DXA: Potential for Creating a Metabolic Map of Organ‐Tissue Resting Energy Expenditure Components

Abstract

Res. 2002;10:969 -977. Objective: This study tested the hypothesis that tissue-organ components can be derived from DXA measurements, and in turn, resting energy expenditure (REE) can be calculated from the summed heat productions of DXA-estimated brain, skeletal muscle mass (SM), adipose tissue, bone, and residual mass (RM). Research Methods and Procedures: Subjects were divided into five groups of adults Ͻ50 years of age. The specific metabolic rate of RM was developed in 13 Group I healthy subjects and a DXA-brain mass prediction formula in 52 Group II subjects. SM, adipose tissue, and bone models were developed based on earlier reports. The composite REE prediction model (REEp) was tested in 154 Group III subjects in whom REEp was compared with measured REE (REEm). Features of the developed model were determined in 94 normal-weight men and women (Group IV) and seven spinal cord injury patients and healthy matched controls (Group V). New insights into the sources and distribution of REE were provided by analysis of the demonstration groups. Discussion: This approach offers a new practical and educational opportunity to examine REE in subject groups using modeling strategies that reveal the magnitude and distribution of fundamental somatic heat-producing units.

Differences between brain mass and body weight scaling to height: potential mechanism of reduced mass-specific resting energy expenditure of taller adults

“…Compartment volumes were converted to mass using previously reported (7,37) densities for adipose tissue (0.92 kg/l), SM (1.04 kg/l), and ATFM (1.04 kg/l). Bone mineral content (BMC) was measured by DXA on the same day and results were converted to bone mass as BMC/0.54 (12,37). The collected data was used to evaluate the scaling of body weight, ATFM, SM mass, and bone mass to height.…”

“…The study was approved by the Institutional Review Board of St. Luke's-Roosevelt Hospital, and all subjects signed an informed consent prior to participation. The NY Asian men were evaluated as part of a larger cross-sectional body composition study, and brain imaging studies were not included in the protocol (12,14,33).…”

“…Other than aging, once maximal brain mass is achieved in early adulthood there is relatively little change in brain size across the life span, with the exception perhaps of neural tissue loss secondary to severe semistarvation (36). On the other hand, body mass and most associated compartments can vary widely during adulthood, as for example the growth of adipose tissue, SM, bone, liver, and heart that occurs with the development of obesity (12,41). Hormones, such as growth hormone and IGF-1b, have minimal effects on postnatal brain mass but substantial effects on somatic tissues such as is observed in patients with acromegaly (6) or in transgenic rodent models overexpressing growth hormone (35).…”

Resting energy expenditure can be assessed by dual-energy X-ray absorptiometry in women regardless of age and fitness

“…The specific resting metabolic rate of the four compartments was assumed from previously reported data, bone (2.3 kcal kg À1 ), AT (4.5 kcal kg À1 ), skeletal muscle (13 kcal kg À1 ) and residual (53 kcal kg À1 ) (Holliday et al, 1967;Grande, 1989;Elia, 1992;Hayes et al, 2002;Heymsfield et al, 2002).…”

“…Recently, Hayes et al (2002) demonstrated that REE can be estimated from the summed heat productions from the weights of the brain, skeletal muscle mass (SM), adipose tissue (AT), bone and tissue organs by DXA. In view of the finding of Hayes et al (2002), we decided to evaluate the possibility that measurement of the magnitude and distribution of fundamental somatic heat-producing units using DXA can be used to estimate REE in both young and elderly women with different aerobic fitness levels.…”