Metabolic rate of major organs and tissues in young adult South Asian women

Background/Objectives: Major organ-specific and tissue-specific metabolic rate (K_i) values were initially estimated using in vivo methods, and values reported by Elia (Energy metabolism: tissue determinants and cellular corollaries, Raven Press, New York, 1992) were subsequently supported by statistical analysis. However, the majority of work to date on this topic has addressed individuals of European descent, whereas population variability in resting energy metabolism has been reported. We aimed to estimate K_ivalues in South Asian females. Subjects/Methods: This cross-sectional study recruited 70 healthy young women of South Asian ancestry. Brain and organs were measured using magnetic resonance imaging, skeletal muscle mass by dual-energy X-ray absorptiometry, fat mass by the 4-component model, and whole-body resting energy expenditure by indirect calorimetry. Organ and tissue K_ivalues were estimated indirectly using regression analysis through the origin. Preliminary analysis suggested overestimation of heart mass, hence the modeling was repeated with a literature-based 22.5% heart mass reduction. Results: The pattern of derived K_ivalues across organs and tissues matched that previously estimated in vivo, but the values were systematically lower. However, adjusting for the overestimation of heart mass markedly improved the agreement. Conclusions: Our results support variability in K_ivalues among organs and tissues, where some are more metabolically “expensive” than others. Initial findings suggesting lower organ/tissue K_ivalues in South Asian women were likely influenced by heart mass estimation bias. The question of potential ethnic variability in organ-specific and tissue-specific energy metabolism requires further investigation.