreased postpartum. However, fat mass (FM) and visceral fat area, the components that experienced the greatest changes, increased postpartum. Our results demonstrate that the postpartum period is associated with a preferential accumulation of adipose tissue in the visceral compartment, even though overall body weight is decreased. Further studies are needed to evaluate the changes in body composition over longer time periods and their long-term effects on health.     

Evaluation of bioimpedance spectroscopy for measurements of body water distribution in healthy women before, during, and after pregnancy.

Bioimpedance spectroscopy (BIS) is a technique of interest in the study of human pregnancy because it can assess extracellular (ECW), intracellular (ICW), and total body water (TBW) as ECW plus ICW. The technique requires appropriate resistivity coefficients and has not been sufficiently evaluated during the reproductive cycle. Therefore, in a methodological study, we estimated ECW, ICW, and TBW, by means of BIS, and compared the results with the corresponding estimates obtained by using reference methods. Furthermore, results obtained by means of population-specific resistivity coefficients were compared with results obtained by means of general resistivity coefficients. These comparisons were made before pregnancy, in gestational weeks 14 and 32, as well as 2 wk postpartum in 21 healthy women. The reference methods were isotope and bromide dilution. Average ICW, ECW, and TBW, estimated by means of BIS, were in agreement with reference data before pregnancy, in gestational week 14, and postpartum. The corresponding comparison in gestational week 32 showed good agreement for ICW, whereas estimates by means of BIS were significantly (P < 0.001) lower than the corresponding reference values for ECW and TBW. Thus the BIS technique, which was based on a model developed for the nonpregnant body, estimated increases in ICW accurately, whereas increases in ECW and TBW tended to be underestimated. Estimates obtained by using population-specific and general resistivity coefficients were very similar. In conclusion, the results indicated that BIS is potentially useful for studies during pregnancy but that further work is needed before it can be generally applied in such studies.     

Use of bioelectrical impedance spectroscopy to provide a measure of body composition in sows

The ability to accurately estimate fat mass and fat-free mass (FFM) has the potential to improve the way in which sow body condition can be managed in a breeding herd. Bioelectrical impedance spectroscopy (BIS) has been evaluated as a practical technique for assessment of body composition in several livestock species, but similar work is lacking in sows. Bioelectrical impedance uses population-specific algorithms that require values for the apparent resistivities of body fluids and body proportion factors. This study comprised three major aims: (i) to derive apparent resistivity coefficients for extracellular water (ECW) and intracellular water (ICW) required for validation of BIS predictions of total body water (TBW) in live sows against standard reference tracer dilution methods; (ii) to develop predictions of TBW to body composition prediction algorithms, namely FFM, by developing a body geometry correction factor (Kb) and (iii) to compare the BIS predictions of FFM against existing impedance predictors and published prediction equations for use in sows, based on physical measurements of back-fat depth and BW (P2-based predictors). Whole body impedance measurements and the determination of TBW by deuterium dilution and ECW by bromide dilution were performed on 40 Large White x Landrace sows. Mean apparent resistivity coefficients of body fluids were 431.1 Ω.cm for ECW and 1827.8 Ω.cm for ICW. Using these coefficients, TBW and ECW were over-estimated by 6.5 and 3.3%, respectively, compared to measured reference values, although these differences were not statistically different (P > 0.05). Mean Kb was 1.09 ± 0.14. Fat-free mass predictions were 194.9 kg, which equates to 60.9% of total sow weight, and 183.0 kg for BIS and the deuterium dilution method, respectively. Mean differences between the predicted and measured FFM values ranged from − 8.2 to 32.7%, but were not statistically different (P > 0.05). Method validation (leave-one-out procedure) revealed that mean differences between predicted and measured values were not statistically significant (P > 0.05). Of the impedance-based predictors, equivalence testing revealed that BIS displayed the lowest test bias of 11.9 kg (8.2%), although the P2-based prediction equations exhibited the lowest bias and percentage equivalence, with narrow limits of agreement. Results indicate although differences between mean predicted and measured values were not significantly different, relatively wide limits of agreement suggest BIS as an impractical option for assessing body composition in individual sows compared to the use of existing prediction equations based on BW and back fat.     

