Metabolically active component of fat-free body mass: influences of age, adiposity, and gender

Cardiometabolic Risk in Chronic Spinal Cord Injury: A Systematic Review with Meta-Analysis and Temporal and Geographical Trends

Objectives: This systematic review with meta-analysis compared cardiometabolic syndrome (CMS) in adults with chronic (≥1 year) spinal cord injury (SCI) to non-SCI individuals (controls) and athletes, analyzing the effect of specific injury characteristics and exploring temporal and geographical trends. Methods: Ovid Medline, Embase, Cochrane, CINAHL, Scopus, and Web of Science were searched from inception to September 2024. Adults with chronic SCI were included based on observational and baseline data derived from experimental studies. Quality Assessment Criteria for Evaluating Primary Research Papers from a Variety of Fields assessed quality. Weighted means with 95% bootstrapped confidence intervals (CI) were computed for risk stratification. Group differences were assessed using random effects meta-analysis, calculating weighted mean differences with 95% bootstrapped CI. Temporal and geographical trends were evaluated with linear regression based on sample-size-weighted distributions and relevant covariates. Results: Of 31,163 identified records, 471 studies were included (n ≤ 31,782 SCI participants). CMS was present in men with SCI, paraplegia, tetraplegia, and injuries above T6; men with complete SCI (AIS A); and men and women with motor-complete SCI (AIS A-B). Compared to controls, adults with SCI had a lower body mass index (BMI), higher total and visceral fat, and worse lipid and carbohydrate profiles, including increased insulin resistance (IR). Tetraplegia was associated with greater visceral fat, poorer glycemic control, and lower BMI, insulin sensitivity, high-density lipoprotein-cholesterol (HDL-C), and triglycerides than paraplegia. Motor-complete SCI had lower BMI, HDL-C, and fasting glucose than motor-incomplete injuries. Injuries above T6 had lower blood pressure and higher fasting insulin levels than those below T6. Athletes with SCI had a lower BMI, fat mass, and fasting glucose, and higher systolic blood pressure than non-athletes with SCI, but frequently presented with obesity and carbohydrate dysfunction. Temporal analysis revealed increasing obesity trends and improved systolic blood pressure, while other CMS risk factors remained unchanged. We also identified global variations in obesity, lipids, blood pressure, and carbohydrate patterns. Conclusions: With a large sample, we revealed a widespread cardiometabolic burden in chronic SCI, even among athletes. Specifically, obesity, IR, and hypoalphalipoproteinemia worsened with increasing injury severity, alongside rising obesity trends and geographic disparities in risk profiles. These patterns highlight the evolution of what was deemed an epidemic into a global cardiometabolic pandemic.

Pharmacokinetics of ethambutol and weight banded dosing in South African adults newly diagnosed with tuberculosis and HIV

Ethambutol is used to treat tuberculosis (TB) in individuals living with HIV. Low concentrations of ethambutol have been reported in patients dosed with the World Health Organization (WHO)-recommended first-line regimen. We analyzed the pharmacokinetics of ethambutol in 61 HIV-positive individuals diagnosed with drug-sensitive TB enrolled in the tuberculosis and highly active antiretroviral therapy (TB-HAART) study. Participants started on TB treatment and were randomized to early or later introduction of efavirenz-based antiretroviral treatment. We explored potential covariate effects and evaluated the current WHO dosing recommendations for ethambutol in drug-susceptible and multidrug-resistant (MDR)-TB. A two-compartment model with first-order elimination allometrically scaled by fat-free mass and transit compartment absorption best described the pharmacokinetics of ethambutol. Clearance was estimated to be 40.3 L/h for a typical individual with a fat-free mass (FFM) of 42 kg. The Antib-4 formulation had 26% higher bioavailability and slower mean transit time by 37% compared with Rifafour. Simulations showed that individuals in the lower weight bands (<55 kg) who were administered ethambutol at WHO-recommended doses had relatively low drug exposures. These individuals would need doses of 825 mg if their body weight is <37.9 kg and 1,100 mg if it is between 38 and 54.9 kg to achieve the reference maximum concentrations of 2-6 mg/L and an area under the concentration-time curve (0-24) of 16-29 mg·h/L. To achieve these targets in MDR-TB treatment, a dose increment of 400 mg (extra tablet) would be required for individuals in the lower weight band (<46 kg). Our dose adjustments are consistent with the literature and can be recommended for consideration by the WHO for first-line drug-susceptible and MDR-TB treatment.

Energy expenditure of international female rugby union players during a major international tournament: a doubly labelled water study

The purpose of this study was to quantify the total energy expenditure (TEE) of international female rugby union players. Fifteen players were assessed over 14 days throughout an international multi-game tournament, which represented two consecutive one-match microcycles. Resting metabolic rate (RMR) and TEE were assessed by indirect calorimetry and doubly labelled water, respectively. Physical activity level (PAL) was estimated (TEE:RMR). Mean RMR, TEE, and PAL were 6.60 ± 0.93 MJ·day-1 (1578 ± 223 kcal·day-1), 13.51 ± 2.28 MJ·day-1 (3229 ± 545 kcal·day-1), and 2.0 ± 0.3 AU, respectively. There was no difference in TEE (13.74 ± 2.31 (3284 ± 554 kcal·day-1) vs. 13.92 ± 2.10 MJ·day-1 (3327 ± 502 kcal·day-1); p = 0.754), or PAL (2.06 ± 0.26 AU vs. 2.09 ± 0.23 AU; p = 0.735) across microcycles, despite substantial decreases in training load (total distance: -8088 m, collisions: -20 n, training duration: -252 min). After correcting for body composition, there was no difference in TEE (13.80 ± 1.74 (3298 ± 416 adj. kcal·day-1) vs. 13.16 ± 1.97 (3145 ± 471 adj. kcal·day-1) adj. MJ·day-1, p = 0.190), RMR (6.49 ± 0.81 (1551 ± 194 adj. kcal·day-1) vs. 6.73 ± 0.83 (1609 ± 198 adj. kcal·day-1) adj. MJ·day-1, p = 0.633) or PAL (2.15 ± 0.14 vs. 1.87 ± 0.26 AU, p = 0.090) between forwards and backs. For an injured participant (n = 1), TEE reduced by 1.7 MJ·day-1 (-401 kcal·day-1) from pre-injury. For participants with illness (n = 3), TEE was similar to pre-illness (+0.49 MJ·day-1 (+117 kcal·day-1)). The energy requirements of international female rugby players were consistent across one-match microcycles. Forwards and backs had similar adjusted energy requirements. These findings are critical to inform the dietary guidance provided to female rugby players.

Measurement of body composition in postpartum South African women living with and without HIV infection

Background

While several methodologies are available to measure adiposity, few have been validated in sub-Saharan African (SSA) and none in postpartum African women living with HIV (WLHIV). We compared bioelectrical impendence analysis (BIA) and air displacement plethysmography (ADP) against dual x-ray absorptiometry (DXA) in South African women and examined differences by HIV and body mass index (BMI) status.

Methods

Lin's concordance correlation coefficient (CCC) test was used to examine fat mass (FM), fat free mass (FFM), and total body fat percent (%BF) difference between BIA vs. DXA, and ADP vs. DXA in women living with HIV (n = 57) and without HIV (n = 25). The Bland Altman test was used to assess mean differences and the direction of bias.

