Body composition following hemodialysis: studies using dual-energy X-ray absorptiometry and bioelectrical impedance analysis

Effect of exercise-induced body fluid redistribution on body composition in males using dual energy X-ray absorptiometry

We studied the effect of exercise-induced body fluid redistribution on dual-energy x-ray absorptiometry (DXA) body composition scores. Thirty males completed 30-min of upper-body exercise (UBE), lower-body exercise, and seated non-exercise control (NEC). ANOVA determined interactions between experimental conditions and measurements on body composition variables. For UBE, mean pre to post differences were found on tissue fat (M = 0.35 ± 0.12%; CI95%diff = 0.10 to 0.59%; p = 0.007), region fat (M = 0.32 ± 0.11%; CI95%diff = 0.09 to 0.55%; p = 0.008), lean mass (M = 0.27 ± 0.01 kg; CI95%diff = 0.18 to 0.37 kg; p ≤ 0.0001), and total mass (M = 0.27 ± 0.05 kg; CI95%diff = 0.17 to 0.36 kg; p ≤ 0.0001). Mean tissue pre to post differences were found for the total body in the NEC (M = 0.10 ± 0.04 kg; CI95%diff = 0.03 to 0.18 kg; p = 0.008), UBE (M = 0.19 ± 0.03 kg; CI95%diff = 0.14 to 0.24 kg; p ≤ 0.0001), and LBE (M = 0.31 ± 0.04 kg; CI95%diff = 0.24 to 0.39 kg; p ≤ 0.0001) conditions. High absolute reliability was found within experimental conditions. These findings have practical implications for technicians, since acute exercise elicited small changes in body composition scores using DXA.

Association between low handgrip strength and obesity with mortality in peritoneal dialysis patients

The association between sarcopenia and obesity in peritoneal dialysis (PD) patients is more complex than that of the general population. The aim of this study was, therefore, to evaluate the association of patient survival with sarcopenia or sarcopenic components and obesity in groups of patients with PD. We retrospectively analyzed a dataset from 199 prevalent PD patients. Measurements including handgrip strength (HGS), appendicular lean mass index, and baseline characteristics, were obtained during the period of study. Patients were divided into four groups according to their HGS and obesity: NH-NO (normal HGS and non-obesity, n = 60), NH-O (normal HGS and obesity, n = 31), LH-NO (low HGS and non-obesity, n = 71), and LH-O (low HGS and obesity, n = 37). The median follow-up interval was 17 months. The Kaplan-Meier curve analysis showed that the LH-O group had the poorest patient survival outcome among the four groups (P < 0.001). The NH-NO group had a better patient survival outcome compared with the LH-NO group. Univariate and multivariate Cox regression analyses showed that the LH-O group had the highest mortality rate compared with the other groups. The NH-NO group had lower mortality compared with the LH-NO group. The present study demonstrated that obesity with low HGS was associated with the greatest mortality rate in groups defined by HGS and obesity.

Utility of Trabecular Bone Score (TBS) in Bone Quality and Fracture Risk Assessment in Patients on Maintenance Dialysis

Maintenance dialysis is associated with almost universal changes in bone metabolism collectively known as chronic kidney disease—mineral and bone disorder (CKD-MBD). These are accompanied in various proportions by bone loss and altered bone quality that led to an increased risk of fracture. Osteoporosis, age-related or postmenopausal, a condition that often coexists with CKD, is also a leading cause of fracture. Dual-energy X-ray densitometry (DXA) is the main tool for assessing the bone quantity and bone loss and the associated fracture risk. It has been validated in both CKD-MBD and osteoporosis. Trabecular bone score (TBS) is a DXA-derived algorithm for the evaluation of bone microarchitecture, and its clinical value has been repeatedly demonstrated in large cohorts of osteoporotic patients. However, its utility in patients on maintenance dialysis has not been conclusively shown. Published studies showed a lower TBS score and implicitly an altered bone microarchitecture in patients on maintenance dialysis, even after adjusting for various variables. Moreover, FRAX-based fracture risk is higher after adjusting for TBS, showing promise on an algorithm better estimating the clinical fracture risk in dialysis patients. However, TBS has not been demonstrated to independently predict clinical fractures in prospective studies on dialysis patients. Also, aortic calcifications and altered fluid balance could significantly affect TBS score and could hamper the widespread clinical use in patients on maintenance dialysis. In this mini-review, we focus on the benefits and pitfalls of TBS in the management of CKD-MBD and fracture risk assessment in patients on maintenance dialysis.

Association Between Phase Angle and Sarcopenia in Patients Undergoing Peritoneal Dialysis

Introduction: There is limited data on the association between phase angle (PhA) and sarcopenia using both muscle strength and muscle mass in patients undergoing peritoneal dialysis (PD). We aimed to evaluate the association between PhA and sarcopenia in patients undergoing PD.

Methods: We enrolled prevalent patients undergoing PD (n = 200). The patients were divided into tertiles based on their PhA level: low (n = 66; 1.9–4°), middle (n = 68; 4.1–4.9°), and high tertiles (n = 66; 5–8°). PhA was measured by a bioimpedance analysis. Handgrip strength (HGS) was measured in all the patients. Body compositions were measured by dual energy x-ray absorptiometry (DXA).

Results: Handgrip strength (HGS) and/or lean mass indices showed poorer trends in the low tertile than in the other tertiles. PhA was positively associated with HGS and/or muscle mass index. Multivariate analyses showed that the patients in the low tertile had an odds ratio of 9.8 (p = 0.001) and 52.79 (p < 0.001) for developing sarcopenia compared with those in the middle and high tertiles, respectively. Subgroup analyses using these variables yielded results similar to those from the total cohort.

Conclusion: This study demonstrated that PhA is independently associated with muscle mass, strength, and sarcopenia in patients undergoing PD. This result suggests that PhA can be used as a valuable and simple predictor for identifying patients undergoing PD who are at risk of sarcopenia.

Comparison of lean mass indices as predictors of mortality in incident peritoneal dialysis patients

Background

Few studies have considered optimal adjusted lean mass indices for prediction of clinical outcomes in peritoneal dialysis (PD) patients. We aimed to evaluate clinical variables using various adjusted indices in PD patients.

Methods

Total 528 incident PD patients were included. Lean mass was measured using dual energy X-ray absorptiometry. Appendicular lean mass (ALM) was calculated using the sum for both upper and lower extremities. Each ALM index was calculated using ALM per body weight (ALM/BW), height squared (ALM/Ht²), or body mass index (ALM/BMI). Limb/trunk lean mass (LTLM) ratio was defined as the sum for both upper and lower extremities divided by trunk lean mass.

Results

A total of 528 patients were analyzed men: 286, women: 242. In area under the receiver operating characteristic curve analyses, LTLM alone was associated with 1 year mortality. In the LTLM ratio, the cut-off value for 1-year mortality was ≤ 0.829 in men and ≤ 0.717 in women, respectively. In both sexes, LTLM ratio alone showed statistical significance in all-cause mortality in both univariate and multivariate Cox-regression analyses. Compared with other indices, the LTLM ratio was independent of edema and fat in both sexes. Edema- and C-reactive protein-adjusted correlation analysis showed that LTLM ratio alone was associated with serum albumin in men. Although statistical significance was not obtained for women, the correlation coefficient was highest for the LTLM ratio compared with other indices.

Conclusion

Among various indices using lean mass, LTLM ratio was independent of volume status and fat mass and was associated with mortality in incident PD patients.

