Objective:To evaluate the possibility that measurement of the magnitude and distribution of fundamental somatic heat-producing units using dual-energy X-ray absorptiometry (DXA) can be used to estimate resting energy expenditure (REE) in both young and elderly women with different aerobic fitness levels. Subjects and methods: Peak oxygen uptake (VO2 peak) and REEm were directly measured in 116 young (age: 22.3 ± 2.1 years) and 72 elderly (63.3 ± 6.4 years) women. The subjects were divided into four groups according to categories of age and VO2 peak; young: high fitness (YH, n=58); low fitness (YL, n=58); elderly: high fitness (EH, n=37) and low fitness (EL, n=35). Using DXA, systemic and regional body compositions were measured, and REEe was estimated from the sum of tissue organ weights multiplied by corresponding metabolic rate. Results: Although there were remarkable differences in systemic and regional body compositions, no significant differences were observed between REEm and REEe in the four groups. REEe significantly correlated with REEm in elderly as well as young women; the slopes and intercepts of the two regression lines were statistically not different between the elderly and young groups (elderly: y=0.60x+472, r=0.667; young: y=0.78x+250, r=0.798; P<0.001, respectively). A Bland-Altman analysis did not indicate bias in calculation of REE for all the subjects. Conclusion: These results suggest that REE can be estimated from tissue organ components in women regardless of age and aerobic fitness.
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