Results

The median age was 31 years (IQR, 26-35) and months postpartum were 11 (IQR, 7-16), 44% of the women had obesity. Lin's CCC for BIA and ADP vs. DXA were both 0.80 for %BF and 0.97 for FM, and 0.86 and 0.80 for FFM, respectively. Mean differences (DXA-BIA and ADP estimates) were 0.22 ± 4.54% (p = 0.54) and 3.35 ± 3.27% (p < 0.01) for %BF, -0.82 ± 3.56 kg (p = 0.06) and 1.43 ± 2.68 kg (p = 0.01) for FM, -1.38 ± 3.61 kg (p = 0.01) and - 3.34 ± 2.37 kg (p < 0.01) for FFM, respectively. BIA overestimated %BF in WLHIV and underestimated it in women with obesity.

Conclusion

Body composition measurements using BIA and ADP correlated well with DXA, thereby providing alternative, safe tools for measuring postpartum FM and FFM in SSA women, including WLHIV.

Body Cell Mass to Fat-Free Mass Ratio and Extra- to Intracellular Water Ratio Are Related to Maximal Oxygen Uptake

Fat-free mass (FFM) is a heterogeneous compartment comprising body cell mass (BCM), intracellular water (ICW), extracellular solids, and extracellular water (ECW). The BCM/FFM and ECW/ICW ratios vary among individuals and decrease with age. This study aimed to determine whether BCM/FFM and ECW/ICW ratios are predictors of maximal oxygen uptake (V̇̇O2peak) independently of age, sex, and objectively measured physical activity (PA). A total of 115 Japanese males and females, aged 55.3 ± 8.0 years (mean ± standard deviation), were included in the study. Anthropometry, explosive leg muscle power, and V̇̇O2peak were measured, and BCM, FFM, ICW, and ECW were estimated. Step count and PA were objectively measured using a triaxial accelerometer. Blood flow volume was assessed using ultrasonography. BCM and ICW were negatively correlated with age, whereas FFM and ECW were not significantly correlated with age. FFM, ICW/ECW, BCM/FFM, step counts, moderate and vigorous PA, and leg muscle power were positively correlated with V̇̇O2peak, even after adjusting for age and sex (p < .05). Multiple regression analysis indicated that either BCM/FFM or ECW/ICW, leg power, and objectively measured PA were associated with V̇̇O2peak independent of age, sex, and FFM. Blood flow volume was significantly correlated with ECW (p < .05), but not with BCM. The BCM/FFM and ECW/ICW ratios were significant predictors of V̇̇O2peak, independent of age, sex, FFM, leg power, and objectively measured PA.

Relating QRS voltages to left ventricular mass and body composition in elite endurance athletes

PURPOSE

Electrocardiogram (ECG) QRS voltages correlate poorly with left ventricular mass (LVM). Body composition explains some of the QRS voltage variability. The relation between QRS voltages, LVM and body composition in endurance athletes is unknown.

METHODS

Elite endurance athletes from the Pro@Heart trial were evaluated with 12-lead ECG for Cornell and Sokolow-Lyon voltage and product. Cardiac magnetic resonance imaging assessed LVM. Dual energy x-ray absorptiometry assessed fat mass (FM) and lean mass of the trunk and whole body (LBM). The determinants of QRS voltages and LVM were identified by multivariable linear regression. Models combining ECG, demographics, DEXA and exercise capacity to predict LVM were developed.

RESULTS

In 122 athletes (19 years, 71.3% male) LVM was a determinant of the Sokolow-Lyon voltage and product (β = 0.334 and 0.477, p < 0.001) but not of the Cornell criteria. FM of the trunk (β = - 0.186 and - 0.180, p < 0.05) negatively influenced the Cornell voltage and product but not the Sokolow-Lyon criteria. DEXA marginally improved the prediction of LVM by ECG (r = 0.773 vs 0.510, p < 0.001; RMSE = 18.9 ± 13.8 vs 25.5 ± 18.7 g, p > 0.05) with LBM as the strongest predictor (β = 0.664, p < 0.001). DEXA did not improve the prediction of LVM by ECG and demographics combined and LVM was best predicted by including VO₂max (r = 0.845, RMSE = 15.9 ± 11.6 g).

CONCLUSION

LVM correlates poorly with QRS voltages with adipose tissue as a minor determinant in elite endurance athletes. LBM is the strongest single predictor of LVM but only marginally improves LVM prediction beyond ECG variables. In endurance athletes, LVM is best predicted by combining ECG, demographics and VO₂max.

Effect of Exercise on the Resting Metabolic Rate and Substrate Utilization in Women with Gestational Diabetes Mellitus: Results of a Pilot Study

Regular physical activity during pregnancy has a positive effect on the mother and fetus. However, there is scarce data regarding the effect of exercise in pregnancies complicated by gestational diabetes mellitus (GDM). The aim of the present parallel, non-randomized, open-label, pilot, clinical study was to examine the effect of two exercise programs on the resting metabolic rate (RMR) and substrate utilization in pregnancies complicated by GDM, compared with usual care (advice for the performance of exercise). Forty-three pregnant women diagnosed with GDM between the 24th and 28th gestational week, volunteered to participate. Three groups were formed: Usual care (n = 17), Walking (n = 14), and Mixed Exercise (n = 12). The Usual care group was given advice on maintaining habitual daily activities without any additional exercise. The Walking group exercised regularly by walking, in addition to the habitual daily activities. Finally, the Mixed Exercise group participated in a program combining aerobics and strength exercises. Training intensity was monitored continuously using lightweight, wearable monitoring devices. The Walking and Mixed Exercise groups participated in the training programs after being diagnosed with GDM and maintained them until the last week of gestation. RMR and substrate utilization were analyzed using indirect calorimetry for all participants twice: between 27th and 28th gestational week and as close as possible before delivery. No differences were observed between groups regarding body composition, age, and medical or obstetrical parameters before or after the exercise programs. RMR was increased after the completion of the exercise interventions in both the Walking (p = 0.001) and the Mixed Exercise arms (p = 0.002). In contrast, substrate utilization remained indifferent. In conclusion, regular exercise of moderate intensity (either walking, or a combination of aerobic and strength training) increases RMR in women with GDM compared to the lack of systematic exercise. However, based on the present, pilot data, these exercise regimes do not appear to alter resting substrate utilization.

Peak oxygen uptake in sportsmen with spinal cord injury: importance of body composition

BACKGROUND

Although peak oxygen uptake (VO<inf>2peak</inf>) is considered the most useful index of functional capacity, it's difficult to interpret the results of cardiopulmonary exercise testing (CPET) in individuals with spinal cord injury (SCI). In fact, VO<inf>2peak</inf> is usually normalized for total body weight, but body composition in persons with SCI largely varies depending on physical activity and time since injury, with a progressive loss of fat-free mass (FFM). This can lead to a misinterpretation of the cardiopulmonary fitness in this population.

AIM

Our study proposes a methodology of evaluation, based on bioelectrical impedance analysis (BIA), which could provide more individualized and accurate data in sportsmen with SCI.

DESIGN

Case-control study.

POPULATION

Ambulatory patients at the Sports Medicine Unit of the IRCCS A. Gemelli University Polyclinic Foundation, Rome, Italy.

METHODS

Comparison of data derived from BIA, echocardiography and CPET between 10 male sportsmen with complete, high SCI (group T) and 10 able-bodied controls (group C).

RESULTS

Mean VO<inf>2peak</inf>, weight-normalized VO<inf>2peak</inf>, fat-free mass (FFM)-normalized VO<inf>2peak</inf> and body cellular mass (BCM)-normalized values were significantly lower in group T. At the same heart rate (on average the 55% of the maximal theoretical for age), mean of absolute VO<inf>2</inf>, weight-normalized VO<inf>2</inf> and FFM-normalized VO<inf>2</inf> were still significantly lower in group T. Considering the BCM-normalized VO<inf>2</inf>, the group T showed greater values than controls, 39.4±7.8 vs. 31.1±8.5 mL/kg/min.

