Background/Objectives: In this study, we ascertained the relationship between resting energy expenditure (REE) obtained using two procedures: indirect calorimetry and from organ-tissue mass, calculated employing magnetic resonance imaging (MRI), and adult metabolic rate constants, in prepubertal children. Differences between the measured and the calculated REEs were assessed according to age at puberty approaching stage. Subjects/Methods: We recruited 6–12 years old 110 healthy Japanese prepubertal children (40 girls and 70 boys). Organ-tissue masses for different organs (skeletal muscle, liver, kidneys, brain and adipose tissue) were determined using MRI and dual-energy X-ray absorptiometry. Heart and residual masses were calculated on the basis of each equation. REE was measured using the Douglas bag technique (measured REE). On the other hand, calculated REE was obtained by multiplying the sum of body compartments with the corresponding adult tissue respiration rate. Results: The measured REE was significantly greater than the calculated REE in both, boys and girls, although a significant association was noticed between the two REEs in both the sexes. Besides, correlation between age and difference in the two REEs was found to be significant only in girls. Conclusions: The present study revealed that: (1) measured and calculated REEs differ by approximately 300 kcal/day in a relatively large sample of prepubertal children, and (2) the difference in organ-tissue mass between the measured and calculated REEs increased from approximately 200 to 400 kcal/day during the developmental process in girls but not in boys.
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