Correcting Posterior Paraspinal Muscle Computed Tomography Density for Intravenous Contrast Material Independent of Sex and Vascular Phase.

PURPOSE: Intravenous contrast poses challenges to computed tomography (CT) muscle density analysis. We developed and tested corrections for contrast-enhanced CT muscle density to improve muscle analysis and the utility of CT scans for the assessment of myosteatosis. MATERIALS AND METHODS: Using retrospective images from 240 adults who received routine abdominal CT imaging from March to November 2020 with weight-based iodine contrast, we obtained paraspinal muscle density measurements from noncontrast (NC), arterial, and venous-phase images. We used a calibration sample to develop 9 different mean and regression-based corrections for the effect of contrast. We applied the corrections in a validation sample and conducted equivalence testing. RESULTS: We evaluated 140 patients (mean age 52.0 y [SD: 18.3]; 60% female) in the calibration sample and 100 patients (mean age 54.8 y [SD: 18.9]; 60% female) in the validation sample. Contrast-enhanced muscle density was higher than NC by 8.6 HU (SD: 6.2) for the arterial phase (female, 10.4 HU [SD: 5.7]; male, 6.0 HU [SD:6.0]) and by 6.4 HU [SD:8.1] for the venous phase (female, 8.0 HU [SD: 8.6]; male, 4.0 HU [SD: 6.6]). Corrected contrast-enhanced and NC muscle density was equivalent within 3 HU for all correctionns. The -7.5 HU correction, independent of sex and phase, performed well for arterial (95% CI: -0.18, 1.80 HU) and venous-phase data (95% CI: -0.88, 1.41 HU). CONCLUSIONS: Our validated correction factor of -7.5 HU renders contrast-enhanced muscle density statistically similar to NC density and is a feasible rule-of-thumb for clinicians to implement.

Small-Scale Randomized Controlled Trial to Explore the Impact of ß-Hydroxy-ß-Methylbutyrate Plus Vitamin D3 on Skeletal Muscle Health in Middle Aged Women.

ß-Hydroxy-ß-methylbutyrate (HMB), a leucine metabolite, can increase skeletal muscle size and function. However, HMB may be less effective at improving muscle function in people with insufficient Vitamin D3 (25-OH-D < 30 ng/mL) which is common in middle-aged and older adults. Therefore, we tested the hypothesis that combining HMB plus Vitamin D3 (HMB + D) supplementation would improve skeletal muscle size, composition, and function in middle-aged women. In a double-blinded fashion, women (53 ± 1 yrs, 26 ± 1 kg/m2, n = 43) were randomized to take placebo or HMB + D (3 g Calcium HMB + 2000 IU D per day) during 12 weeks of sedentary behavior (SED) or resistance exercise training (RET). On average, participants entered the study Vitamin D3 insufficient while HMB + D increased 25-OH-D to sufficient levels after 8 and 12 weeks. In SED, HMB + D prevented the loss of arm lean mass observed with placebo. HMB + D increased muscle volume and decreased intermuscular adipose tissue (IMAT) volume in the thigh compared to placebo but did not change muscle function. In RET, 12-weeks of HMB + D decreased IMAT compared to placebo but did not influence the increase in skeletal muscle volume or function. In summary, HMB + D decreased IMAT independent of exercise status and may prevent the loss or increase muscle size in a small cohort of sedentary middle-aged women. These results lend support to conduct a longer duration study with greater sample size to determine the validity of the observed positive effects of HMB + D on IMAT and skeletal muscle in a small cohort of middle-aged women.

Corrigendum: Myosteatosis as a Shared Biomarker for Sarcopenia and Cachexia Using MRI and Ultrasound.

[This corrects the article DOI: 10.3389/fresc.2022.896114.].

Myosteatosis as a Shared Biomarker for Sarcopenia and Cachexia Using MRI and Ultrasound.