CONCLUSIONS

Body composition is a crucial factor for properly interpreting a CPET in individuals with SCI. In particular, normalization of VO<inf>2peak</inf> values for the BCM seems the most reliable tool to assess the real functional capacity in this population.

CLINICAL REHABILITATION IMPACT

A more accurate definition of the aerobic power and functional capacity of people with SCI can improve the monitoring of rehabilitations protocols and physical exercise in this population.

Resting energy expenditure in elite athletes: development of new predictive equations based on anthropometric variables and bioelectrical impedance analysis derived phase angle

Background

An accurate estimation of athletes’ energy needs is crucial in diet planning to improve sport performance and to maintain an appropriate body composition. This study aimed to develop and validate in elite athletes new equations for estimating resting energy expenditure (REE) based on anthropometric parameters as well as bioimpedance analysis (BIA)-derived raw variables and to validate the accuracy of selected predictive equations.

Methods

Adult elite athletes aged 18–40 yrs were studied. Anthropometry, indirect calorimetry and BIA were performed in all subjects. The new predictive equations were generated using different regression models. The accuracy of the new equations was assessed at the group level (bias) and at the individual level (precision accuracy), and then compared with the one of five equations used in the general population or three athletes-specific formulas.

Results

One-hundred and twenty-six male athletes (age 26.9 ± 9.1 yrs; weight 71.3 ± 10.9 kg; BMI 22.8 ± 2.7 kg/m²) from different sport specialties were randomly assigned to the calibration (n = 75) or validation group (n = 51). REE was directly correlated with individual characteristics, except for age, and raw BIA variables. Most of the equations from the literature were reasonably accurate at the population level (bias within ±5%). The new equations showed a mean bias −0.3% (Eq. A based on anthropometric parameters) and −0.6% (Eq. B based on BIA-derived raw variables). Precision accuracy (individual predicted-measured differences within ±5%) was ~75% in six out of eight of the selected equations and even higher for Eq. A (82.4%) and Eq. B (92.2%).

Conclusion

In elite athletes, BIA-derived phase angle is a significant predictor of REE. The new equations have a very good prediction accuracy at both group and individual levels. The use of phase angle as predictor of REE requires further research with respect to different sport specialties, training programs and training level.

Dynamic changes in energy expenditure in response to underfeeding: a review

The observation that 64% of English adults are overweight or obese despite a rising prevalence in weight-loss attempts suggests our understanding of energy balance is fundamentally flawed. Weight-loss is induced through a negative energy balance; however, we typically view weight change as a static function, in that energy intake and energy expenditure are independent variables, resulting in a fixed rate of weight-loss assuming a constant energy deficit. Such static modelling provides the basis for the clinical assumption that a 14644 kJ (3500 kcal) deficit translates to a 1 lb weight-loss. However, this '3500 kcal (14644 kJ) rule' is consistently shown to significantly overestimate weight-loss. Static modelling disregards obligatory changes in energy expenditure associated with the loss of metabolically active tissue, i.e. skeletal muscle. Additionally, it disregards the presence of adaptive thermogenesis, the underfeeding-associated fall in resting energy expenditure beyond that caused by loss of fat-free mass. This metabolic manipulation of energy expenditure is observed from the onset of energy restriction to maintain weight at a genetically pre-determined set point. As a result, the observed magnitude of weight-loss is disproportionally less, followed by earlier weight plateau, despite strict compliance to a dietary intervention. By simulating dynamic changes in energy expenditure associated with underfeeding, mathematical modelling may provide a more accurate method of weight-loss prediction. However, accuracy at an individual level is limited due to difficulty estimating energy requirements, physical activity and dietary intake in free-living individuals. In the present paper, we aim to outline the contribution of dynamic changes in energy expenditure to weight-loss resistance and weight plateau.

Effects of adiposity and body composition on adjusted resting energy expenditure in women

OBJECTIVES

Fat-free mass (FFM) accounts for ~80% of the variance in resting energy expenditure (REE), and this relationship is complicated by adiposity. The objective was to compare adjusted REE and contributions of skeletal lean mass and fat mass (FM) to adjusted REE in women with varying adiposity levels using a novel approach.

METHODS

Women were divided into tertiles by body fat percent (%fat): Tertile 1 (T1): %fat = 18.5%-28.4%; Tertile 2 (T2): %fat = 28.5%-33.8%; Tertile 3 (T3): %fat = 34.0%-61.0%. Outcome measures were measured and adjusted REE, body composition (skeletal lean mass, FM, %fat) from dual-energy X-ray absorptiometry, and percent contribution of skeletal lean mass and FM to adjusted REE.

RESULTS

The main effect for tertiles (T1 vs. T2 vs. T3) was significant (p = .001); REE was significantly higher in T3 versus both T1 by 281 kcal/day (p = .001) and T2 by 215 kcal/day (p = .001). Expenditure from skeletal lean mass in T1 was significantly higher than T3 by 3.2% (p = .001). T3 had a significantly higher FM contribution than T1 by 5.1% (p = .001) and T2 by 3.9% (p = .001).

CONCLUSIONS

Women with elevated %fat experienced lower skeletal lean mass contribution and higher FM contribution to adjusted REE. FM may explain more of the variance in REE between women of different levels of adiposity.

Sex influences DNA methylation and gene expression in human skeletal muscle myoblasts and myotubes

Background

Sex differences are known to impact muscle phenotypes, metabolism, and disease risk. Skeletal muscle stem cells (satellite cells) are important for muscle repair and to maintain functional skeletal muscle. Here we studied, for the first time, effects of sex on DNA methylation and gene expression in primary human myoblasts (activated satellite cells) before and after differentiation into myotubes.

Method

We used an array-based approach to analyse genome-wide DNA methylation and gene expression in myoblasts and myotubes from 13 women and 13 men. The results were followed up with a reporter gene assay.

Results

Genome-wide DNA methylation and gene expression differences between the sexes were detected in both myoblasts and myotubes, on the autosomes as well as the X-chromosome, despite lack of exposure to sex hormones and other factors that differ between sexes. Pathway analysis revealed higher expression of oxidative phosphorylation and other metabolic pathways in myoblasts from women compared to men. Oxidative phosphorylation was also enriched among genes with higher expression in myotubes from women. Forty genes in myoblasts and 9 in myotubes had differences in both DNA methylation and gene expression between the sexes, including LAMP2 and SIRT1 in myoblasts and KDM6A in myotubes. Furthermore, increased DNA methylation of LAMP2 promoter had negative effects on reporter gene expression. Five genes (CREB5, RPS4X, SYAP1, XIST, and ZRSR2) showed differential DNA methylation and gene expression between the sexes in both myoblasts and myotubes. Interestingly, differences in DNA methylation and expression between women and men were also found during differentiation (myoblasts versus myotubes), e.g., in genes involved in energy metabolism. Interestingly, more DNA methylation changes occur in women compared to men on autosomes.

Conclusion

All together, we show that epigenetic and transcriptional differences exist in human myoblasts and myotubes as well as during differentiation between women and men. We believe that these intrinsic differences might contribute to sex dependent differences in muscular phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1118-4) contains supplementary material, which is available to authorized users.