Modifiable Physical Factors Associated With Physical Functioning for Patients Receiving Dialysis: A Systematic Review

Background: Patients receiving dialysis have reduced physical function, which is associated with unfavorable clinical outcomes and decreased quality of life. The authors aimed to identify and explore modifiable physical factors associated with physical function for patients receiving dialysis. Methods: Searches were performed in MEDLINE, Embase, Ovid Emcare, and The Cochrane Library in October 2018. Etiological studies involving dialysis populations that report association or predictive statistics between a modifiable physical factor and physical function were eligible for inclusion. Predictor variables were (1) modifiable via exercise and (2) considered an impairment in the International Classification of Functioning, Disability and Health. Results: Of 5384 titles screened, 23 studies were included. Thirteen studies focused on physical activity levels and muscle strength and the relationship with physical function while 2 studies investigated sedentary behavior. Twenty-one studies focused on hemodialysis populations. Studies related to physical activity levels displayed a moderately strong relationship with physical function, whereas muscle strength displayed a predominantly weak to moderate relationship. Conclusions: Physical activity levels, sedentary behavior levels, and muscle strength are related to physical function status for patients receiving dialysis. There is a need for robust longitudinal data to confirm the results of this investigation and for more focus on populations receiving peritoneal dialysis.

Effects of volume status on body composition in incident peritoneal dialysis patients

BACKGROUND

Inadequate fluid removal or high water intake leads to overhydration, which results in malnutrition. The aim of the present study was to evaluate the effects of volume status on body composition in incident peritoneal dialysis (PD) patients.

METHODS

All incident PD patients who survived ≥1 year after PD initiation were considered eligible. A total of 366 incident PD patients were finally included and divided into three tertiles according to the time-averaged-edema index (TA-EI). The body composition parameters measured using bioimpedance analysis included the EI, fat mass index (FMI, kg/m²), and appendicular muscle mass index (AMMI, kg/m²). dFMI and dAMMI were defined as delta values for each variable. The cutoff value for sarcopenia (SP) was defined as previously reported. Patients with AMMI below the cutoff values were defined as having SP.

RESULTS

The number of participants in the low, middle, and high tertiles was 126, 100, and 140, respectively. A high volume status was associated with high solute clearance, albumin loss, and glucose absorption through the peritoneal membrane, which led to high dialysate glucose. In addition, volume status was inversely associated with increases in AMMI, but was not associated with changes in FMI. SP as a categorical variable was positively associated with a high volume status. On subgroup analyses, TA-EI had the greatest negative correlation coefficients for dAMMI.

CONCLUSION

Overhydration in PD patients was associated with decrease in muscle mass indices and the development of SP.

Chronic Kidney Disease and the Adiposity Paradox: Valid or Confounded?

OBJECTIVE

Obesity, defined by body mass index (BMI), is associated with lower mortality risk in patients with chronic kidney disease (CKD). BMI and % body fat (%BF) are confounded by muscle mass, while DXA derived fat mass index (FMI) overcomes this limitation. We compared the associations between obesity and mortality in persons with CKD using multiple estimates of adiposity, and determined whether muscle mass, inflammation and weight loss modify these associations.

METHODS

Obesity was defined using BMI and DXA-derived FMI and %BF cut-offs in 2,852 NHANES participants with CKD from 1999-2006 and linked to the National Death Index with follow up through 2011. Cox proportional hazards models assessed associations between mortality and measures of obesity.

RESULTS

Obesity based on FMI and continuous variables, FMI, BMI and %BF were associated with lower mortality. The protective association of obesity was less pronounced among participants with higher muscle mass and was no longer significant after adjustment for prior weight loss. Inflammation did not modify these associations.

CONCLUSIONS

We observed lower mortality associated with higher fat mass, particularly among persons with lower muscle mass. The prevalence of >10% weight loss was half as common among obese compared to non-obese participants and confounded these associations.

Effect of Chemotherapy on Dual-Energy X-ray Absorptiometry (DXA) Body Composition Precision Error in Head and Neck Cancer Patients

BACKGROUND

Precision error in dual-energy X-ray absorptiometry (DXA) is defined as difference in results due to instrumental and technical factors given no biologic change. The aim of this study is to compare precision error in DXA body composition scans in head and neck cancer patients before and 2 months after chemotherapy.

METHODOLOGY

A total of 34 male head and neck cancer patients with normal body mass index (BMI) were prospectively enrolled and all patients received 2 consecutive DXA scans both before and after 2 months of chemotherapy for a total of 4 scans. The precision error of 3 DXA body composition values (lean mass, fat mass, and bone mineral content) was calculated for total body and 5 body regions (arms, legs, trunk, android, and gynoid). Precision errors before and after treatment were compared using generalized estimating equation model.

RESULTS

There was no significant change in precision error for the DXA total body composition values following chemotherapy; lean mass (0.33%-0.40%, p = 0.179), total fat mass (1.39%-1.70%, p = 0.259) and total bone mineral content (0.42%-0.56%, p = 0.243). However, there were significant changes in regional precision error; trunk lean mass (1.19%-1.77%, p = 0.014) and android fat mass (2.17%-3.72%, p = 0.046).

CONCLUSIONS

For head and neck cancer patients, precision error of DXA total body composition values did not change significantly following chemotherapy; however, there were significant changes in fat mass in the android and lean mass in the trunk. Caution should be exercised when interpreting longitudinal DXA body composition data in those body parts.

Chronic hemodialysis is associated with lower trabecular bone score, independent of bone mineral density: a case-control study

We measured trabecular bone score (TBS) in 98 patients on permanent hemodialysis (HD) and 98 subjects with similar bone mineral density and normal kidney function. TBS was significantly lower in HD patients, indicating deteriorated bone microarchitecture, independent of bone mass. This might partially explain the increased fracture risk in HD.

PURPOSE

In the general population, trabecular bone score (TBS) was shown to predict fracture independent of bone mineral density (BMD). In end-stage renal disease patients on hemodialysis (HD), the value of TBS is beyond that of BMD in currently unclear. Our aim was to assess lumbar spine (LS) TBS in HD patients compared with subjects with normal kidney function matched for age, sex, and LS BMD.

METHODS

We assessed TBS and LS and femoral neck (FN) BMD in 98 patient on permanent HD (42.8% males; mean age 57.5 ± 11.3 years; dialysis vintage 5.5 ± 3.8 years) and 98 control subjects (glomerular filtration rate > 60 mL/min) using DXA. We simultaneously controlled for sex, age (± 3 years), and LS BMD (± 0.03 g/cm²).

RESULTS

HD patients had significantly lower LS TBS (0.07 [95% CI 0.03-0.1]; p = 0.0004), TBS T-score (0.83 SD [95% CI 0.42-1.24]; p = 0.0001)) and TBS Z-score (0.81 SD [95% CI 0.41-1.20]; p = 0.0001) than matched controls. TBS significantly correlated with LS BMD in both HD patients (r = 0.382; p = 0.001) and controls (r = 0.36; p = 0.002). The two regression lines had similar slopes (0.3 vs. 0.28; p = 0.84) with different intercepts (0.88 vs. 0.98). TBS adjustment significantly increased the 10-year fracture risk from 3.7 to 5.3 for major osteoporotic fracture and from 0.9 to 1.5 for hip fracture.

CONCLUSIONS

HD patients have lower TBS than controls matched for LS BMD, indicating altered bone microarchitecture. Also, the magnitude of TBS reduction in HD patients is constant at any LS BMD. Adjustment for TBS partially corrects the absolute 10-year fracture risk.

Comparison of Muscle Mass Indices Using Computed Tomography or Dual X-Ray Absorptiometry for Predicting Physical Performance in Hemodialysis Patients

BACKGROUND/AIMS

Our study aims to evaluate the association between thigh muscle cross-sectional area (TMA) using computed tomography (CT), or appendicular skeletal muscle mass (ASM) using dual energy X-ray absorptiometry (DEXA), and physical performance levels in hemodialysis (HD) patients.

