Advances in the understanding of specific metabolic rates of major organs and tissues in humans.

Purpose Of Review: To present recent evidence on organ and tissue metabolic rates in humans to explain the variance in resting energy expenditure (REE).

Recent Findings: In humans, present knowledge on specific metabolic activities (i.e.

Estimation of total body skeletal muscle mass in Chinese adults: prediction model by dual-energy X-ray absorptiometry.

Background: There are few reports on total body skeletal muscle mass (SM) in Chinese. The objective of this study is to establish a prediction model of SM for Chinese adults.

Methodology: Appendicular lean soft tissue (ALST) was measured by dual energy X-ray absorptiometry (DXA) and SM by magnetic resonance image (MRI) in 66 Chinese adults (52 men and 14 women).

New insights into scaling of fat-free mass to height across children and adults.

Objective: Forbes expressed fat-free mass (FFM, in kg) as the cube of height (H, in m): FFM = 10.3 × H(3). Our objective is to examine the potential influence of gender and population ancestry on the association between FFM and height.

High ratio of resting energy expenditure to body mass in childhood and adolescence: a mechanistic model.

Background: Children have lower resting energy expenditure (REE) but higher ratio of resting energy expenditure to body mass (REE/BM) than do adults. This well-known observation has never been quantitatively explained.

Objectives: The aim of the present study is to understand the high REE/BM in childhood and adolescence.

Evaluation of specific metabolic rates of major organs and tissues: comparison between nonobese and obese women.

Elia (1992) identified the specific resting metabolic rates (K(i)) of major organs and tissues in young adults with normal weight: 200 for liver, 240 for brain, 440 for heart and kidneys, 13 for skeletal muscle, 4.5 for adipose tissue and 12 for residual mass (all units in kcal/kg per day). The aim of the present study was to assess the applicability of Elia's K(i) values for obese adults.

Evaluation of specific metabolic rates of major organs and tissues: comparison between men and women.

Objectives: The specific resting metabolic rates (K(i) , in kcal/kg per day) of major organs and tissues in the Reference Man were suggested in 1992 by Elia: 200 for liver, 240 for brain, 440 for heart and kidneys, 13 for skeletal muscle, 4.5 for adipose tissue and 12 for the residual mass. However, it is unknown whether gender influences the K(i) values.

Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure.

Background: The specific resting metabolic rates (K(i); in kcal · kg(-1 )· d(-1)) of major organs and tissues in adults were suggested by Elia (in Energy metabolism: tissue determinants and cellular corollaries. New York, NY: Raven Press, 1992) to be as follows: 200 for liver, 240 for brain, 440 for heart and kidneys, 13 for skeletal muscle, 4.5 for adipose tissue, and 12 for residual organs and tissues.

Total body carbon and oxygen masses: evaluation of dual-energy x-ray absorptiometry estimation by in vivo neutron activation analysis.

Oxygen and carbon are the first and second abundant elements, respectively, in the human body by mass. Although many physiological and pathological processes are accompanied with alteration of total body oxygen (TBO) and carbon (TBC) masses, in vivo measurements of the two elements are limited. Up to now, almost all available information of TBC and TBO is based on in vivo neutron activation (IVNA) analysis which is very expensive and involves moderate radiation exposure.

Estimation of percentage body fat by dual-energy x-ray absorptiometry: evaluation by in vivo human elemental composition.

Dual-energy x-ray absorptiometry (DXA) is widely applied for estimating body fat. The percentage of body mass as fat (%fat) is predicted from a DXA-estimated R(ST) value defined as the ratio of soft tissue attenuation at two photon energies (e.g.

A cellular level approach to predicting resting energy expenditure: Evaluation of applicability in adolescents.

We previously derived a cellular level approach for a whole-body resting energy expenditure (REE) prediction model by using organ and tissue mass measured by magnetic resonance imaging (MRI) combined with their individual cellularity and assumed stable-specific resting metabolic rates. Although this approach predicts REE well in both young and elderly adults, there were no studies in adolescents that specifically evaluated REE in relation to organ-tissue mass. It is unclear whether the approach can be applied to rapidly growing adolescents.

Ethnicity-related skeletal muscle differences across the lifespan.

Despite research and clinical significance, limited information is available on the relations between skeletal muscle (SM) and age in adults, specifically among Hispanics, African Americans (AA), and Asians. The aim was to investigate possible sex and ethnic SM differences in adults over an age range of 60 years. Subjects were 468 male and 1280 female adults (> or =18 years).

Evaluation of between-methods agreement of extracellular water measurements in adults and children.

Background: Extracellular water (ECW), a relevant molecular level component for clinical assessment, is commonly obtained by 2 methods that rely on assumptions that may not be possible to test at the time the measurements are made.

Objective: The aim of the current study was to evaluate the degree of agreement between ECW assessment by the sodium bromide dilution (ECW(NaBr)) and total body potassium (TBK; whole-body (40)K counting) to total body water (TBW; isotope dilution) methods (ECW(TBK-TBW)) in an ethnically mixed group of children and adults.