Use of the Body Composition Monitor for Fluid Status Measurements in Elderly Malnourished Subjects

Most hemodialysis (HD) patients are able to finish dialysis at or below the normally hydrated weight determined using the body composition monitor (BCM). However, a minority become symptomatic when they are still fluid overloaded based on BCM-measured overhydration (OH). Malnourished patients frequently fall into this group, suggesting that they may have OH that is inaccessible to ultrafiltration. To isolate any effect of malnutrition on BCM-measured OH from those relating to renal failure, OH measurements for 20 elderly subjects with normal renal function who were classified as malnourished were compared with an age-matched cohort with no known nutritional issues. Body composition monitor measurements were also made on five malnourished HD patients. Mean OH for malnourished subjects with normal renal function was not significantly different from an age-matched cohort without known nutritional deficiencies (1.3 and 1.1 L, respectively; p = 0.5). Post-dialysis OH for HD patients ranged from -0.1 to +4.5 L. A slightly elevated BCM-measured OH appears to be common in elderly subjects and may be explained by changes in the composition of adipose tissue. The effect of malnutrition could not be isolated from sarcopenia, but this study supports the need for caution when reducing target weight in vulnerable patients.

Changes in Resting Energy Expenditure in Relation to Body Weight and Composition Following Gastric Restriction: A Systematic Review

In comparison to gastric bypass surgery, gastric restriction without malabsorption more closely simulates dietary adherence while still producing durable weight loss. The latter is achieved despite considerable reductions in resting energy expenditure (REE), and whether REE is adjusted for body weight/composition using ratio- or regression-based methods could influence understanding of how these procedures affect energy balance. This systematic review identified studies that reported REE before and after gastric restriction in order to compare changes using each method. Ratio assessments revealed increases and decreases when REE was expressed per kilogram of body weight and per kilogram of fat-free mass, respectively. In comparison, measured REE tended to be less than predicted from linear regression after surgery. Explanations for these seemingly disparate findings and future directions are discussed.

Body Composition Tools for Assessment of Adult Malnutrition at the Bedside: A Tutorial on Research Considerations and Clinical Applications

Because of the key role played by the body's lean tissue reserves (of which skeletal muscle is a major component) in the response to injury and illness, its maintenance is of central importance to nutrition status. With the recent development of the Academy of Nutrition and Dietetics/American Society for Parenteral and Enteral Nutrition diagnostic framework for malnutrition, the loss of muscle mass has been recognized as one of the defining criteria. Objective methods to evaluate muscle loss in individuals with acute and chronic illness are needed. Bioimpedance and ultrasound techniques are currently the best options for the clinical setting; however, additional research is needed to investigate how best to optimize measurements and minimize error and to establish if these techniques (and which specific approaches) can uniquely contribute to the assessment of malnutrition, beyond more subjective evaluation methods. In this tutorial, key concepts and statistical methods used in the validation of bedside methods to assess lean tissue compartments are discussed. Body composition assessment methods that are most widely available for practice and research in the clinical setting are presented, and clinical cases are used to illustrate how the clinician might use bioimpedance and/or ultrasound as a tool to assess nutrition status at the bedside. Future research needs regarding malnutrition assessment are identified.

The contribution of fat-free mass to resting energy expenditure: implications for weight loss strategies in the treatment of adolescent obesity

Owing to the strong relationship between fat-free mass (FFM) and resting energy expenditure (REE), the preservation of FFM is often emphasized in the treatment of adolescent obesity. Typical treatment regimens including an increased dietary consumption of protein and participation in resistance training are common components of adolescent weight management programs, despite limited evidence of a positive influence of FFM on weight loss outcomes in adolescents. Given the larger volume of FFM in obese relative to normal weight adolescents and the common treatment goals of both maximizing weight loss and attenuating the loss of FFM, a better understanding of the influence of FFM on energy balance is needed to determine whether strategies to preserve lean tissue or maximize absolute weight loss should be most emphasized. We review the associations among FFM, REE, and weight loss outcomes, focusing on how these relationships might influence energy balance in obese adolescents.

Objectively Measured Sleep Patterns in Young Adult Women and the Relationship to Adiposity

Purpose.

The purpose of this study was to examine the relationship between sleep patterns and adiposity in young adult women.

Design.

Cross-sectional.

Setting.

The study took place at two Mountain West region universities and surrounding communities.

Subjects.

Subjects were 330 young adult women (20.2 ± 1.5 years).

Measures.

Sleep and physical activity were monitored for 7 consecutive days and nights using actigraphy. Height and weight were measured directly. Adiposity was assessed using the BOD POD.

Analysis.

Regression analysis, between subjects analysis of variance, and structural equation modeling were used.

Results.

Bivariate regression analysis demonstrated that sleep efficiency was negatively related to adiposity and that the 7-day standard deviations of bedtime, wake time, and sleep duration were positively related to adiposity (p < .05). Controlling for objectively measured physical activity strengthened the relationship between sleep duration and adiposity by 84% but had a statistically negligible impact on all other relationships that were analyzed. However, multivariate structural equation modeling indicated that a model including sleep efficiency, sleep pattern inconsistency (latent variable consisting of the 7-day standard deviations of bedtime, wake time, and sleep duration), and physical activity was the best for predicting percent body fat.

Conclusion.

Inconsistent sleep patterns and poor sleep efficiency are related to adiposity. Consistent sleep patterns that include sufficient sleep may be important in modifying risk of excess body fat in young adult women.

Relative contribution of organs other than brain to resting energy expenditure is consistent among male power athletes

We have previously shown that resting energy expenditure (REE) adjusted by fat-free mass (FFM) in male college athletes remains consistent regardless of FFM. The FFM comprises internal organs with high metabolic activity, such as liver and brain, which account for 60 to 80% of REE in adults. The purpose of the present study is to examine the contribution of internal organs to the REE of the FFM fraction among male power athletes. The study included 37 American male college football players. REE was measured by indirect calorimetry and body composition was measured by dual energy X-ray absorptiometry (DXA). Mass of brain, liver, and kidneys was measured by MRI and mass of heart was estimated by echocardiography. Normal levels of thyroid hormone (triiodothyronine: T3) were confirmed in all subjects prior to the analysis. Multiple regression analysis was used to assess the influence of FFM, fat mass (FM), T3, and mass of organs on variance of REE. Average body weight and FFM were 81.2±11.3 kg and 67.7±7.4 kg, respectively. The relative contributions of liver, kidneys, and heart to REE were consistent regardless of FFM, while the REE of brain was negatively correlated with FFM (r=-0.672, p<0.001). Only FFM and T3 were found to be independent factors influencing REE. These results suggest that a steady contribution of internal organs other than the brain is the major reason for the consistency of the REE/FFM ratio in male power athletes.

The allometry of metabolism and stature: worker fatigue and height in the Tanzanian labor market

If the positive wage-height correlation is at least partially biological in origin, one plausible pathway is the effect of stature on energy expenditure in individuals. If metabolism scales proportionately with stature, then relative to short individuals, taller individuals can produce more energy for a given work task. This also suggests that end-of-the-workday fatigue, or lack of energy, varies inversely with stature. We test this hypothesis with data from the 2004 Tanzanian Household Worker Survey in which workers report the extent of their fatigue at the end-of-the-workday. Ordinal latent variable parameter estimates reveal that relative to short workers, taller workers are less likely to report being tired at the end-of-the-workday. This suggests that the positive wage-height relationship also has a biological foundation whereby the energy requirements and metabolic costs associated with work effort/tasks are inversely related to stature.

BP regulation VI: elevated sympathetic outflow with human aging: hypertensive or homeostatic?