METHODS

Patients were included if they were on HD for ≥6 months (n = 84). ASM and TMA were adjusted to body weight (BW, kg) or height2 (Ht2, m2). Each participant performed a short physical performance battery test (SPPB), a sit-to-stand for 30 second test (STS30), a 6-minute walk test (6-MWT), a timed up and go test (TUG), and hand grip strength (HGS) test.

RESULTS

Correlation coefficients for SPPB, GS, 5STS, STS30, 6-MWT, and TUG were highest in TMA/BW. Results from partial correlation or linear regression analyses displayed similar trends to those derived from Pearson's correlation analyses. An increase in TMA/BW or TMA/Ht2 was associated with a decreased odds ratio of low SPPB, GS, or HGS in multivariate analyses. Indices using DEXA were associated with a decreased odds ratio of a low HGS only in multivariate analysis.

CONCLUSION

TMA indices using CT may be more valuable in predicting physical performance or strength in HD patients.

Low appendicular muscle mass is associated with mortality in peritoneal dialysis patients: a single-center cohort study

BACKGROUND/OBJECTIVES

There are few studies of the association between low appendicular muscle mass (LAM) and clinical outcomes in peritoneal dialysis (PD) patients. We aimed to determine the clinical association between LAM and clinical outcomes in PD patients.

SUBJECT/METHODS

We reviewed all PD patients who underwent PD between January 2001 and April 2014. Each patient's appendicular lean mass was estimated using dual-energy X-ray absorptiometry. The appendicular muscle mass index (AMI) was calculated using total appendicular lean mass (kg) over body mass index (kg/m²). The cut-off AMI value for LAM was <0.789 for men and <0.512 for women.

RESULTS

The number of patients in the Non-LAM and LAM groups was 328 and 303, respectively. The median follow-up durations in the Non-LAM and LAM groups were 47 and 49 months, respectively. The numbers of deaths in the Non-LAM and LAM groups were 96 (29.3%) and 160 (52.8%), respectively. In a comparison with the Non-LAM group, the hazard ratio in the LAM group was 1.74 (95% confidence interval (CI), 1.35-2.24) in univariate and 1.71 (95% CI, 1.28-2.26) in multivariate Cox regression analysis. In addition, the hazard ratio for a 0.1 increase in baseline AMI was 0.89 (95% CI, 0.84-0.95) in univariate analysis and 0.84 (95% CI, 0.76-0.91) in multivariate analysis. Analyses using the 1-year AMI showed trends similar to those for the initial AMI.

CONCLUSIONS

Our study showed the association of LAM with mortality in the incident PD patients.

Bioimpedance prediction of fat-free mass from dual-energy X-ray absorptiometry in a multi-ethnic group of 2-year-old children

BACKGROUND/OBJECTIVES

Bioimpedance analysis (BIA) is a simple, convenient and widely used tool for the measurement of body composition in population surveys and surveillance. Prediction equations based on BIA applicable to preschool children are available but are based on total body water estimation and have not been developed across multiple ethnic groups. Our aim was to develop a BIA-based equation in a multi-ethnic sample of 2-year old using fat-free mass (FFM) from dual-energy X-ray absorptiometry (DXA) as criterion measure.

SUBJECTS/METHODS

Single-frequency hand-to-foot BIA (model BIM4, Impedimed) and whole-body DXA measurements were carried out in 77 (35 boys, 42 girls; 27 European, 20 Polynesian, 30 Asian and other) healthy preschool children (age range 22-38 months). Body mass index s.d. scores were 0.41 ± 1.23 for boys and 0.61 ± 1.09 for girls. The performance of published equations applicable to this age group was assessed. The predicted residual sum of squares method was used to develop and cross-validate a multiple regression equation relating FFM to BIA measures.

RESULTS

Published equations performed poorly for estimating FFM in this group of children. The prediction equation developed in all 77 children was: FFM (kg)=0.367 height(cm)(2)/resistance+0.188 weight (kg)+0.077 height (cm)+0.273 sex (male=1, female=0)-2.490, R(2)=0.89, standard error of estimate=0.50 kg. Ethnicity and age did not add significantly to the model.

CONCLUSIONS

We have developed an equation that may have application for prediction of FFM in 2-3-year-old children, which does not require determination of hydration factors. Further work should be carried out using DXA scanning to extend the applicable age range.

The influence of exogenous fat and water on lumbar spine bone mineral density in healthy volunteers

PURPOSE

Changes in human body composition can affect the accuracy of spine bone mineral density (BMD) measurements. The purpose of this study was to evaluate whether fat and water in the soft tissue of the abdomen influence lumbar spine BMD measurements obtained using dual energy X-ray absorptiometry (DXA).

MATERIALS AND METHODS

Duplicate BMD measurements were carried out on healthy volunteers (10 men and 10 women) and the Hologic anthropomorphic spine phantom had on the same day before and after placement of following 3 materials in the abdominal area: lard 900 g, 1.5 cm thick; oil 1.4 liters in a vinyl bag; and water 1.2 liters in a vinyl bag.

RESULTS

In the case of human participants, following the placement of exogenous water to mimic extracellular fluid (ECF), there was a significant decrease in lumbar spine BMD (-0.012 g/cm², p=0.006), whereas the placement of exogenous lard and oil to mimic abdominal fat produced a slight increase in lumbar spine BMD (0.006 g/cm², p=0.301; 0.008 g/cm², p=0.250, respectively). The average percentage of lumbar spine BMD change with and without exogenous lard, oil, and water showed increase of 0.51%, and 0.67%, and decrease of 1.02%, respectively. Using the phantom, BMD decreased with the placement of both lard (-0.002 g/cm², p=0.699) and water (-0.006 g/cm², p=0.153); however, there was no difference in BMD after oil placement.

CONCLUSION

These results suggest that in cases where changes in fat and ECF volume are similar, ECF exerts a greater influence than fat on DXA lumbar BMD measurements.

Novel equations to estimate lean body mass in maintenance hemodialysis patients

BACKGROUND

Lean body mass (LBM) is an important nutritional measure representing muscle mass and somatic protein in hemodialysis patients, for whom we developed and tested equations to estimate LBM.

STUDY DESIGN

A study of diagnostic test accuracy.

SETTING & PARTICIPANTS

The development cohort included 118 hemodialysis patients with LBM measured using dual-energy x-ray absorptiometry (DEXA) and near-infrared (NIR) interactance. The validation cohort included 612 additional hemodialysis patients with LBM measured using a portable NIR interactance technique during hemodialysis.

INDEX TESTS

3-month averaged serum concentrations of creatinine, albumin, and prealbumin; normalized protein nitrogen appearance; midarm muscle circumference (MAMC); handgrip strength; and subjective global assessment of nutrition.

REFERENCE TEST

LBM measured using DEXA in the development cohort and NIR interactance in validation cohorts.

RESULTS

In the development cohort, DEXA and NIR interactance correlated strongly (r = 0.94, P < 0.001). DEXA-measured LBM correlated with serum creatinine level, MAMC, and handgrip strength, but not with other nutritional markers. Three regression equations to estimate DEXA-measured LBM were developed based on each of these 3 surrogates and sex, height, weight, and age (and urea reduction ratio for the serum creatinine regression). In the validation cohort, the validity of the equations was tested against the NIR interactance-measured LBM. The equation estimates correlated well with NIR interactance-measured LBM (R² ≥ 0.88), although in higher LBM ranges, they tended to underestimate it. Median (95% confidence interval) differences and interquartile range for differences between equation estimates and NIR interactance-measured LBM were 3.4 (-3.2 to 12.0) and 3.0 (1.1-5.1) kg for serum creatinine and 4.0 (-2.6 to 13.6) and 3.7 (1.3-6.0) kg for MAMC, respectively.