Design: ECW was measured with the ECW(NaBr) and ECW(TBK-TBW) methods in 526 white and African American males and females (86 nonobese children, 193 nonobese adults, and 247 obese adults).

Dual-energy X-ray absorptiometry is a valid tool for assessing skeletal muscle mass in older women.

Assessing skeletal muscle mass (SMM) is critical in studying and detecting sarcopenia. Direct measurements by MRI or computerized tomography are expensive or high in radiation exposure. Dual-energy X-ray absorptiometry (DXA) is promising for body composition assessments, but the validity of DXA for predicting SMM in the elderly is still under investigation.

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

A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TBK); mmol] measured by whole body (40)K counting (WBC) was developed (SM = 0.0082.TBK) and validated in adults in a previous study.

Extracellular water across the adult lifespan: reference values for adults.

Extracellular water (ECW) is a large and clinically important body compartment that varies widely in volume both in health and disease. Interpretation of ECW measurements in the clinical setting requires consideration of potential influencing factors such as age, race, sex and other variables that influence fluid status. An important gap in physiological research is a lack of normative ECW values against which to reference perturbations in fluid homeostasis.

Total-body skeletal muscle mass: estimation by dual-energy X-ray absorptiometry in children and adolescents.

Background: Skeletal muscle (SM) is an important compartment but is difficult to quantify in children and adolescents.

Objective: We investigated the potential of dual-energy X-ray absorptiometry (DXA) for measuring total-body SM in pediatric subjects.

Design: A previously published adult DXA SM prediction formula was evaluated in children and adolescents aged 5-17 y (n = 99) who varied in pubertal maturation stage.

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.

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

Protein is an important body component for monitoring growth, development, and nutritional status. We previously developed a total body potassium (TBK, in mmol) and bone mineral (Mo, in kg) model for predicting total body protein (TBPro, in kg) in adults (TBPro = 0.00252 x TBK + 0.

The end of body composition methodology research?

Purpose Of Review: Over one century of research has led to methods for measuring all major body components at the atomic, molecular, cellular, and tissue-system levels. These remarkable developments have fueled a rapid and sustained increase in 'body composition' biological findings and related publications. Other than small, incremental improvements in available methods, is there no longer a need for developing new body composition methods? This review examines the question: are we approaching the 'end' of body composition methodology research?

Recent Findings: Emerging and rapidly growing areas outside of 'traditional' body composition research are highlighting the need for new and innovative method development.

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.

Comparison of visceral adipose tissue mass in adult African Americans and whites.

Objective: Previous studies have reported racial differences in the amount of visceral adipose tissue (VAT), a risk factor for metabolic diseases. These results are equivocal and have not controlled for hormonal influences on VAT mass. This study was designed to measure the extent to which race is associated with VAT, controlling for total adipose tissue (TAT) mass and testosterone.

Four-compartment cellular level body composition model: comparison of two approaches.

Objective: The aim of this study was to develop and compare two DXA-based four-compartment [body weight=body cell mass (BCM)+extracellular fluid (ECF)+extracellular solids (ECS)+fat] cellular level models.

Research Methods And Procedures: Total body potassium (TBK) model: BCM from TBK by whole-body counting-ECF(TBK)=LST-[BCM(TBK)+0.73 x osseous mineral (Mo)].

Extracellular water: greater expansion with age in African Americans.

Aging is associated with the onset of chronic diseases that lead to pathological expansion of the extracellular water (ECW) compartment. Healthy aging, in the absence of disease, is also reportedly accompanied by a relative expansion of the ECW compartment, although the studies on which this observation is based are few in number, applied different ECW measurement methods, included small ethnically homogeneous subject samples, and failed to adjust ECW for non-age-related influencing factors. The aim of the current study was to examine, in a large (n = 1,538) ethnically diverse [African American (AA), Asian, Caucasian, Hispanic] subject group the cross-sectional relationships between ECW and age after controlling first for other potential factors that may influence fluid distribution.

Race-ethnicity-specific waist circumference cutoffs for identifying cardiovascular disease risk factors.

Background: Waist circumferences (WCs) in white men and women that represent a risk of cardiovascular disease (CVD) equivalent to that of body mass indexes (BMIs; in kg/m2) of 25 and 30 have been identified. However, WC cutoffs for other race-ethnicity groups remain unknown.

Objective: The objective was to determine WC cutoffs for CVD risk in non-Hispanic blacks (blacks), Mexican Americans (MA), and non-Hispanic whites (whites).

Dual-energy x-ray absorptiometry-measured lean soft tissue mass: differing relation to body cell mass across the adult life span.

Lean soft tissue (LST) measured by dual-energy X-ray absorptiometry (DEXA) is used as a metabolic measure in aging research despite evidence of extracellular fluid expansion and a corresponding reduction in body cell mass (BCM) in older participants. We investigated the hypothesis that the fraction of LST as BCM is smaller with greater age. Men and women (n = 2043) had DEXA and 40K-counting for body potassium and BCM measured on the same day.