Though conventional wisdom suggests that a rise in blood pressure is a reality of advancing age, in fact, it appears that progressive elevation in sympathetic activity, not necessarily accompanied by increased blood pressure, is intrinsic to cardiovascular aging in humans. The mechanism behind this elevation would seem to reside in homeostatic cardiovascular regulation; nonetheless, the balance of factors that result in elevated sympathetic outflow with age remains elusive. Age-related increases in sympathetic nervous outflow cannot be fully explained by increases in body mass, body adiposity, or other metabolic factors; interrelations among cardiac output, peripheral resistance, and blood pressure may not reflect a determinative hemodynamic interrelation but rather parallel phenomena; and there is no simple linear relationship between baroreflex control and resting levels of sympathetic activity. In contrast to systemic relationships, available data suggest that elevated sympathetic outflow may derive from the inter-relationship between centrally driven sympatho-excitation and a decline in the ability of sympathetic outflow to effect peripheral vascular responses. This review aims to integrate the current knowledge of mechanisms underlying elevated sympathetic outflow with age. It seeks to synthesize these data in the context of proposing that an age-related decline in the ability of sympathetic outflow to effect regional vascular responses incites a compensatory elevation in resting sympathetic activity to maintain homeostatic balance, presumably to maintain adequate control of blood pressure.

Biological mechanisms that promote weight regain following weight loss in obese humans

Weight loss dieting remains the treatment of choice for the vast majority of obese individuals, despite the limited long-term success of behavioral weight loss interventions. The reasons for the near universal unsustainability of behavioral weight loss in [formerly] obese individuals have not been fully elucidated, relegating researchers to making educated guesses about how to improve obesity treatment, as opposed to developing interventions targeting the causes of weight regain. This article discusses research on several factors that may contribute to weight regain following weight loss achieved through behavioral interventions, including adipose cellularity, endocrine function, energy metabolism, neural responsivity, and addiction-like neural mechanisms. All of these mechanisms are engaged prior to weight loss, suggesting that these so called "anti-starvation" mechanisms are activated via reductions in energy intake, rather than depletion of energy stores. Evidence suggests that these mechanisms are not necessarily part of a homeostatic feedback system designed to regulate body weight, or even anti-starvation mechanisms per se. Although they may have evolved to prevent starvation, they appear to be more accurately described as anti-weight loss mechanisms, engaged with caloric restriction irrespective of the adequacy of energy stores. It is hypothesized that these factors may combine to create a biological disposition that fosters the maintenance of an elevated body weight and works to restore the highest sustained body weight, thus precluding the long-term success of behavioral weight loss. It may be necessary to develop interventions that attenuate these biological mechanisms in order to achieve long-term weight reduction in obese individuals.

Effect of constitution on mass of individual organs and their association with metabolic rate in humans--a detailed view on allometric scaling

Resting energy expenditure (REE)-power relationships result from multiple underlying factors including weight and height. In addition, detailed body composition, including fat free mass (FFM) and its components, skeletal muscle mass and internal organs with high metabolic rates (i.e. brain, heart, liver, kidneys), are major determinants of REE. Since the mass of individual organs scales to height as well as to weight (and, thus, to constitution), the variance in these associations may also add to the variance in REE. Here we address body composition (measured by magnetic resonance imaging) and REE (assessed by indirect calorimetry) in a group of 330 healthy volunteers differing with respect to age (17–78 years), sex (61% female) and BMI (15.9–47.8 kg/m²). Using three dimensional data interpolation we found that the inter-individual variance related to scaling of organ mass to height and weight and, thus, the constitution-related variances in either FFM (model 1) or kidneys, muscle, brain and liver (model 2) explained up to 43% of the inter-individual variance in REE. These data are the first evidence that constitution adds to the complexity of REE. Since organs scale differently as weight as well as height the “fit” of organ masses within constitution should be considered as a further trait.

Assessment of analytical methods used to measure changes in body composition in the elderly and recommendations for their use in phase II clinical trials

It is estimated that in the next 20 years, the amount of people greater than 65 years of age will rise from 40 to 70 million, and will account for 19% of the total population. Age-related decreases in muscle mass and function, known as sarcopenia, have been shown to be related to functional limitation, frailty and an increased risk of morbidity and mortality. Therefore, with an increasing elderly population, interventions that can improve muscle mass content and/or function are essential. However, analytical techniques used for measurement of muscle mass in young subjects may not be valid for use in the elderly. Therefore, the purpose of this review is to examine the applied specificity and accuracy of methods that are commonly used for measurement of muscle mass in aged subjects, and, to propose specific recommendations for the use of body composition measures in phase II clinical trials of function-promoting anabolic therapies.

Energy expenditure and aging

The study of energy expenditure (EE) has deep roots in understanding aging and lifespan in all species. In humans, total EE decreases substantially in advanced age resulting from parallel changes in resting metabolic rate (RMR) and activity EE. For RMR, this reduction appears to be due to a reduction in organ mass and specific metabolic rates of individual tissues. However, these anatomical changes explain very little regarding the decline in activity EE, which is governed by both genetic and environmental sources. The biological control centers for activity EE are closely coupled with body mass fluctuations and seem to originate in the brain. Several candidate neuromodulators may be involved in the age-related reduction of activity EE that include: orexin, agouti-related proteins and dopaminergic pathways. Unfortunately, the existing body of research has primarily focused on how neuromodulators influence weight gain and only a few studies have been performed in aging models. Recent evidence suggests that activity EE has an important role in dictating lifespan and thus places emphasis on future research to uncover the underlying biological mechanisms. The study of EE continues to unlock clues to aging.

Body size and human energy requirements: reduced mass-specific resting energy expenditure in tall adults

Two observations favor the presence of a lower mass-specific resting energy expenditure (REE/weight) in taller adult humans: an earlier report of height (H)-related differences in relative body composition; and a combined model based on Quetelet and Kleiber's classic equations suggesting that REE/weight proportional, variantH(-0.5). This study tested the hypothesis stating that mass-specific REE scales negatively to height with a secondary aim exploration of related associations between height, weight (W), surface area (SA), and REE. Two independent data sets (n = 344 and 884) were evaluated, both with REE measured by indirect calorimetry and the smaller of the two including fat estimates by dual-energy X-ray absorptiometry. Results support Quetelet's equation (W proportional, variantH(2)), but Kleiber's equation approached the interspecific mammal form (REE proportional, variantW(0.75)) only after adding adiposity measures to weight and age as REE predictors. REE/weight scaled as H( approximately (-0.5)) in support of the hypothesis with P values ranging from 0.17 to <0.001. REE and SA both scaled as H( approximately 1.5), and REE/SA was nonsignificantly correlated with height in all groups. These observations suggest that adiposity needs to be considered when evaluating the intraspecific scaling of REE to weight; that relative to their weight, taller subjects require a lower energy intake for replacing resting heat losses than shorter subjects; that fasting endurance, approximated as fat mass/REE, increases as H(0.5); and that thermal balance is maintained independent of stature by evident stable associations between resting heat production and capacity of external heat release. These observations have implications for the modeling of adult human energy requirements and associate with anthropological concepts founded on body size.

Laboratory and field measurements of body composition

Objective

This background paper was prepared in response to a request to review the concepts related to measurement of body composition, to discuss laboratory and field methods of assessing body composition and to discuss the practical applications of the methods – how they might be used singly or in combination to provide data for a selected population.

Design

The common laboratory and field methods are described and discussed, with particular attention to the assumptions involved and the applicability of the methods to the different population groups. Most measurements of body composition are made in the field, at the bedside or clinic as opposed to in the laboratory. The laboratory methods have a role to play in their own right, in research into new concepts, models and methods. However, they are particularly important in establishing the accuracy of the field methods.

Setting

Field, bedside and laboratory studies.

Subjects

Children, adults, the elderly, ethnic groups.

Results

Laboratory estimates of body compositions are best performed by multi-component methods or by 2-component methods adjusted for to the populations under investigation. There is a scarcity of data for most of the populations in the world.