Purpose: Establish bedside biomarkers of myosteatosis for sarcopenia and cachexia. We compared ultrasound biomarkers against MRI-based percent fat, histology, and CT-based muscle density among healthy adults and adults undergoing treatment for lung cancer. Methods: We compared ultrasound and MRI myosteatosis measures among young healthy, older healthy, and older adults with non-small cell lung cancer undergoing systemic treatment, all without significant medical concerns, in a cross-sectional pilot study. We assessed each participant's rectus femoris ultrasound-based echo intensity (EI), shear wave elastography-based shear wave speed, and MRI-based proton density fat-fraction (PDFF). We also assessed BMI, rectus femoris thickness and cross-sectional area. Rectus femoris biopsies were taken for all older adults (n = 20) and we analyzed chest CT scans for older adults undergoing treatment (n = 10). We determined associations between muscle assessments and BMI, and compared these assessments between groups. Results: A total of 10 young healthy adults, 10 older healthy adults, and 10 older adults undergoing treatment were recruited. PDFF was lower in young adults than in older healthy adults and older adults undergoing treatment (0.3 vs. 2.8 vs. 2.9%, respectively, p = 0.01). Young adults had significantly lower EI than older healthy adults, but not older adults undergoing treatment (48.6 vs. 81.8 vs. 75.4, p = 0.02). When comparing associations between measures, PDFF was strongly associated with EI (ρ = 0.75, p < 0.01) and moderately negatively associated with shear wave speed (ρ = -0.49, p < 0.01) but not BMI, whole leg cross-sectional area, or rectus femoris cross-sectional area. Among participants with CT scans, paraspinal muscle density was significantly associated with PDFF (ρ = -0.70, p = 0.023). Histological markers of inflammation or degradation did not differ between older adult groups. Conclusion: PDFF was sensitive to myosteatosis between young adults and both older adult groups. EI was less sensitive to myosteatosis between groups, yet EI was strongly associated with PDFF unlike BMI, which is typically used in cachexia diagnosis. Our results suggest that ultrasound measures may serve to determine myosteatosis at the bedside and are more useful diagnostically than traditional weight assessments like BMI. These results show promise of using EI, shear wave speed, and PDFF proxies of myosteatosis as diagnostic and therapeutic biomarkers of sarcopenia and cachexia.

The effect of computed tomography parameters on sarcopenia and myosteatosis assessment: a scoping review.

Computed tomography (CT) is a valuable assessment method for muscle pathologies such as sarcopenia, cachexia, and myosteatosis. However, several key underappreciated scan imaging parameters need consideration for both research and clinical use, specifically CT kilovoltage and the use of contrast material. We conducted a scoping review to assess these effects on CT muscle measures. We reviewed articles from PubMed, Scopus, and Web of Science from 1970 to 2020 on the effect of intravenous contrast material and variation in CT kilovoltage on muscle mass and density. We identified 971 articles on contrast and 277 articles on kilovoltage. The number of articles that met inclusion criteria for contrast and kilovoltage was 11 and 7, respectively. Ten studies evaluated the effect of contrast on muscle density of which nine found that contrast significantly increases CT muscle density (arterial phase 6-23% increase, venous phase 19-57% increase, and delayed phase 23-43% increase). Seven out of 10 studies evaluating the effect of contrast on muscle area found significant increases in area due to contrast (≤2.58%). Six studies evaluating kilovoltage on muscle density found that lower kilovoltage resulted in a higher muscle density (14-40% increase). One study reported a significant decrease in muscle area when reducing kilovoltage (2.9%). The use of contrast and kilovoltage variations can have dramatic effects on skeletal muscle analysis and should be considered and reported in CT muscle analysis research. These significant factors in CT skeletal muscle analysis can alter clinical and research outcomes and are therefore a barrier to clinical application unless better appreciated.

Combination of DXA and BIS Predicts Jump Power Better Than Traditional Measures of Sarcopenia.