Contribution of genetic and environmental factors to variation in body compartments--a twin study in adults

This study aimed at analyzing the contribution of genetic and environmental factors on phenotypic variation of various traits of body composition. Subjects were 30 same-sexed pairs of twins including 20 monozygous (MZ) and 10 dizygous (DZ) pairs, aged 19-62 years. Zygosity was determined by DNA typing and morphological diagnosis. Body composition parameters (fat mass FM, lean body mass LBM, body cell mass BCM, extracellular mass ECM, total body water TBW, extracellular water ECW, and intracellular water ICW) were estimated by tetrapolar bioelectrical impedance analysis. Potential environmental factors influencing body composition (number of children, sporting activity and smoking behaviour) were determined by questionnaires. Heritabilities for traits of body composition were calculated by use of the twin method. Intraclass correlation is > 0.80 for the variation of LBM, BCM, ECM, TBW, ECW, and ICW in both MZ and DZ twins. Estimated heritability (h2) for FM, LBM, BCM, ECW, TBW, ECW, and ICW is 65%, 77%, 79%, 83%, 76%, 68%, and 82%, respectively. The h2 values for FM and LBM are consistent with those reported in other twin studies. For BCM, ECM, ECW and ICW, no comparative h2 estimates exist. Within-pair differences in body compartments do not change with increasing age in MZ and DZ twin pairs (p > 0.05). Stepwise multiple regression analyses indicate that zygosity, age, sex, number of children, sporting level and smoking behaviour do not significantly predict within-pair differences for weight, BMI, FM, LBM, TBW, ECW and ICW (each, p > 0.05). In contrast, sex and the number of children explain together 27% of observed within-pair differences for BCM. Zygosity is the only significant predictor of within-pair differences for ECM and height, explaining 20% (p = 0.008) and 36% of variance, respectively (p < 0.0001). Results indicate that genetic factors exert stronger influences on body composition than the considered environmental traits.     

Weight loss in postmenopausal obesity: no adverse alterations in body composition and protein metabolism

We sought to determine if decrements in the mass of fat-free body mass (FFM) and other lean tissue compartments, and related changes in protein metabolism, are appropriate for weight loss in obese older women. Subjects were 14 healthy weight-stable obese (BMI > or =30 kg/m(2)) postmenopausal women >55 yr who participated in a 16-wk, 1, 200 kcal/day nutritionally complete diet. Measures at baseline and 16 wk included FFM and appendicular lean soft tissue (LST) by dual-energy X-ray absorptiometry; body cell mass (BCM) by (40)K whole body counting; total body water (TBW) by tritium dilution; skeletal muscle (SM) by whole body MRI; and fasting whole body protein metabolism through L-[1-(13)C]leucine kinetics. Mean weight loss (+/-SD) was 9.6+/-3.0 kg (P<0.0001) or 10.7% of initial body weight. FFM decreased by 2.1+/-2.6 kg (P = 0.006), or 19.5% of weight loss, and did not differ from that reported (2.3+/-0.7 kg). Relative losses of SM, LST, TBW, and BCM were consistent with reductions in body weight and FFM. Changes in [(13)C]leucine flux, oxidation, and synthesis rates were not significant. Follow-up of 11 subjects at 23.7 +/-5.7 mo showed body weight and fat mass to be below baseline values; FFM was nonsignificantly reduced. Weight loss was accompanied by body composition and protein kinetic changes that appear appropriate for the magnitude of body mass change, thus failing to support the concern that diet-induced weight loss in obese postmenopausal women produces disproportionate LST losses.     