Conclusions

Energy requirements based on body weight are an approximation since they do not take into account differences in body composition, which will better determine the true requirements. The measurement of body composition occurs in many branches of biology and medicine. It is used in the assessment of nutritional and growth status and in disease states and their treatment. Energy stores, skeletal muscle and protein content can be determined and changes monitored. In human energetics, body composition is widely used for the standardisation of other variables, such as basal metabolic rate (BMR), in the assessments of ethnic and environmental differences and of variability and adaptation to different levels of nutrition. Choosing a method is very problematic. Users want simple, inexpensive, rapid, safe accurate methods to measure body composition but speed and simplicity come at the expense of accuracy. Recommendations are made for age, sex, and in some cases, fatness and ethnic specific methods.

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

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

Comparison of three methods of nutritional assessment in liver cirrhosis: subjective global assessment, traditional nutritional parameters, and body composition analysis

BACKGROUND

Liver cirrhosis affects the results of many of the traditional techniques currently used to evaluate nutritional status. Our aim was to compare the traditional two-compartment model (subjective global assessment and anthropometry and blood tests) of nutritional assessment with a multicompartmental model (body composition analysis) in patients with cirrhosis.

METHODS

Seventy-nine patients and 17 control subjects were studied. Subjective global assessment, anthropometry and blood tests, and body composition analysis were performed for each. The two most important compartments were body cell mass and total body fat. The subjects were classified by each method as well nourished or moderately or severely malnourished.

RESULTS

Twenty-five patients (31.6%) were malnourished according to the subjective global assessment, 2 (6.3%) with Child's class A cirrhosis, 10 (34.5%) with class B, and 13 (72.2%) with class C, whereas 24 (30.4%) were malnourished according to the traditional model, 5 (15.6%) in the Child's A group, 8 (27.6%) in B, and 11 (61.1%) in C. According to the multicompartmental model, 48 patients (60.1%) were malnourished, 11 (34.4%) in Child's A, 20 (69%) in B, and 17 (94.4%) in C. The use of the multicompartmental model increased the prevalence of malnutrition by more than 60% in Child's classes A and B patients and by more than 20% in Child's class C patients.

CONCLUSIONS

Traditional nutritional assessment, although easier, underestimated the prevalence and severity of malnutrition in patients with cirrhosis. The underestimation was more pronounced in Child's class A and B patients.

Greater than predicted decrease in resting energy expenditure with age: cross-sectional and longitudinal evidence

OBJECTIVE

To determine whether the age-related decrease in resting energy expenditure (REE) is explained by variations in body composition.

DESIGN

In Study 1, adult subjects (20-70 years) from the Quebec Family Study were classified into five different age groups. Body composition was measured by hydrodensitometry to determine fat mass and fat-free mass as predictors of REE. In the youngest group of individuals these predictors were used to plot a reference regression that was then used to predict REE in the other age groups. In Study 2, this issue was investigated in a longitudinal design (6-year follow-up). Subjects were subdivided into three groups and a reference regression was plotted at the beginning of the follow-up and was then used to predict REE 6 years later in the three age groups.

SUBJECTS

In Study 1, 627 adults (288 men and 339 women), aged between 20 and 70 years. In Study 2, 191 adults (93 men and 98 women).

RESULTS

In Study 1, measured REE was 329, 302, 528 and 636 kJ/day (P < 0.0001) below predicted REE at 34, 44, 54 and 64 years, respectively. In Study 2 the most marked deviation from predicted REE in response to the 6-year follow-up in men was observed in young adults (-548 kJ/day, P < 0.001) while in women, the largest deviation occurred later in life (-720 kj/day, P < 0.001).

CONCLUSION

Aging is accompanied by a decrease in REE that is significantly greater than what is predicted by variations in body composition. This decrease may reach a mean level of about 500-800 kj/day.

Glucose in parenteral nutrition: a survey of U.S. medical centers

BACKGROUND

A previous report suggested that glucose administration in total parenteral nutrition (TPN) should not exceed 4 mg/kg/min with a respiratory quotient (RQ) >1.0. This rate would not be exceeded, in most patients, with a TPN glucose concentration of 15%. Our previous survey of hospitals, 7 years ago, of TPN composition revealed use of excessive glucose. Our purpose was to reevaluate glucose usage in TPN.

METHODS

A subset of data from 45 hospitals participating in Novation's Medication Use Evaluation program, "Parenteral Nutrition for Adults and Neonates" study, was analyzed to document glucose administration in TPN.

RESULTS

Data of 629 adult patients from 44 hospitals receiving TPN were analyzed. Of these, 30 hospitals with 478 patients had 100 patients (15.9% of the total) with TPN glucose infusion rates >4 mg/kg/min, whereas 27 hospitals, or 61%, had average TPN glucose concentrations above 15%. This could be associated with an RQ >1.0, implying increased net lipogenesis.

CONCLUSIONS

The majority of hospitals surveyed were found, as in a previous survey, to be using amounts of glucose in TPN which would be expected to be associated with an RQ >1.0, implying increased net lipogenesis.

A cellular-level approach to predicting resting energy expenditure across the adult years

BACKGROUND

We previously derived a whole-body resting energy expenditure (REE) prediction model by using organ and tissue mass measured by magnetic resonance imaging combined with assumed stable, specific resting metabolic rates of individual organs and tissues. Although the model predicted REE well in young persons, it overpredicted REE by approximately 11% in elderly adults. This overprediction may occur because of a decline in the fraction of organs and tissues as cell mass with aging.

OBJECTIVE

The aim of the present study was to develop a cellular-level REE prediction model that would be applicable across the adult age span. Specifically, we tested the hypothesis that REE can be predicted from a combination of organ and tissue mass, the specific resting metabolic rates of individual organs and tissues, and the cellular fraction of fat-free mass.

DESIGN

Fifty-four healthy subjects aged 23-88 y had REE, organ and tissue mass, body cell mass, and fat-free mass measured by indirect calorimetry, magnetic resonance imaging, whole-body (40)K counting, and dual-energy X-ray absoptiometry, respectively.

RESULTS

REE predicted by the cellular-level model was highly correlated with measured REE (r = 0.92, P < 0.001). The mean difference between measured REE (x+/- SD: 1487 +/- 294 kcal/d) and predicted REE (1501 +/- 300 kcal/d) for the whole group was not significant, and the difference between predicted and measured REE was not associated with age (r = 0.009, NS).

CONCLUSION

The present approach establishes an REE-body composition link with the use of a model at the cellular level. The combination of 2 aging-related factors (ie, decline in both the mass and the cellular fraction of organs and tissues) may account for the lower REE observed in elderly adults.

Potassium per kilogram fat-free mass and total body potassium: predictions from sex, age, and anthropometry

Total body potassium (TBK) is located mainly intracellularly and constitutes an index of fat-free mass (FFM). The aim was to examine whether TBK and the TBK-to-FFM ratio (TBK/FFM) can be estimated from sex, age, weight, and height. A primary study group (164 males, 205 females) and a validation group (161 and 206), aged 37-61 yr, were randomly selected from the general population. TBK was determined by whole body counting, and FFM was obtained by dual-energy X-ray absorptiometry (DEXA; FFM(DEXA)). The primary study group was used to construct sex-specific equations predicting TBK and TBK/FFM from age, weight, and height. The equations were used to estimate TBK and TBK/FFM in the validation group. The estimates were compared with measured values. TBK in different age ranges was predicted, with errors ranging from 5.0 to 6.8%; errors for TBK/FFM ranged from 2.7 to 4.8%, respectively. By adding FFM(DEXA) as a fourth predictor, the error of the TBK prediction decreased by approximately two percentage units. In conclusion, TBK and TBK/FFM can be meaningfully estimated from sex, age, weight, and height.