Traditional diagnostic criteria for sarcopenia use dual-energy X-ray absorptiometry (DXA)-measured appendicular lean mass (ALM), normalized to height (ALM/ht2) or body mass index (ALM/BMI) to define low muscle mass. However, muscle function declines with aging before the loss of muscle mass is detected by ALM. This is likely due, in part, to qualitative muscle changes such as extracellular and intracellular fluid compartment shifts uncaptured by DXA. We propose combining bioimpedance spectroscopy (BIS), which estimates extracellular and intracellular compartment volume, with DXA to more accurately predict muscle function. This combination may help incorporate muscle quality, thereby improving sarcopenia diagnosis. We cross-sectionally analyzed data from 248 Black and White participants aged 25 to 75 years from the Midlife in the United States Refresher Cohort. We proposed two novel muscle measures: ALM corrected by the BIS-derived whole-body extracellular to intracellular fluid ratio (E/I) and leg lean mass (LLM) corrected by leg-specific E/I, creating (ALM/(E/I)W) and (LLM/(E/I)L), respectively. We compared the associations of traditional muscle measures, ALM/(E/I)W, and LLM/(E/I)L, with grip strength and lower limb power using jumping mechanography. LLM/(E/I)L explained jump power best at R 2 = 0.803 compared with ALM/(E/I)W (p < 0.0001) and all other measures. ALM/(E/I)W explained jump power second best (R 2 = 0.759) but not significantly better than traditional muscle measures. No muscle measure performed better than covariates when predicting handgrip strength. LLM/(E/I)L outperformed ALM/ht2 and ALM/BMI when predicting jump power. We propose LLM/(E/I)L is a powerful and clinically relevant method that accounts for muscle quality. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Nutrition Status and Health-Related Quality of Life Among Outpatients With Advanced Head and Neck Cancer.

This pilot study evaluated nutrition status and health-related quality of life (HRQOL) outcomes among outpatients with head and neck cancer (HNC). Data were collected from 19 patients (18 males, 1 female) during 3 time points: once before chemoradiotherapy (CRT) initiation and 1 and 3 months after CRT. Nutrition status was evaluated using the Scored Patient-Generated Subjective Global Assessment (PG-SGA). Malnutrition was defined as PG-SGA stage B (moderate/suspected malnutrition) or stage C (severely malnourished). HRQOL was assessed through the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) and its HNC-specific module (QLQ-H&N35). We found that well-nourished patients reported having fewer issues with pain, fatigue, appetite loss, chewing, sticky saliva, coughing, and social eating than those categorized as malnourished (P < .05). The association between the global quality-of-life score and PG-SGA score was statistically significant but weak in strength (r = -0.37, P = .012). Although PG-SGA identified 70% as either moderately or severely malnourished before treatment initiation, the mean body mass index was in the overweight category (29 ± 5 kg/m2 ). Compared with pretreatment, patients reported more severe problems with chewing, swallowing, sticky saliva, dry mouth, speech, social eating, and taste and smell sensations at 1-month follow-up, although issues with dry mouth persisted 3 months post treatment (P = .003). In conclusion, malnourished patients reported having worse HRQOL symptoms compared with well-nourished patients. Routine nutrition and psychosocial assessment through PG-SGA and EORTC tools might help identify patients in need of nutrition and psychosocial care.

Combination of DXA and BIS body composition measurements is highly correlated with physical function-an approach to improve muscle mass assessment.