LIMITATIONS

DEXA measurements were obtained on a nondialysis day, whereas NIR interactance was performed during hemodialysis treatment, with the likelihood of confounding by volume status variations.

CONCLUSIONS

Compared with reference measures of LBM, equations using serum creatinine level, MAMC, or handgrip strength and demographic variables can estimate LBM accurately in long-term hemodialysis patients.

The effect of peritoneal dialysate on DXA bone densitometry results in patients with end-stage renal disease

The bone mineral density of patients undergoing peritoneal dialysis (PD) is low compared to a healthy population. No studies have been conducted to investigate whether the presence of peritoneal dialysate affects dual-energy X-ray absorptiometry (DXA) results. We hypothesized that the presence of peritoneal dialysate would not affect the measurement of bone mineral density (BMD) or bone mineral content (BMC) in the spine. Thirty patients on PD had DXA scans of the lumbar spine and hip completed before and after the drainage of peritoneal dialysate. A paired t-test was used to compare the difference in area, BMC, and BMD before and after drainage of dialysate. A significant difference was found in the BMC of the spine before and after the drainage of dialyzate. We recommend that peritoneal dialyzate be removed prior to scanning patients on PD and that densitometry technologists should be observant about the presence of peritoneal dialysate.

Usefulness of different techniques for measuring body composition changes during weight loss in overweight and obese women

The objective was to compare measures from dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA) and anthropometry with a reference four-compartment model to estimate fat mass (FM) and fat-free mass (FFM) changes in overweight and obese women after a weight-loss programme. Forty-eight women (age 39.8 ± 5.8 years; weight 79·2 ± 11·8 kg; BMI 30·7 ± 3·6 kg/m2) were studied in an out-patient weight-loss programme, before and after the 16-month intervention. Women attended weekly meetings for the first 4 months, followed by monthly meetings from 4 to 12 months. Body composition variables were measured by the following techniques: DXA, anthropometry (waist circumference-based model; Antrform), BIA using Tanita (TBF-310) and Omron (BF300) and a reference four-compartment model. Body weight decreased significantly ( − 3·3 (sd3·1) kg) across the intervention. At baseline and after the intervention, FM, percentage FM and FFM assessed by Antrform, Tanita, BF300 and DXA differed significantly from the reference method (P ≤ 0·001), with the exception of FFM assessed by Tanita (baselineP = 0·071 and afterP = 0·007). DXA significantly overestimated the change in FM and percentage FM across weight loss ( − 4·5v. − 3·3 kg;P < 0·001 and − 3·7v. − 2·0 %;P < 0·001, respectively), while Antrform underestimated FM and percentage FM ( − 2·8v. − 3·3 kg;P = 0·043 and − 1·1v. − 2·0 %;P = 0·013) compared with the four-compartment model. Tanita and BF300 did not differ (P>0·05) from the reference model in any body composition variables. We conclude that these methods are widely used in clinical settings, but should not be applied interchangeably to detect changes in body composition. Furthermore, the several clinical methods were not accurate enough for tracking body composition changes in overweight and obese premenopausal women after a weight-loss programme.

Increased body mass index is not a reliable marker of good nutrition in hemodialysis patients

OBJECTIVE

The aim of the study was to assess the body fat (BF) composition in hemodialysis (HD) patients using anthropometry and bioelectrical impedance analysis (BIA) and investigate relationships between BIA-determined BF composition and nutritional parameters in different weight groupings.

DESIGN

Cross-sectional study.

SETTING

A tertiary-care university hospital.

METHODS

164 HD patients (M/F: 89/75, mean age: 48.4 +/- 15.8 years, mean HD duration: 58.2 +/- 42.6 months) were divided into three groups according to body mass index (BMI): normal weight (NW: BMI 18.5-24.9), overweight (OW: BMI 25-29.9), obese (OB, BMI > or = 30). Biochemical parameters and BF composition using anthropometry and foot-to-foot BIA were compared between three groups.

RESULTS

Ninety-six (59%) patients were NW, 40 (24%) were OW, and 28 (17%) were OB. Average mean skinfold thickness (p = 0.005), mid-arm circumference (p = 0.001), BF% (p = 0.001), and fat-free mass (FFM) (p = 0.03) were all significantly greater in the OB group than in the NW group. Compared to the NW patients, the OB group had significantly higher serum levels of glucose (p = 0.03), total cholesterol (p = 0.02), and triglycerides (p = 0.02), but significantly lower serum albumin (p = 0.05) and blood urea nitrogen (p = 0.05). The OB group also had significantly higher white blood cell count (p = 0.002) and serum CRP (p = 0.001) than the NW group.

CONCLUSIONS

The results suggest that BIA-determined BF composition is correlated with body mass index. In addition, obesity is associated with elevated CRP and white blood cell count and lower serum albumin level in HD patients.

Effect of equilibrated hydration changes on total body water estimates by bioelectrical impedance analysis

The present study was performed to determine how equilibrated fluctuations in hydration affected the validity of bioelectrical impedance analysis (BIA) for body composition assessment. Total body water (TBW) expansion was induced by a 4 d endurance trial and the subsequent water loss was obtained over the recovery period. Twelve healthy men exercised on a cycle and treadmill alternately for 5 h/d over 4 d at moderate intensity. TBW, fat mass (FM) and fat-free mass (FFM) were assessed 3 d before the trial (control), and on the first and eighth day of recovery (R1 and R8 respectively). TBW was evaluated by 2H dilution (TBW2H) as a reference method and by BIA (TBWBIA) at 100 kHz at the same time. TBW2H increased significantly between the control day and R1 by 1·87 (sd 1·11) litres (P=0·005) and TBWBIA by 1·38 (sd 1·56) litres (P=0·009). Both values returned to the control level on R8. For each period, TBW2H and TBWBIA did not differ significantly and were correlated (r2 0·85, P=0·0004 for the control day; r2 0·63, P=0·03 for R1; r2 0·75, P=0·02 for R8). Plasma Na concentration and osmolality did not differ between the control day, R1 and R8. FFM gain (1208 (sd 1983) g) and FM loss (−1168 (sd 906) g) between the control day and R1 were followed by a FFM decrease (−624 (sd 1281) g) and a FM increase (860 (sd 1212) g) between R1 and R8. As expected, these FFM and FM changes were significantly correlated with TBW variations. The present results provide evidence that BIA may be a useful method for estimating TBW when fluid shifts are equilibrated and electrolyte concentrations are unchanged. However, it is not a valid technique for assessing FM and FFM under these conditions.

Air displacement plethysmography can detect moderate changes in body composition

OBJECTIVES

To determine the sensitivity of air displacement plethysmography (APD) for evaluation of changes in body composition in normal subjects.

DESIGN

Comparison of measurements with and without oil or water loads.

SUBJECTS AND METHODS

Ten healthy volunteers were analyzed, without and with 1 l and 2 l of oil or water. The measured and true changes in fat mass and fat-free mass were compared by paired t-tests. A correlation study and a Bland & Altman procedure was performed on the 60 measurements of adiposity changes in 30 subjects carrying 0.5 l (n=8 x 2), 1 l (n=10 x 2) and 2 l (n=12 x 2) oil and water loads.

RESULTS

Fat-free mass increased when the 10 subjects were carrying water. When they carried oil, fat mass increased, however, a approximately 0.5 kg increase of fat-free mass was also detected. Two liters loads led to distinct changes: +1.49+/-0.59 kg fat and +0.50+/-0.60 kg fat-free with oil and +0.37+/-0.57 kg fat and +1.70+/-0.56 kg fat-free with water (both P<0.001). Mixed loads (+1 l oil and 1 l water) led to detect +0.85+/-0.48 kg fat and +1.09+/-0.45 kg fat-free (both P<0.005 vs without load). For the 30 subjects analyzed thrice, measured changes in fat and fat-free mass were slightly underestimated (-15%, NS) but correlated with the true changes. Measured changes in adiposity were correlated with the true changes, with no bias as indicated by the Bland & Altman procedure.