A theory for normalizing resting .VO(2) for differences in body size

PURPOSE

The purpose of this paper was two-fold: 1) to present a method of normalizing data for differences in body size that is consistent with the dimensional relationship between mass and power, and can be universally applied to subjects of any age, sex, or size without statistical cross-validation; and 2) to apply the model to data gathered from boys, girls, men, and women to determine whether or not age- and sex-dependent differences in resting .VO(2) exist.

METHODS

Mass, percent body fat, and resting .VO(2) were measured in 39 boys, 40 girls, 40 men, and 40 women.

RESULTS

Dimensional analysis predicted .VO(2) = a fat-free mass (FFM)2/3, with a defined as the size-independent metabolism of FFM. Bivariate correlation revealed the association between .VO(2) and FFM in children was consistent with biological similarity but not in men and women. Group mean .VO(2).FFM(-2/3) (mL.min(-1).kg(-2/3)) was significantly greater in children (21.7 +/- 2.62) than adults (16.7 +/- 2.30). Also, .VO(2).FFM(-2/3) of female subjects was significantly lower than male subjects in children (girls: 21.0 +/- 2.46; boys: 22.5 +/- 2.61) and adults (women: 15.0 +/- 2.39; men: 16.5 +/- 2.21).

CONCLUSIONS

The dimensional paradigm indicated that mass exponents not equal to 2/3 simultaneously factor out size-dependent and size-independent differences that accompany differences in size. Therefore, size-independent comparisons can only be made using the theoretical mass exponent of 2/3. Also, the experimental results indicated that structural changes accompanying growth must be different from those hypothesized to be the cause of 3/4 scaling in adult animals of different size and species.

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

OBJECTIVE

To validate bio-electric impedance spectroscopy (BIS) by comparison with other methods for determination of body water compartments in stable subjects with an ileostomy and no or minor small bowel resection for inflammatory bowel disease (IBD).

SUBJECTS

Twenty-one subjects were included, age range 36-65 y (female/male=12/9), Crohn's disease (CD), n=14, ulcerative colitis (UC), n=6 and indeterminate colitis (IDC), n=1.

METHODS

Fluid compartments were assessed by the use of three independent methods: BIS, dual-energy X-ray absorptiometry (DXA) and dilution techniques (DIL); tritiated water (total body water, TBW); and bromide (extracellular water, ECW), respectively. Intra-cellular water (ICW) was calculated as TBW-ECW. For comparison TBW was also predicted according to an empirical formula. Differences were analysed using Bland-Altman plots.

RESULTS

The mean TBW values obtained from the impedance measurement differed in the order of -2.21 (DIL) to 1.41 (DXA) in women and -2.01 (DIL) to 2.61 (DXA) in men, from the measured and derived values of total body water. Prediction of TBW gave values that were close to BIS, with a mean difference of -0.31 in male subjects and +0.51 in female subjects. Assessment of ECW revealed that the mean difference between dilution and impedance was less in women than in men (P<0.01).

CONCLUSION

The differences between all methods to assess fluid compartments are pronounced. To further investigate the use of the method in clinical practice for dynamic monitoring of rehydration in ileostomates with acute diarrhoea, repeated measurements together with comparison with weight fluid-balance charts are suggested.

SPONSORSHIP

The study was supported by grants from the Swedish Medical Research Council (17X-03117), Göteborgs Läkarsällskap and IB and A Lundbergs forskningsstiftelse.

Evaluation of different methods for assessing intracellular fluid in healthy older people: a cross-validation study

OBJECTIVES

To cross-validate existing anthropometric and bioimpedance equations to establish their validity and accuracy for estimating intracellular water (ICW) in healthy older Germans and to develop a new equation with improved accuracy and precision for predicting ICW from multifrequency bioimpedance analysis (MFBIA).

DESIGN

Cross-validation study.

SETTING

University of Mainz.

PARTICIPANTS

One hundred fifty-five healthy volunteers aged 60 to 80 years (77 men, 78 women; mean ages +/- standard deviation 67.7 +/- 4.8 and 68.6 +/- 5.5 years, respectively).

MEASUREMENTS

ICW was measured by whole-body counting of (40)potassium ((40)K) ((40)K method) as the reference method and compared by cross-validation techniques against five existing bioimpedance and three anthropometric prediction equations. A new equation for estimating ICW from MFBIA was developed using the (40)K method as criterion method.

RESULTS

Compared with the (40)K method, the existing bioimpedance and anthropometric equations showed large prediction errors in ICW estimates for older men (-32.3% to +37.7%) and women (-34.2% to +26.6%), depending significantly and positively on ICW volume and inversely on weight. A new equation for estimating ICW from MFBIA was developed (R(2)=0.933, standard error of the estimate (SEE)=0.92 L) involving phase angle at 5 kHz, impedance, height, and gender, with data from 100 subjects chosen at random. Cross-validation on an independent group (n=55, R(2)=0.958, SEE=0.68 L) showed no significant bias (0.013 +/- 1.52 L).

CONCLUSIONS

Published bioimpedance and anthropometric prediction equations are not applicable to older Germans because they might be population-specific. The bioimpedance equation of the manufacturer of the bioimpedance analyzer used in this study provides accurate estimates of ICW for normal weight, but not overweight, older men. The newly developed equation improves accuracy and precision of ICW estimates by MFBIA.

Is resting metabolic rate different between men and women?

A low resting metabolic rate (RMR) has been proposed as a possible cause for the increased body fat commonly seen in women compared with men. Absolute RMR is higher in men, but whether RMR adjusted for lean body mass (LBM) remains higher is unresolved. The objective of the present study was to determine whether RMR adjusted for various body composition factors differed between healthy adult men and women. Thirty men years, BMI and twenty-eight women years, BMI were included in the analyses. RMR was measured by open-circuit indirect calorimetry for 60 min. Extracellular water (ECW) was measured by corrected Br(-) space and total body water (TBW) by 2H dilution. LBM was estimated as TBW/0.732. Intracellular water (ICW) was calculated as TBW-ECW, and body cell mass (BCM) as ICW/0.732. Men were heavier and had higher BMI, LBM, BCM and ECW, but less fat mass. Absolute RMR was higher in men than women v. P<0.0001). This difference became non-significant when RMR was adjusted for LBM by ANCOVA v. P=0.2191), but remained significant when adjusted for BCM v. P=0.0249). Fat mass explained a significant amount of variation in RMR in women (r(2) 0.28, P=0.0038), but not in men (r(2) 0.03, P=0.3301). The relationships between body fat and the various subcompartments of BCM and RMR require further elucidation.

New equations for estimating body cell mass from bioimpedance parallel models in healthy older Germans

The objectives of this study were to assess for elderly Germans the validity of existing equations for predicting body cell mass (BCM) and to develop from single- and multifrequency bioimpedance (SFBIA, MFBIA) models new prediction equations. In a data-splitting approach, validation and cross-validation were performed in 160 healthy elderly (60- to 90-yr) subjects. BCM was determined using a tetrapolar bioimpedance analyzer (800 microA; 4 fixed frequencies: 1, 5, 50, and 100 kHz; electrodes placed to hand, wrist, ankle, and foot) and whole body (40)K counting as a reference method. New prediction equations were derived by multiple stepwise regression analysis. The Bland-Altman procedure was used for methods comparison. Relative to whole body counting, the manufacturer's equation overestimated BCM by 9% in men (P < 0.0001, paired t-test) and 4% in women (P = 0.002). Compared with the manufacturer's equation, the newly derived equations (r = 0.92, RMSE = 6-9%) improved accuracy (pure error = 13 vs. 7-8%) and reduced bias and limits of agreement. SFBIA and MFBIA equations did not differ in precision or accuracy. We conclude that the newly derived equations improved BCM estimates in the elderly compared with existing equations. There was no advantage of MFBIA over SFBIA equations.