Human hydrometry: comparison of multifrequency bioelectrical impedance with 2H2O and bromine dilution

The traditionalmethod of assessing total body water (TBW), extracellular water (ECW),and intracellular water (ICW) has been the use of isotopes, on thebasis of the dilution principle. Although the development ofbioelectrical impedance techniques has eliminated many of themeasurement constraints associated with the dilution methods, thedegree of interchangeability between the two methods remains uncertain.We used multifrequency bioelectrical impedance spectroscopy (BIS),²H₂Odilution, and bromine dilution to assess TBW, ECW, and ICW in 469 healthy subjects (248 males, 221 females) aged 3-29 yr. We foundthat the TBW, ECW, and ICW estimates for the BIS and dilution methodswere significantly correlated(r² = 0.80-0.96, P < 0.0001, SE ofthe estimate = 2.3-2.7 liters). On the basis of population, theconstants used in the BIS analysis could be adjusted so that the meandifferences with the dilution methods would become zero. The SD valuesfor the mean differences between the dilution and BIS methods, however,remained significant for both males and females: TBW (±2.1-2.8liters), ECW (±1.4-1.6 liters), and ICW (2.0-3.1 liters).To improve the accuracy of the BIS measurement for an individual withinthe age range we have examined, further refinement of the constantsused in the BIS analysis is needed.

     

Responses of adipose tissue lipoprotein lipase to weight loss affect lipid levels and weight regain in women

This study determines whether changes in abdominal (ABD) and gluteal (GLT) adipose tissue lipoprotein lipase (LPL) activity in response to a 6-mo weight loss intervention, comprised of a hypocaloric diet and low-intensity walking, affect changes in body composition, fat distribution, lipid metabolism, and the magnitude of weight regain in 36 obese postmenopausal women. Average adipose tissue LPL activity did not change with an average 5.6-kg weight loss, but changes in LPL activity were inversely related to baseline LPL activity (ABD: r = -0.60, GLT: r = -0.48; P < 0.01). The loss of abdominal body fat and decreases in total and low-density lipoprotein cholesterol were greater in women whose adipose tissue LPL activity decreased with weight loss despite a similar loss of total body weight and fat mass. Moreover, weight regain after a 6-mo follow-up was less in women whose adipose tissue LPL activity decreased than in women whose LPL increased (ABD: 0.9 +/- 0.5 vs. 2.8 +/- 0.6 kg, P < 0.05; GLT: 0.2 +/- 0.5 vs. 2.8 +/- 0.5 kg, P < 0.01). These results suggest that a reduction in adipose tissue LPL activity with weight loss is associated with improvements in lipid metabolic risk factors with weight loss and with diminished weight regain in postmenopausal women.     

Effects of a competitive wrestling season on body composition, strength, and power in National Collegiate Athletic Association Division III college wrestlers

The purpose of this study was to investigate the effects of a competitive wrestling season on body composition, muscular strength, and muscular power in National Collegiate Athletic Association (NCAA) Division III college wrestlers. A total of 10 wrestlers were assessed throughout 2 consecutive wrestling seasons in late October, late January (midseason), and late March (postseason). Measurements included body weight, body composition (6-site skinfold), muscular strength (back squats and bench press), and muscular power (e.g., power cleans, vertical jump, seated medicine ball put). A repeated-measures analysis of variance (ANOVA) showed no significant changes in body weight, percentage of body fat, or fat-free mass (FFM) from pre- to mid- to postseason (body weight, 77.9 +/- 12.4, 75.7 +/- 11.0, and 79.9 +/- 12.8 kg; percentage of body fat, 11.6 +/- 3.9, 10.5 +/- 3.0, and 12.0 +/- 3.4; FFM, 68.5 +/- 8.7, 67.5 +/- 8.2, and 70.0 +/- 9.0 kg). A statistically significant main effect of time (p < 0.01) was observed for muscular strength, as both the back squat and bench press measures were lower at midseason (back squat, 150.8 +/- 25.2 kg; bench press, 98.3 +/- 25.4 kg) than at pre- and postseason (back squat, 157.9 +/- 25.5 and 161.4 +/- 25.6; bench press, 103.4 +/- 25.5 and 106.4 +/- 26.0). Muscular power did not change significantly throughout the wrestling season. These data indicate that Division III college wrestlers remain relatively weight stable with little change in body composition during a competitive wrestling season. While muscular power is apparently maintained, muscular strength may decline slightly. Our findings suggest that these wrestlers benefit from a training program that emphasizes in-season strength maintenance.     