RATIONALE: Fluid volume estimates may help predict functional status and thereby improve sarcopenia diagnosis. MAIN RESULT: Bioimpedance-derived fluid volume, combined with DXA, improves identification of jump power over traditional measures. SIGNIFICANCE: DXA-measured lean mass should be corrected for fluid distribution in older populations; this may be a surrogate of muscle quality. PURPOSE: Sarcopenia, the age-related loss of muscle mass and function, negatively impacts functional status, quality of life, and mortality. We aimed to determine if bioimpedance spectroscopy (BIS)-derived estimates of body water compartments can be used in conjunction with dual-energy X-ray absorptiometry (DXA) measures to aid in the prediction of functional status and thereby, ultimately, improve the diagnosis of sarcopenia. METHODS: Participants (≥ 70 years) had physical and muscle function tests, DXA, and BIS performed. Using a BMI correction method, intracellular water (ICWc), extracellular water (ECWc), and ECWc to ICWc (E/Ic) ratio was estimated from standard BIS measures. Jump power was assessed using jump mechanography. RESULTS: The traditional measure used to diagnose sarcopenia, DXA-derived appendicular lean mass (ALM) corrected for height (ALM/ht2), was the least predictive measure explaining jump power variability (r2 = 0.31, p < 0.0001). The best measure for explaining jump power was a novel variable combining DXA ALM and BIS-derived E/Ic ratio (ALM/(E/Ic); r2 = 0.70, p < 0.0001). ALM/(E/Ic) and ICWc had the highest correlation with jump power and grip strength, specifically jump power (r = 0.84 and r = 0.80, respectively; p < 0.0001). CONCLUSIONS: The creation of a novel variable (ALM/(E/Ic)) improved the ability of DXA to predict jump power in an older population. ALM/(E/Ic) substantially outperformed traditional lean mass measures of sarcopenia and could well be an improved diagnostic approach to predict functional status. DXA-measured ALM should be corrected for fluid distribution, i.e., ALM/(E/Ic); this correction may be considered a surrogate of muscle quality.

Impact of Software Selection and ImageJ Tutorial Corrigendum on Skeletal Muscle Measures at the Third Lumbar Vertebra on Computed Tomography Scans in Clinical Populations.

BACKGROUND: There is growing interest in computed tomography (CT) measures of skeletal muscle cross-sectional area (CSA) for nutrition assessment. Multiple software programs are available, but little work has been done comparing programs. We aimed to determine if CT-derived measures of skeletal muscle CSA at the level of the L3 are influenced by the software program used. We also demonstrate the importance of the ImageJ corrigendum published in this journal. METHODS: Two software programs, National Institutes of Health ImageJ and Tomovision sliceOmatic, were compared. ImageJ measures were obtained using both the original tutorial and corrigendum instructions. Skeletal muscle CSA at the level of the L3 was measured in advanced heart failure and head and neck cancer populations by 3 different investigators. Intraclass correlation coefficients were used to calculate intrarater and interrater reliability. Bland-Altman analysis was used to assess agreement. RESULTS: Both software programs yielded excellent intrarater and interrater reliability scores (intraclass correlation coefficients, 0.985-1.000). The overall mean difference (ImageJ tutorial with corrigendum - sliceOmatic) for the entire sample (N = 51) was found to be 1.53 cm2 (95% CI, 0.59-2.47 cm2 ). The overall mean difference (ImageJ corrected - original) for the entire sample (N = 51) was found to be -11.35 cm2 (95% CI, -12.75 to -9.95 cm2 ). CONCLUSION: Measures of skeletal muscle CSA at the L3 were found to be ∼1.53 cm2 higher with ImageJ than sliceOmatic. This difference was not found to affect interpretation against a published cut point. The importance of accounting for the ImageJ tutorial corrigendum was shown to be clinically significant when applied to published cut points.

Diagnosing clinical malnutrition: Perspectives from the past and implications for the future.

This review, intended for both researchers and clinicians, provides a history of the definition of clinical malnutrition. Despite global efforts, we remain without one clear, objective, internationally accepted definition; clarity in this regard will ultimately improve our evaluation and monitoring of nutritional status to achieve optimal patient outcomes. In this review we explore the development of the term malnutrition and its diagnosis and application in the setting of acute and chronic disease. We begin in the second century A.D. with the work of the Greek physician Galen who is credited as the first to apply the term marasmus to characterize three categories of malnutrition, which are surprisingly similar to components of current international definitions. We then highlight significant developments over the next 2000 years culminating in our current application of the clinical diagnosis of malnutrition. A perspective on historical practices may inform current efforts toward a global definition and diagnosis of malnutrition.