Age-related differences in fat-free mass, skeletal muscle, body cell mass and fat mass between 18 and 94 years

OBJECTIVE

To determine (1) lean and fat body compartments, reflected by fat-free mass (FFM), appendicular skeletal muscle mass (ASMM), body cell mass (BCM), total body potassium (TBK), fat mass and percentage fat mass, and their differences between age groups in healthy, physically active subjects from 18 to 94 y of age; and (2) if the rate of decrease in any one of the parameters by age might be accelerated compared to others.

METHODS

A total of 433 healthy ambulatory Caucasians (253 men and 180 women) aged 18--94 y were measured by dual-energy X-ray absorptiometry (DXA) and whole body scintillation counter (TBK counter) using a large sodium iodide crystal (203 mm diameter).

RESULTS

The ASMM change (-16.4 and -12.3% in men and women, respectively) in >75 y-old compared to 18 to 34-y-old subjects was greater than the FFM change (-11.8 and -9.7% in men and women, respectively) and this suggests that skeletal muscle mass decrease in older subjects was proportionally greater than non-skeletal muscle mass. BCM (-25.1 and -23.2% in men and women, respectively) and TBK differences were greater than the differences in FFM or ASMM suggesting altered composition of FFM in older subjects. Women had lower peak FFM, ASMM, BCM and TBK than men.

CONCLUSIONS

The decline in FFM, ASMM, BCM and TBK is accelerated in men and women after 60 y of age and FFM, ASMM, BCM and TBK are significantly lower than in younger subjects. Fat mass continued to increase until around 75 y.

Prediction of basal metabolism from organ size in the rat: relationship to strain, feeding, age, and obesity

Use of the weight of various organs and tissues together with their specific metabolic activity for prediction of basal metabolism (BM) seems to be promising. In this study we compared the use of this method with those based on simple or multiple regression analyses. We observed that 97.4% of differences in BM in a group of nine adult male Wistar rats weighing 273–517 g could be accounted for by changes in tissue and organ weights. BM measured in lean Zucker and Sprague-Dawley rats did not diverge from the prediction of the model by >1.6%. According to the organ-based model as well as multiple regression analyses, but not simple regression analyses, BM was increased 18–21% in young rats, decreased 6–7% in food restricted/refed rats, and decreased 19–21% in aged rats. Only with obese rats did the predictions of the two methods diverge. The main reason for this discrepancy seems to be the way adipose tissue size and metabolism are taken into account.

Age-related decline in body cell mass in elderly men and women, determined by a noninvasive nuclear technique: effects of physical activity and dietary potassium intake

The body cell mass (BCM) represents the actively metabolizing cellular components of the human body. In this study, the hypothesis was tested that physical activity and a sufficient dietary intake of potassium attenuate the age-related decline in BCM in the elderly. Cross-sectional data were collected in 82 male and 79 female non-institutionalized elderly (60-90 years) from Mainz, Germany, and were analyzed by age groups. BCM was calculated from total body potassium, measured by whole-body counting of naturally occurring 40K. Physical activity level (PAL) was assessed by a standardized questionnaire. Dietary intake of potassium (DIP) was estimated from a 7-day food diary. The results showed the following trends: (1) BCM decreased continuously from age 60 to 90 years by 11.2% (men) and 7.0% (women). BCM was inversely correlated with age in both sexes (men, P < 0.001; women, P < 0.05), but significant age group differences only existed for men (P < 0.01, one-way analysis-of-variance). Women had less BCM than men in all age groups (P < 0.001, t tests). (2) Correlation analyses demonstrated that in both sexes PAL declined with advancing age (P < 0.05), whereas DIP did not change significantly with age. (3) In both sexes, BCM showed a strong positive correlation with PAL (P < 0.001), but did not correlate significantly with DIP. Multiple linear regression analysis (independent variables were PAL, DIP, age, height, weight) demonstrated that PAL, age, and height explained 45% of the variability in BCM in men. In women, PAL was the only significant predictor of BCM, explaining 23% of the variance. The study supports the hypothesis that the level of physical activity is associated with the decline of BCM in the elderly.

Overnutrition and undernutrition as modifiers of metabolic processes in disease states

Both overnutrition and undernutrition affect energy metabolism, with overnutrition raising energy expenditure and undernutrition lowering it. Fever is a powerful stimulator of thermogenesis. In diseases such as cancer, AIDS, diabetes mellitus, and rheumatoid arthritis, whether energy expenditure is increased or decreased often depends on how advanced the disorder is. Early on, when the greater protein turnover characteristic of these conditions is paramount, energy expenditure is increased. In addition, in diseases such as cancer, AIDS, and rheumatoid arthritis in which cytokines are released, the cytokines' thermogenic effect initially increases the metabolic rate. However, as the disease becomes more advanced and leads to cachexia, energy expenditure drops below normal. Acute conditions such as burns and trauma significantly raise energy expenditure, primarily by increasing sympathetic response and the release of catecholamines, which are powerful stimulators of energy expenditure.

Electronic parenteral and enteral nutrition

BACKGROUND

With reports of deleterious effects of total parenteral nutrition (TPN) in adults in addition to our surveys, which indicated that 1/4, and as many as 1/2, of US academic medical centers were using excess glucose in TPN, our objective was to devise a computer program to optimize nutrients in parenteral and enteral nutrition in adult and pediatric patients.

METHODS

From review of the literature, body composition, including total body water and body cell mass (BCM), were calculated from large published databases. A computer program, based on a previous algorithm, was developed to determine optimum parenteral and enteral nutritional support, based on calculated BCM as the reference. Flexibility to permit any nutrients, in accordance with individual patient requirements, was included.

RESULTS

With entry of simple anthropometric values and an average stress factor equivalent to 20% greater than the Harris-Benedict energy calculation, energy and nutrients were calculated for TPN as follows: amino acids, 3.4 g/kg BCM/d; carbohydrate, 12 g/kg BCM/d; and fat for remaining energy, usually 2.3 g/kg BCM/d. The program, available on any personal computer, is available using Netscape 3.0 or higher or from Microsoft Internet Explorer 4.0, at http://epen.kumc.edu. It permits rapid calculation and display of body composition values, a standardized TPN formula, an alternate TPN prescription, enteral nutrition options, a section that explains the calculations, and a list of references.

CONCLUSIONS

The program, http://epen.kumc.edu, provides rapid definition of the TPN or enteral prescription for adult and pediatric patients, with reduced likelihood of providing excessive glucose and energy in parenteral or enteral nutrition.

The relationship between body composition and physical performance in older women

BACKGROUND

The relationship between age-associated change in body composition and physical disability is still unknown. Skeletal muscle mass declines with age in both sexes; however, since women have less muscle mass per unit of weight than men, these changes may be more debilitating in women.

OBJECTIVE

To evaluate the relationship between body composition and physical performance.

DESIGN

A cross-sectional study.

PARTICIPANTS

144 women aged 68 to 75 were selected randomly from the general population of Verona.

MEASUREMENTS

Body composition was evaluated using dual energy X-ray absorptiometry and bioimpedance. Physical performance was evaluated using a modified version of the Activities of Daily Living scale. Distance walked in 6 minutes was calculated, and isometric knee strength was tested.

RESULTS

Normal women had a significantly lower body mass index (BMI) and percent body fat. These women also had a higher ratio of body cell mass (BCM) and total fat free mass (FFM) than women with physical impairments. After adjusting for BMI, women in the lowest tertile of muscle strength had significantly lower BCM than those in the highest tertile.

CONCLUSIONS

These cross-sectional data show that although muscle strength is related to fat-free mass, disability in older women is associated with heavier BMI and with a higher percentage of body fat.