CONCLUSION

APD detects approximately 2 kg changes in fat or fat-free mass in small populations.

Dual-energy X-ray absorptiometry and body composition

PURPOSE OF REVIEW

Dual-energy X-ray absorptiometry is now widely adopted for the measurement of the fat, fat-free soft tissue and bone mineral compartments of the body. Whereas it is regarded by many as a reference technique for such measurements, it is not without limitations. Inter and intra-manufacturer differences have been areas of concern. This review focuses on recent literature addressing these areas and the issue of validity.

RECENT FINDINGS

Body composition measurements using newer generation dual-energy X-ray absorptiometry machines compared between different manufacturers and compared with earlier instruments continue to show differences that may be unacceptable, particularly for investigators upgrading their machines or involved in multicentre studies using different machines. In terms of validity, significant deviations at a group level are reported when compared with reference four-component models, and perhaps more importantly, wide limits of agreement are seen that are a concern for the interpretation of results at an individual level.

SUMMARY

It is important that investigators recognize the limitations of dual-energy X-ray absorptiometry technology in the interpretation of their results. There is a continuing need both for inter-machine comparisons and validation studies against accepted criterion methods, particularly as new software or technological changes are introduced. Such studies permit the development of translation equations for the cross-calibration of devices, and may be vital for cross-sectional studies. For longitudinal studies in many populations, dual-energy X-ray absorptiometry is without question a valuable technique for the measurement of compositional changes, both at the total body and regional levels.

Clinical applications of body composition measurements using DXA

Dual-energy X-ray absorptiometry (DXA) scanning was primarily developed for the diagnosis of osteoporosis and was initially applied to studies of the clinically important sites of the lumbar spine, femoral neck, and forearm. The rapid adoption of DXA has led to the development of different, competing generations of equipment. Improvements have been achieved through advances in X-ray generation and detection technology, modification of data acquisition protocols, and implementation of more sophisticated image analysis algorithms. As a result, DXA has been extended to allow the study of the total skeleton and its regional parts, as well as soft-tissue composition measurement. The three major components of the body: fat mass, lean mass, and bone mineral mass, can now be easily measured using a single whole body DXA scan with high precision and low scanning time. The comprehensive view of body composition provided by DXA makes it an attractive technique for a variety of clinical applications such as the prevention of cardiovascular and metabolic diseases, clinical management of different chronic diseases, and monitoring of the impact of treatment regimens on body tissues. In this article we review the contribution DXA has made to the understanding of body composition in clinical studies in adults.

Body composition and energy metabolism in chronic renal insufficiency

Malnutrition and wasting are important determinants of morbidity and mortality in patients with chronic renal failure on dialysis. The aim of this study was to determine body composition and energy metabolism in patients with chronic renal insufficiency before dialysis. We compared 15 patients (9 women and 6 men) with chronic renal failure (creatinine, 1.5 to 4.2 mg/dL) with 15 normal subjects pair-matched for sex, age (renal failure versus normal, 71 +/- 3 years versus 64 +/- 3 years), height (1.61 +/- 0.02 m versus 1.64 +/- 0.02 m), and weight (64.5 +/- 2.7 kg versus 66.4 +/- 1.5 kg). Body composition was measured by dual-energy x-ray absorptiometry, and total body water was measured by bioelectrical impedance. Energy metabolism was determined by indirect calorimetry. The average glomerular filtration rate for the patients with chronic renal insufficiency was 23.9 +/- 2.6 mL/min/1.73 m2. Lean body mass (41.1 +/- 2.0 kg versus 44.5 +/- 2.2 kg; P = 0.003) and bone mineral content (2.35 +/- 0.11 kg versus 2.72 +/- 0.12 kg; P = 0.007) were significantly lower in chronic renal insufficiency; however, fat body mass was the same (19.9 +/- 2.1 kg versus 19.1 +/- 1.4 kg; P = 0.68). Total body water was similar in renal failure (33.4 +/- 1.5 L versus 34.4 +/- 1.3 L; P = 0.13). Basal energy expenditure was significantly lower in chronic renal insufficiency (1,085 +/- 50 kcal/24 hours versus 1,280 +/- 54 kcal/24 hours; P = 0.02), even after adjustment for the differences in lean body mass. Daily caloric intake indicated energy intake was similar in the patients with chronic renal insufficiency and the controls. Patients with a relatively modest degree of chronic renal insufficiency are characterized by reduced lean body mass, bone mineral content, and basal energy expenditure. The determinants of lean body mass in chronic renal insufficiency require further investigation.

Change in muscle mass and muscle strength after a hip fracture: relationship to mobility recovery

BACKGROUND

Hip fracture in elderly persons has a serious impact on long-term physical function. This study determines the change in muscle strength and muscle mass after a hip fracture, and the associations between these changes and mobility recovery.

METHODS

Ninety community-dwelling women aged 65 years and older who had recently experienced a fracture of the proximal femur were included in the study. At 2 to 10 days after hospital admission, the women's grip strength, ankle dorsiflexion strength, and regional muscle mass (by dual-energy x-ray absorptiometry) were measured, and the prefracture level of independence for five mobility function items was assessed. All measurements were repeated at 12 months.

RESULTS

At follow-up, only 17.8% of the women had returned to their prefracture level of mobility function for all five items. Mobility function recovery was not related to change in skeletal muscle mass of the nonfractured leg or the arms. However, women who lost grip strength (mean loss of -28.7%, SD = 16.9%), or who lost ankle strength of the nonfractured leg (mean loss of -21.5%, SD = 14.7%), had a worse mobility recovery compared with those who gained strength (p = .04 and p = .09, respectively). In addition, chronic disease (p = .03), days hospitalized (p = .04), and self-reported hip pain (p = .07) were independent predictors of decline in mobility function.

CONCLUSIONS

The results suggest that loss of muscle strength, but not loss of muscle mass, is an independent predictor of poorer mobility recovery 12 months after a hip fracture. When confirmed by other studies, these findings may have implications for rehabilitation strategies after a hip fracture.

Comparison of methods for assessing body-composition changes over 1 y in postmenopausal women

BACKGROUND

Advances in dual-energy X-ray absorptiometry (DXA) software algorithms have improved the accuracy of this method for body-composition measurement.

OBJECTIVE

Our objective was to compare the utility of DXA, underwater weighing (UWW), and a multicomponent model (MC) for assessing changes in body composition.

DESIGN

: Previously sedentary women aged 40-66 y were randomly assigned to exercise training (ET; n = 36) and no exercise training (NT; n = 40). ET subjects exercised 3 d/wk; NT subjects remained sedentary. Changes in body mass, fat mass, and fat-free mass over 1 y were assessed by the 3 methods.

RESULTS

Correlations among methods were significant and large (0.73-0.97). Body weight did not change significantly in either group. In the ET group, fat-free mass increased significantly as assessed by DXA (0.7 +/- 1.0 kg) but changes assessed by MC and UWW were not significant. Changes in fat mass and percentage body fat in the ET group were not significant. SDs for changes in fat mass and percentage body fat, respectively, from DXA were 2.5 kg and 2.7%; for MC, 5.5 kg and 7.1%; and for UWW, 4.4 kg and 5.8%. In the NT group, changes in fat-free mass, fat mass, and percentage body fat were significant (P </= 0.02) as assessed by MC (fat-free mass, -1.5 +/- 3.7 kg; fat mass, 2.3 +/- 4.1 kg; percentage body fat, 2.8 +/- 4.7%) and UWW (fat-free mass, -1.1 +/- 2.5 kg; fat mass, 2.1 +/- 3.6 kg; percentage body fat, 2.5 +/- 3.5%), but changes by DXA were not significant (fat-free mass, 0.2 +/- 1.2 kg; fat mass, 1.0 +/- 3.9 kg; percentage body fat, 0.6 +/- 3.2%).