Malnutrition Identified by the Academy of Nutrition and Dietetics and American Society for Parenteral and Enteral Nutrition Consensus Criteria and Other Bedside Tools Is Highly Prevalent in a Sample of Individuals Undergoing Treatment for Head and Neck Cancer.

BACKGROUND: Using the Academy of Nutrition and Dietetics and American Society for Parenteral and Enteral Nutrition (Academy/ASPEN) Consensus malnutrition definition, we estimated malnutrition prevalence in a sample of individuals with head and neck cancer (HNC) and compared it with the Patient-Generated Subjective Global Assessment (PG-SGA). We also investigated the utility of the 50-kHz phase angle (PA) and 200-kHz/5-kHz impedance ratio (IR) to identify malnutrition. MATERIALS AND METHODS: Nineteen individuals (18 males, 1 female) scheduled to undergo chemoradiotherapy were seen at 5 time points during and up to 3 months after treatment completion. Multiple-frequency bioelectrical impedance analysis, PG-SGA, nutrition-focused physical examination, anthropometry, dietary intake, and handgrip strength data were collected. RESULTS: Using the Consensus, 67% were found to be malnourished before treatment initiation; these criteria diagnosed malnutrition with overall good sensitivity (94%) and moderate specificity (43%) compared with PG-SGA. Over all pooled observations, "malnourished" (by Consensus but not PG-SGA category) had a lower mean PA (5.2 vs 5.9; P = .03) and higher IR (0.82 vs 0.79; P = .03) than "well-nourished" categorizations, although the clinical relevance of these findings is unclear. PA and IR were correlated with higher PG-SGA score (r = -0.35, r = 0.36; P < .01) and handgrip strength (r = 0.48, r = -0.47; P < .01). CONCLUSION: The Academy/ASPEN Consensus and the PG-SGA were in good agreement. It is unclear whether PA and IR can be used as surrogate markers of nutrition status or muscle loss.

Protein in the Hospital: Gaining Perspective and Moving Forward.

Provision of adequate protein is crucial for optimizing outcomes in hospitalized patients. However, the methodologies upon which current recommendations are based have limitations, and little is known about true requirements in any clinical population. In this tutorial, we aim to give clinicians an understanding of how current protein recommendations were developed, an appreciation for the limitations of these recommendations, and an overview of more sophisticated approaches that can be applied to better define protein requirements. A broader perspective of the challenges and opportunities in determining clinical protein requirements can help clinicians think critically about the individualized nutrition care they provide to their patients with the goal of administering adequate protein to optimize outcomes.

Natural Bioactive Food Components for Improving Enteral Tube Feeding Tolerance in Adult Patient Populations.

Tube feeding (TF) is the most common form of nutrition support. In recent years, TF administration has increased among patient populations within and outside hospital settings, in part due to greater insurance coverage, reduced use of parenteral nutrition, and improved formularies suitable for sole source nutrition. With increasing life expectancy and improved access to TFs, the number of adults dependent on enteral nutrition is expected to grow. However, enteral TF intolerance (ETFI) is the most common complication of TFs, typically presenting with at least 1 adverse gastrointestinal event, including nausea, diarrhea, and constipation. ETFI often leads to reductions in TF volume with associated energy and protein deficits. Potentially ensuing malnutrition is a major public health concern due its effects on increased risk of morbidity and mortality, infections, prolonged hospital length of stay, and higher healthcare costs. As such, there is a need for intervention strategies to prevent and reduce ETFI. Incorporating whole foods with bioactive properties is a promising strategy. Emerging research has elucidated bioactive properties of whole foods with specific benefits for the prevention and management of adverse gastrointestinal events commonly associated with TFs. However, lack of evidence-based recommendations and technological challenges have limited the use of such foods in commercial TF formulas. This review addresses research gaps by discussing 5 whole foods (rhubarb, banana, curcumin, peppermint oil, and ginger) with bioactive attributes identified through literature searches and clinical experience as having substantial scientific rationale to consider their application for ETFI in adult populations.