Predicting body cell mass with bioimpedance by using theoretical methods: a technological review

De Lorenzo, A., A. Andreoli, J. Matthie, and P. Withers.Predicting body cell mass with bioimpedance by using theoretical methods: a technological review. J. Appl.Physiol. 82(5): 1542-1558, 1997.The body cellmass (BCM), defined as intracellular water (ICW), was estimated in 73 healthy men and women by total body potassium (TBK) and by bioimpedancespectroscopy (BIS). In 14 other subjects, extracellular water (ECW) andtotal body water (TBW) were measured by bromide dilution and deuteriumoxide dilution, respectively. For all subjects, impedance spectral datawere fit to the Cole model, and ECW and ICW volumes were predicted byusing model electrical resistance terms R_E andR_I in an equation derived from Hanai mixture theory,respectively. The BIS ECW prediction bromide dilution wasr = 0.91, standard error of theestimate (SEE) 0.90 liter. The BIS TBW prediction of deuterium spacewas r = 0.95, SEE 1.33 liters. The BISICW prediction of the dilution-determined ICW wasr = 0.87, SEE 1.69 liters. The BIS ICWprediction of the TBK-determined ICW for the 73 subjects wasr = 0.85, SEE = 2.22 liters. Theseresults add further support to the validity of the Hanai theory, theequation used, and the conclusion that ECW and ICW volume can bepredicted by an approach based solely on fundamental principles.

     

Effect of race and resistance training status on the density of fat-free mass and percent fat estimates.

The impact of race and resistance training status on the assumed density of the fat-free mass (D(FFM)) and estimates of body fatness via hydrodensitometry (%Fat(D)) vs. a four-component model (density, water, mineral; %Fat(D,W,M)) were determined in 45 men: white controls (W; n = 15), black controls (B; n = 15), and resistance-trained blacks (B-RT; n = 15). Body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by dual-energy X-ray absorptiometry were used to estimate %Fat(D,W,M). D(FFM) was not different between B and W (or 1.1 g/ml); however, D(FFM) in B-RT was significantly lower (1.091 +/- 0.012 g/ml; P < 0.05). Therefore, %Fat(D) using the Siri equation was not different from %Fat(D,W,M) in W (17.5 +/- 5.0 vs. 18.3 +/- 5.4%) or B (14.9 +/- 5.6 vs. 15.7 +/- 5.7%) but significantly overestimated %Fat(D,W,M) in B-RT (14.0 +/- 5.9 vs. 10.4 +/- 6.0%; P < 0.05). The use of a race-specific equation (assuming D(FFM) = 1.113 g/ml) did not improve the agreement between %Fat(D) and %Fat(D,W,M), resulting in a significantly greater mean (+/-SD) discrepancy for B (1.7 +/- 1.8% fat) and B-RT (6.2 +/- 4.3% fat). Thus race per se does not affect D(FFM) or estimates of %Fat(D); however, B-RT have a D(FFM) lower than 1.1 g/ml, leading to an overestimation of %Fat(D).     