CONCLUSION

DXA was the most sensitive method for assessing small changes in body composition of postmenopausal women.

Validation of bioimpedance analysis as a measure of change in body cell mass as estimated by whole-body counting of potassium in adults

BACKGROUND

The body cell mass (BCM) is an important measure of macronutrient status, but measurements are difficult to obtain outside of sophisticated research laboratories. Bioimpedance analysis (BIA) is a simple technique that holds promise as a means of estimating body composition. The purpose of this study was to evaluate the ability of BIA to estimate changes in BCM as measured by whole body counting of 40K (TBK).

METHODS

Paired studies of BCM, including both TBK and BIA, were compared in 87 human immunodeficiency virus-positive subjects and in 62 healthy, weight-stable control adults. Potential errors in the predictions were examined.

RESULTS

BCM change by TBK and BIA correlated closely (r = .755). After accounting for errors related to repeat measures of TBK, the correlation coefficient was .784, with a standard error of the estimate of 1.24 kg. The differences between predicted and measured BCM change were consistent with a normal distribution. However, there was a systematic error in prediction, with BIA underpredicting the magnitudes of both gains and losses in BCM by TBK.

CONCLUSIONS

BIA is a useful surrogate for measuring changes in BCM in clinical circumstances. Because TBK assesses only intracellular potassium, whereas BIA reflects all intracellular cations, the underprediction of BCM change by BIA compared with TBK could be related to changes in intracellular potassium concentration as a result of malnutrition or its treatment.

Altered abdominal fat distribution and its association with the serum lipid profile in non-diabetic haemodialysis patients

BACKGROUND

Disturbances of lipid and carbohydrate metabolism may be associated with the distribution of abdominal adiposity. However, little is known about the alteration of abdominal adiposity and its association with the serum lipid profile in haemodialysis patients.

METHODS

We evaluated the distribution of abdominal adiposity by using computed tomography and examined its relationship with the serum lipid profile in 92 non-diabetic haemodialysis patients and 80 control subjects with normal renal function. Since the mean body mass index (BMI) and total body fat mass were significantly lower in the haemodialysis patients than in the control subjects, the subcutaneous abdominal fat area and the visceral fat area were standardized by body mass index and compared between the haemodialysis patients and the control subjects.

RESULTS

Mean subcutaneous fat area/body mass index (SFA/BMI) was significantly lower, and mean visceral fat area/body mass index (VFA/BMI) was significantly higher in the haemodialysis patients (SFA/BMI, 2.40+/-0.12; VFA/BMI, 2.28+/-0.15) than in the control subjects (SFA/BMI, 3.75+/-0.21, P<0.01; VFA/BMI, 1.65+/-0.15, P<0.01). Consequently, visceral fat area/ subcutaneous fat area ratio was significantly higher in the haemodialysis patients (1.05+/-0.07) than in the control subjects (0.46+/-0.04, P<0.01). A scattered plot of visceral fat area relative to BMI revealed that visceral fat area was higher in the haemodialysis patients than in the control subjects at any BMI level. A simple regression analysis showed that BMI, total body fat mass, subcutaneous fat area and visceral fat area were all associated with serum triglycerides and the atherogenic index, (total cholesterol-HDL cholesterol)/HDL cholesterol. Furthermore, a multiple regression analysis indicated that the visceral fat area was the best predictor for either the atherogenic index or triglycerides among these fat components.

CONCLUSIONS

These data indicate that haemodialysis patients exhibited a visceral fat accumulation irrespective of BMI, and this shift of abdominal adiposity might be associated with disturbance of the serum lipid profile in non-diabetic haemodialysis patients.

Dual-energy X-ray absorptiometry: a review

Dual-energy X-ray absorptiometry (DXA) has been recently used for body composition analysis in dialysis patients. It is based on the principle that X-rays passed through various body tissues have different attenuation and, therefore, can be differentiated. By using X-rays at two different energy levels, better tissue differentiation is possible compared with single energy systems. This article will review the evolution of DXA scanners and the role DXA has in assessing body composition in dialysis patients. Overall, this technique has excellent precision and holds promise for use in the serial evaluation of body composition and nutritional evaluation of dialysis patients.

Association of the serum leptin concentration with weight loss in chronic hemodialysis patients

Circulating leptin, which is partly cleared by the kidney, has been reported to increase with chronic renal failure and thus may play a role in the weight loss of patients with chronic renal failure. We investigated the association of body weight loss with the serum leptin concentration in Japanese hemodialysis patients. The relationship between serum leptin and the body mass index (BMI) or body fat mass was compared among 181 patients undergoing hemodialysis and 185 control subjects. There was no difference in the serum leptin concentration between the hemodialysis patients (HD) and controls (C) for either the men (3.9 +/- 0.2 ng/mL for HD, n=117; 3.9 +/- 0.3 ng/mL for C, n=89; NS) or women (8.9 +/- 1.2 ng/mL for HD, n=64; 7.4 +/- 0.5 ng/mL for C, n=96; NS), whereas BMI of the hemodialysis patients was significantly lower than that of the controls for both the men (20.1 +/- 0.2 kg/m2 for HD, 22.4 +/- 0.3 kg/m2 for C, P < 0.001) and women (19.2 +/- 0.3 kg/m2 for HD, 22.0 +/- 0.4 kg/m2 for C, P < 0.001). The serum leptin/body fat mass ratio was significantly correlated with the weight change of the patients during a follow-up evaluation period of 17 months (r = -0.37, P < 0.05 for men, n=27 and r = -0.53, P < 0.005 for women, n=28), indicating the possibility that a relatively high level of serum leptin had induced weight loss in the hemodialysis patients. The serum leptin/body fat mass ratio also showed a significant inverse correlation with the duration of hemodialysis (r = -0.31, P < 0.05 for men and r = -0.49, P < 0.05 for women). A multiple regression analysis indicated that the body fat mass was significantly correlated with serum leptin concentration, whereas the fat distribution did not have any relationship with leptin. These data indicate that a high level of serum leptin relative to the body fat mass might be associated with weight loss in long-term hemodialysis patients. The serum leptin level relative to the body fat mass also seems to have been affected by the duration of hemodialysis.

Is there evidence for an age-related reduction in metabolic rate?

To determine whether the age-related reduction in basal metabolic rate (BMR) is explained by a quantitative and/or qualitative change in the components of lean tissue, we conducted a cross-sectional study in groups of young (n = 38, 18-35 yr) and older (n = 24, 50-77 yr) healthy individuals. BMR was measured by indirect calorimetry. Body composition was obtained by using dual-energy X-ray absorptiometry (DEXA), which permitted four compartments to be quantified [bone mineral mass, fat mass (FM), appendicular lean tissue mass (ALTM), and nonappendicular lean tissue mass (NALTM)]. Absolute BMR and ALTM were lower, whereas FM was significantly higher in the older, compared with young, subjects. BMR, adjusted for differences in FM, ALTM, and NALTM, was significantly lower in the older subjects by 644 kJ/day. In separate regression analyses of BMR on body compartments, older subjects had significantly lower regression coefficients for ALTM and NALTM, compared with young subjects. Hence, the age-related decline in BMR is partly explained by a reduction in the quantity, as well as the metabolic activity, of DEXA-derived lean tissue components.

Relationships among liver and kidney volumes, lean body mass and drug clearance

AIMS

To determine whether lean body mass (LBM), a possible surrogate of liver and kidney volumes, correlates with hepatic and renal drug clearances.