Preoperative Pectoralis Muscle Quantity and Attenuation by Computed Tomography Are Novel and Powerful Predictors of Mortality After Left Ventricular Assist Device Implantation.

BACKGROUND: Skeletal muscle mass decreases in end-stage heart failure and is predictive of clinical outcomes in several disease states. Skeletal muscle attenuation and quantity as quantified on preoperative chest computed tomographic scans may be predictive of mortality after continuous flow (CF) left ventricular assist device (LVAD) implantation. METHODS AND RESULTS: A single-center continuous flow-LVAD database (n=354) was used to identify patients with chest computed tomographies performed in the 3 months before LVAD implantation (n=143). Among patients with computed tomography data available, unilateral pectoralis muscle mass indexed to body surface area and attenuation (approximated by mean Hounsfield units [PHUm]) were measured in each patient with a high intrarater and inter-rater reliability (intraclass correlation coefficients 0.98 and 0.97, respectively). Multivariate Cox regression analyses were performed, censoring at cardiac transplantation, to assess the impact of preoperative pectoralis muscle index and pectoralis muscle mean Hounsfield unit on survival after LVAD implantation. Each unit increase in pectoralis muscle index was associated with a 27% reduction in the hazard of death after LVAD (adjusted hazard ratio, 0.73; 95% confidence interval, 0.58-0.92; P=0.007). Each 5-U increase in pectoralis muscle mean Hounsfield unit was associated with a 22% reduction in the hazard of death after LVAD (adjusted hazard ratio, 0.78; 95% confidence interval, 0.68-0.89; P<0.0001). Pectoralis muscle index and pectoralis muscle mean Hounsfield unit outperformed other traditional measures in the data set, including the HeartMate II risk score. CONCLUSIONS: Pectoralis muscle size and attenuation were powerful predictors of outcomes after LVAD implantation in this data set. This one time, repeatable, internal assessment of patient substrate added valuable prognostic information that was not available on standard preoperative testing.

Long-Term Body Composition Changes in Women Following Roux-en-Y Gastric Bypass Surgery.

BACKGROUND: Although most individuals experience successful weight loss following Roux-en-Y gastric bypass (RYGB), weight regain is a concern, the composition of which is not well documented. Our aim was to evaluate changes in body composition and handgrip strength as a measure of functional status in participants from a previous 1-year post-RYGB longitudinal study who had undergone RYGB approximately 9 years prior. METHODS: Five women from an original larger cohort were monitored pre-RYGB and 1.5 months, 6 months, 1 year, and 9 years post-RYGB. Body composition was assessed at all time points using dual energy x-ray absorptiometry and multiple dilution. Handgrip strength was measured using a digital isokinetic hand dynamometer (Takei Scientific Instruments, Ltd, Tokyo, Japan). RESULTS: Mean time to final follow-up was 8.7 years. Lean soft tissue (LST) loss over the ~9-year period was on average 11.9 ± 5.6 kg. Compared with 1-year post-RYGB, 9-year LST was 4.4 ± 3.0 kg lower ( P = .03). Fat-free mass decreased over the 9-year period by 12.6 ± 5.8 kg. Mean fat mass (FM) decreased from 75.4 ± 22.6 kg pre-RYGB to 35.5 ± 21.5 kg 1 year post-RYGB but then trended toward an increase of 8.6 ± 7.0 kg between 1 year and 9 years post-RYGB ( P = .053). Loss of LST was correlated with loss of handgrip strength ( r = 0.64, P = .0005). CONCLUSION: The continued loss of lean mass associated with decreased handgrip strength occurring with long-term trend toward FM regain post-RYGB is concerning. The loss of LST and functional strength carries particular implications for the aging bariatric population and should be investigated further.

Phase Angle and Impedance Ratio: Reference Cut-Points From the United States National Health and Nutrition Examination Survey 1999-2004 From Bioimpedance Spectroscopy Data.