Metabolically active portion of fat-free mass: a cellular body composition level modeling analysis

The proportion of fat-free mass (FFM) as body cell mass (BCM) is highly related to whole body resting energy expenditure. However, the magnitude of BCM/FFM may have been underestimated in previous studies. This is because Moore's equation [BCM (kg) = 0.00833 x total body potassium (in mmol)], which was used to predict BCM, underestimates BCM by approximately 11%. The aims of the present study were to develop a theoretical BCM/FFM model at the cellular level and to explore the influences of sex, age, and adiposity on the BCM/FFM. Subjects were 112 adults who had the following measurements: total body water by (2)H(2)O or (3)H(2)O dilution; extracellular water by NaBr dilution; total body nitrogen by in vivo neutron activation analysis; and bone mineral by dual-energy X-ray absorptiometry. FFM was calculated using a multicomponent model and BCM as the difference between FFM and the sum of extracellular fluid and solids. The developed theoretical model revealed that the proportion of BCM to FFM is mainly determined by water distribution (i.e., E/I, the ratio of extracellular to intracellular water). A significant correlation (r = 0.90, P < 0.001) was present between measured and model-predicted BCM/FFM for all subjects pooled. Measured BCM/FFM [mean (SD)] was 0.584 +/- 0.041 and 0.529 +/- 0.041 for adult men and women (P < 0.001), respectively. A multiple linear regression model showed that there are independent significant associations of sex, age, and fat mass with BCM/FFM.     

Changes in tissue water content measured with multiple-frequency bioimpedance and metabolism measured with 31P-MRS during progressive forearm exercise.

Multiple-frequency bioimpedance analysis (MFBIA) has been used to determine the cellular water composition in the human body. It is noninvasive and has demonstrated good correlations with other invasive measures of tissue water. However, the ability of this method to study transient changes in tissue water in specific muscle groups has not been explored. In this study, MFBIA was used to assess changes in forearm intracellular water (ICW), extracellular water (ECW), and total water (TW) in seven healthy volunteers during and after a progressive wrist flexion exercise protocol. In an identical trial, (31)P magnetic resonance spectroscopy ((31)P-MRS) was used to assess changes in intracellular pH and phosphocreatine (PCr). At the completion of exercise, forearm ICW increased 12.6% (SD 0.07, P = 0.003), TW increased 10.1% (SD 0.06, P = 0.005), and no significant changes were recorded for ECW. A significant correlation was found between the changes in intracellular pH and changes in ICW during exercise (r = -0.84, P = 0.018). With the use of regression analysis, average changes in P(i), PCr, and pH were found to predict changes in ICW (R(2) = 0.98, P = 0.005). In conclusion, MFBIA was sensitive enough to measure transient changes in the exercising forearm muscle. The changes seen were consistent with the hypothesis that intracellular acidification and PCr hydrolysis are important mediators of cellular osmolality and therefore may be responsible for the increased volume of water in the intracellular space that is often recorded after short-term high-intensity exercise.     

Contributing factors and variability of energy expenditure in non-obese, obese, and post-obese adolescents

Energy expenditure (EE) is a major determinant of energy balance and body composition. The objectives of this paper were to review the contributing factors of the main components of daily EE (DEE) and the inter-individual variability in these components in non-obese (NOb), obese (Ob), and post-obese (POb) adolescents. Body composition especially fat-free mass (FFM), is the major determinant of the basal metabolic rate which contributes 50-70% of DEE, whereas fat mass (FM) is a significant factor only in obese subjects. Physical activity is the second main variation factor of DEE, whereas growth, the thermic effect of food, and thermoregulation are generally of marginal importance. The energy costs and EE associated with various sedentary and physical activities were assessed in NOb, Ob and POb subjects both in standardised and in free-living conditions. The interindividual variability of DEE is high, even after adjustment for body composition, mainly because of great differences in time devoted to the various physical activities. DEE and EE associated with sleep and sedentary activities are significantly higher in Ob than in NOb, but not after adjustment for FFM. On the contrary, EE associated with physical activities is not significantly different between Ob and NOb adolescents, but 61% lower in Ob subjects after adjustment for body composition. Multidisciplinary weight-reduction programmes including moderate energy restriction and physical training result in great FM loss, maintenance of FFM, improvement of physical capacities, but reductions in organ and tissue metabolic rate and in EE associated with the various sedentary and physical activities, which may favour body weight regain in the less active POb subjects.