METHODS

Twenty-one disease-free patients with a history of cancer and with normal hepatic and renal function were studied. Salivary pharmacokinetics of oral antipyrine (1200 mg) and 24 h creatinine clearance were determined following the determination of LBM by dual energy X-ray absorptiometry and the determination of liver and kidney volumes by helical CT scanning.

RESULTS

Liver volume correlated with LBM (r2=0.21, P=0.04), body surface area (BSA) (r2=0.54, P<0.001), and total body weight (TBW) (r2=0.61, P<0.001). Kidney volume correlated with LBM (r2=0.49, P<0.001), BSA (r2=0.43, P=0.002) and TBW (r2=0.24, P=0.03). Stepwise multiple regression analysis, incorporating the independent variables of age, height, weight, sex, BSA, LBM, alcohol consumption, smoking status and liver volume and the dependent variable antipyrine clearance, indicated that LBM was the only independent correlate of antipyrine clearance. A stepwise multiple regression analysis with kidney volume in the independent variables, and creatinine clearance as dependent variable, showed that kidney volume and age were the only independent correlates of creatinine clearance. A nomogram using serum creatinine and LBM was comparable with the Cockcroft and Gault nomogram in calculating creatinine clearance.

CONCLUSIONS

Of the anthropometric variables tested, LBM was the only determinant of antipyrine clearance, but this was not due to a relationship between LBM and liver volume. By contrast, the relationship between creatinine clearance and LBM appeared to be due to a relationship between LBM and kidney volume.

Androgen effects on body composition and muscle function: implications for the use of androgens as anabolic agents in sarcopenic states

Testosterone-induced nitrogen retention in castrated male animals, eunuchoidal men, pre-pubertal boys and women, and the sex-related differences in the size of the muscles between male and female animals, have been cited as evidence that testosterone has anabolic effects. Recent studies have reported that replacement doses of testosterone in hypogonadal men and supraphysiological doses in eugonadal men increase fat-free mass, muscle size and strength. These effects have provided the rationale for exploring these anabolic applications in sarcopenic states. Although emerging data demonstrate modest gains in fat-free mass in HIV-infected men given replacement doses of testosterone, we do not know whether testosterone supplementation can produce clinically meaningful changes in muscle function and disease outcome in patients with wasting disorders.

Comparison of different techniques to measure body composition in moderately active adolescents

OBJECTIVE

To evaluate the differences in the estimate of body fat percentage (%FM) and the amount (kg) of fat free mass (FFM) by different methods in 26 moderately active adolescents very similar in age, body fatness, and training status.

METHODS

Mean (SD) age was 16.7 (0.9) years, height was 177.0 (5.1) cm, and weight 68.0 (5.2) kg. %FM was assessed using dual-energy x ray absorptiometry (DXA) and two skinfold prediction equations: that of Slaughter et al (%FM Sla) and that of Deurenberg et al (%FM Deu). In the same way, FFM was measured using DXA and different impedance equations: those of Suprasongsin et al (FFM Sup), Schaefer et al (FFM Sch), Houtkooper et al (FFM Hou), and Deurenberg et al (FFM Deu). To determine the interchangeability of the different methods of measuring %FM and FFM, one way analysis of variance, standard error (SE), and coefficient of variation (CV%) ((SD/mean) x 100) were used.

RESULTS

On average, no significant statistical differences were observed between the values determined for %FM: DXA value, 11.7 (5.4%); %FM Sla, 10.9 (4.0)%; %FM Deu, 11.5 (2.3)%. On the other hand, SE and CV% between each pair of the three methods used showed very large variability. With regard to the measurement or prediction of FFM, the mean value measured by DXA was significantly higher than that predicted by the equation of Sch (+7.2 kg, p < 0.001), Deu (+3.2 kg, p < 0.001), and Hou (+2.6 kg, p < 0.001), whereas it was lower than that predicted by the equation of Sup (-1.6 kg, p < 0.05). The Hou and Deu values were the only two that, on average, did not differ in a statistically significant way, although they showed the highest CV%.

CONCLUSIONS

In our sample of moderately active adolescents the estimated values for %FM and FFM appear to be highly dependent on method.

Effects of orthotopic liver transplantation on body composition

AIMS/BACKGROUND

The effects of orthotopic liver transplantation on body composition are unclear. We aimed to assess changes in body composition after transplantation using dual energy x-ray absorptiometry and total body potassium.

METHODS

Dual energy x-ray absorptiometry and total body potassium counting to assess muscle mass were performed in 55 patients before and up to 24 months after liver transplantation and the results expressed as paired data before and at time intervals after transplantation.

RESULTS

The results showed that total body weight fell by 3.6 +/- 1.3 kg (p < 0.02) at 1 month, with a maximal fall in lean tissue mass at 2-5 months of 4.8 +/- 1.2 kg (p < 0.003). Thereafter, no change in lean tissue mass was recorded, although there were increases at 12 and 24 months of total body weight (11.5 +/- 2.4 kg, 7.8 +/- 3.1 kg; p < 0.03, respectively) and fat mass (12.9 +/- 2.2 and 10.5 +/- 2.7 kg; p < 0.003). A fall in total body potassium was seen at 1 month (118 +/- 12 mmol; p < 0.003) and 2-5 months (176 +/- 9.9 mmol; p < 0.03), which mirrored the fall in lean mass.

CONCLUSIONS

After liver transplantation there is an initial fall in body weight due to a loss of lean mass. Lean mass does not recover after transplantation, although there is an increase in fat mass that leads to the observed increase in total body weight.

Dual-energy X-ray absorptiometry: fat estimation errors due to variation in soft tissue hydration

Dual-energy X-ray absorptiometry (DXA) is rapidly gaining acceptance as a reference method for analyzing body composition. An important and unresolved concern is whether and to what extent variation in soft tissue hydration causes errors in DXA fat estimates. The present study aim was to develop and validate a DXA physical hydration model and then to apply this model by simulating errors arising from hypothetical overhydration states. The DXA physical hydration model was developed by first linking biological substance elemental content with photon attenuation. The validated physical model was next extended to describe photon attenuation changes anticipated when predefined amounts of two known composition components are mixed, as would occur when overhydration develops. Two overhydration models were developed in the last phase of study, formulated on validated physical models, and error was simulated for fluid surfeit states. Results indicate that systematic errors in DXA percent fat arise with added fluids when fractional masses are varied as a percentage of combined fluid + soft tissue mass. Three independent determinants of error magnitude were established: elemental content of overhydration fluid, fraction of combined fluid + soft tissue as overhydration fluid, and initial soft tissue composition. Small but systematic and predictable errors in DXA soft tissue composition analysis thus can arise with fluid balance changes.

Preliminary evidence that DEXA provides an accurate assessment of body composition

It was previously found that dual-energy X-ray absorptiometry (DEXA) underestimated central body fat. The purposes of this study were to determine whether an updated version (enhanced version 5.64) of the analysis program corrected this problem (experiment 1) and to compare body composition assessed by DEXA and hydrodensitometry (HD) in women (n = 225) and men (n = 110) across a 21- to 81-yr age range (experiment 2). For experiment 1, 10 subjects underwent DEXA procedures in a control condition and with packets of lard positioned over either the thighs or the truncal region. DEXA accurately quantified the additional mass as approximately 96% fat, regardless of position. For experiment 2, DEXA yielded higher (P < 0.001) estimates of fatness than did HD (32.1 +/- 12.0 vs. 31.2 +/- 10.1%). The mean difference between the two methods was similar in young, middle-aged, and older subjects, but was different in men (HD-DEXA, 1.6 +/- 3.4% of body wt) than in women (-2.1 +/- 3.8% of body wt). Correcting the density of fat-free mass for variance in the bone mineral fraction of fat-free mass reduced the difference between the methods in men from 1.6 +/- 3.4 to -0.7 +/- 2.9% but widened it in women from -2.1 +/- 3.8 to -3.5 +/- 3.4%. A second correction procedure that adjusted for variance in water, protein, and mineral fractions of fat-free mass eliminated the differences in estimates of fat content by DEXA and HD in both men (21.1 +/- 9.3 vs. 20.6 +/- 8.4%, respectively) and women (37.5 +/- 9.3 vs. 36.8 +/- 8.0%, respectively). These results provide encouraging, but not definitive, evidence that the assessment of body composition by DEXA is accurate under the specified conditions.