BACKGROUND: Raw bioimpedance parameters (eg, 50-kHz phase angle [PA] and 200-kHz/5-kHz impedance ratio [IR]) have been investigated as predictors of nutrition status and/or clinical outcomes. However, their validity as prognostic measures depends on the availability of appropriate reference data. Using a large and ethnically diverse data set, we aimed to determine if ethnicity influences these measures and provide expanded bioimpedance reference data for the U.S. METHODS: The National Health and Nutrition Examination Survey (NHANES) is an ongoing compilation of studies conducted by the U.S. Centers for Disease Control and Prevention designed to monitor nutrition status of the U.S. POPULATION: The NHANES data sets analyzed were from the years 1999-2000, 2001-2002, and 2003-2004. RESULTS: Multivariate analysis showed that PA and IR differed by body mass index (BMI), age, sex, and ethnicity (n = 6237; R2 = 41.2%, P < .0001). Suggested reference cut-points for PA stratified by age decade, ethnicity, and sex are provided. CONCLUSION: Ethnicity is an important variable that should be accounted for when determining population reference values for PA and IR. We have provided sex-, ethnicity-, and age decade-specific reference values from PA for use by future studies in U.S. POPULATIONS: Interdevice differences are likely to be important contributors to variability across published population-specific reference data and, where possible, should be evaluated in future research. Ultimately, further validation with physiologically relevant reference measures (eg, dual-energy x-ray absorptiometry) is necessary to determine if PA/IR are appropriate bedside tools for the assessment of nutrition status in a clinical population.

The Use of Technology for Estimating Body CompositionStrengths and Weaknesses of Common Modalities in a Clinical Setting [Formula: see text].

Assessment of body composition, both at single time points and longitudinally, is particularly important in clinical nutrition practice. It provides a means for the clinician to characterize nutrition status at a single time point, aiding in the identification and diagnosis of malnutrition, and to monitor changes over time by providing real-time information on the adequacy of nutrition interventions. Objective body composition measurement tools are available clinically but are often underused in nutrition care, particularly in the United States. This is, in part, due to a number of factors concerning their use in a clinical context: cost and accessibility of equipment, as well as interpretability of the results. This article focuses on the factors influencing interpretation of results in a clinical setting. Body composition assessment, regardless of the method, is inherently limited by its indirect nature. Therefore, an understanding of the strengths and limitations of any method is essential for meaningful interpretation of its results. This review provides an overview of body composition technologies available clinically (computed tomography, dual-energy x-ray absorptiometry, bioimpedance, ultrasound) and discusses the strengths and limitations of each device.

Bioimpedance at the bedside: current applications, limitations, and opportunities.

The loss of muscle mass is a defining characteristic of malnutrition, and there is ongoing interest in the assessment of lean tissue at the bedside. Globally, bioimpedance techniques have been widely appreciated for their noninvasiveness, safety, ease of use, portability, and relatively low cost compared with other clinically available methods. In this brief update, we review the 3 primary types of commercially available bioimpedance devices (single- and multiple-frequency and spectroscopy) and differentiate the underlying theory and current applications of each. We also address limitations and potential opportunities for using these devices at the bedside for clinical assessment. Mixed reports in the validation literature for all bioimpedance approaches have raised questions about absolute accuracy to estimate whole body composition in clinical populations, particularly those with abnormal fluid status and/or body geometry in whom underlying method assumptions may be violated. Careful selection of equations can improve whole body estimates by single- and multiple-frequency techniques; however, not all devices will allow for this approach. Research is increasing on the use of bioimpedance variables including phase angle and impedance ratio as potential markers of nutrition status and/or clinical outcomes; consensus on reference cut-points for interpreting these markers has yet to be established. Novel developments in the bioimpedance spectroscopy approach are allowing for improved fluid management in individuals receiving dialysis; these developments have implications for the clinical management of other conditions associated with fluid overload and may also provide enhanced whole body estimates of lean tissue through new modeling procedures.