Protein catabolic rate over lean body mass ratio: a more rational approach to normalize the protein catabolic rate in dialysis patients

Protein catabolic rate (PCR), equivalent to dietary protein intake in "stable" dialysis patients, is widely accepted as a marker of their protein nutritional status. PCR is usually established from urea generation rate using urea kinetic modeling (UKM), but the normalizing factor is still a matter of controversy. By convention, PCR is expressed in grams of protein degraded daily divided by the dry body weight (BW) (nPCRBW). To be valid, this implies that dry BW is close to ideal BW and that body composition is preserved with a lean body mass (LBM) over BW ratio near 0.73. Such conditions being infrequently found in dialysis patients, it has been proposed to normalize PCR to ideal BW or to total body water, but these correction factors are not really appropriate. A more rational approach would be to express PCR as the ratio of protein degraded to the kilograms of LBM (nPCRLBM), thus offering the main advantage of directly coupling PCR to changes in protein or nitrogen reserve. In this study, we developed a combined kinetic model of urea and creatinine applied to the midweek dialysis cycle in 66 end-stage renal disease (ESRD) patients. UKM provided Kt/V and PCR, whereas creatinine kinetic modeling (CKM) was used to calculate LBM. Thirty-four patients with a preserved LBM (LBM/dry BW ratio equal to or greater than 0.70; mean ratio, 0.81 +/- 0.11) and with a dry/ideal BW ratio of 1.01 +/- 0.16 had a mean PCR of 1.14 +/- 0.30 g/kg/24 h when normalized to BW (nPCRBW) and of 1.40 +/- 0.30 g/kg/24 h when normalized to LBM (nPCRLBM). In the 32 patients with a reduced LBM (LBM/dry BW ratio, below 0.70; mean ratio, 0.60 +/- 0.09) and dry/ideal BW ratio of 1.11 +/- 0.23, the mean nPCRBW was 0.99 +/- 0.31 g/kg/24 h, whereas nPCRLBM was 1.62 +/- 0.32 g/kg/24 h. For both subgroups, Kt/V was similar, with mean values of 1.76 +/- 0.34 and 1.69 +/- 0.27. Normalizing PCR to LBM offers a double benefit: it compensates for the error induced by abnormal body composition (eg, obese patients) and permits PCR to be adjusted for the decrease in LBM that occurs with age. We propose nPCRLBM as a more rational index to express PCR in dialysis patients.

Proportional changes in body fluid with hemodialysis evaluated by dual-energy X-ray absorptiometry and transthoracic bioimpedance with particular emphasis on the thoracic region

Alterations in body composition during extracorporeal hemodialysis (HD) were investigated in 12 hemodialysis patients (9 males and 3 females, mean age 50 +/- 15 years) with a mean ultrafiltration of 2.6 +/- 1.0 L. Analysis was performed using a dual-energy x-ray absorptiometry technique (DXA), which measures 3 principal components of the body: fat mass (FM): lean body mass (LBM), i.e., all soft tissues excluding fat; and bone mineral content (BMC). These 3 components were calculated for the whole body and for different body regions (namely, the thorax, trunk, lower limbs, and upper limbs). The thoracic cage region could be defined manually, separately from the trunk, and its tissue composition was calculated. DXA analysis was performed concomitant with a measurement of the basal thoracic impedance (TFI) by bioimpedance cardiography prior to and 1 h after dialysis. We found a significant decrease in the total LBM, from 55.8 +/- 8.8 to 53.3 +/- 9.3 kg (p < 0.05), but no change in either the FM or BMC. Moreover, there was a disproportional reduction in the LBM in different regions, being significantly greater in the thorax (7.47 +/- 3.7%) than in the other body regions (trunk 4.3 +/- 2.0%, lower limbs 5.4 +/- 2.1%, and upper limbs 4.7 +/- 1.5%). Regarding bioimpedance, a stronger significant correlation was detected between the percentage changes in the TFI and the changes in thoracic fluid (r = 0.80, p < 0.01) than between the changes in the TFI and the changes in the total body fluid (r = 0.63, p < 0.01). The absolute values of the TFI were also significantly and negatively correlated to the thoracic lean mass to fat mass ratio, both before and after HD (r = 0.82, p < 0.001 and r = 0.86, p < 0.001, respectively). In conclusion, DXA is a very sensitive technique to detect fluid changes during HD in the thorax when the thoracic cavity is defined as a region of interest as well as for the whole body. The data also indicate an extracellular compartmental imbalance between different regions with a significantly greater change in the thoracic region. Transthoracic bioimpedance is a useful technique for evaluating the HD induced changes in the thoracic fluid, rather than total body fluid.

Body composition changes in chronic hemodialysis patients before and after hemodialysis as assessed by dual-energy x-ray absorptiometry

The aim of this study was to investigate the effect of hemodialysis on body composition assessment by dual-energy x-ray absorptiometry (DEXA). Seventeen patients with chronic renal failure who were on a regular hemodialysis schedule were studied. Body weight and body composition were assessed immediately before and approximately 1 hour after a typical hemodialysis session. Body weight was assessed by means of an electronic balance. Body composition measurements were made by DEXA. Whole-body and subtotal (head and neck excluded) analysis assessed the following parameters: body weight, bone mineral density (BMD), bone mineral content (BMC), and fat (FTM) and lean (LTM) tissue mass. BMC, FTM, and LTM were estimated separately for the trunk, arms, and legs. The mean body weight reduction after hemodialysis was 2.8 +/- 1.1 kg (mean +/- SD). Concerning whole-body analysis, no change was observed in mean BMC and FTM after hemodialysis. On the contrary, a significant reduction was observed in mean body weight as assessed by DEXA (before hemodialysis, 65.0 +/- 11.4 kg; after, 62.2 +/- 10.9 kg, P = .0003), as well as in mean LTM (before hemodialysis, 42.7 +/- 9.4 kg; after, 39.7 +/- 9.0 kg, P = .0003). Similar results were obtained from subtotal and regional analysis. Body weight changes as measured by the electronic balance exhibited a strong positive correlation with the changes in both body weight and LTM as assessed by DEXA (r = .989, standard error of the estimate [SEE] = 0.167 kg and r = .941, SEE = 0.382 kg, respectively, P < .0001). It is concluded that gravimetric changes induced by hemodialysis are highly correlated with LTM changes and are not associated with changes in BMC or FTM estimated by DEXA.

Comparison of body composition in black and white premenopausal women

We examined 23 pairs of black and white premenopausal women to determine whether there were ethnic differences in body composition. The pairs were matched on weight and height. Each woman had measurements of total body water taken by a tritiated water dilution technique, total body nitrogen, and total body carbon by neutron-activation, mineral ash by dual x-ray absorptiometry, and body potassium by whole body counting. Differences between blacks and whites were compared with the use of both the two-compartment and four-compartment models. The two-compartment model showed that in premenopausal black and white women of similar age, heights, and weights, blacks had significantly more lean mass. The four-compartment model resulted in similar conclusions. The black women had larger protein, mineral, and water compartments and less fat than whites. It may be that body weight measurements as an indicator of obesity should be adjusted for black versus white women.