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(1) 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 45 for adipose tissue and 12 for residual organs and tissues How ever Elia s K(1) values have never been fully evaluated Objectives The objectives of the present study were to evaluate the applicability of Elia s K(1) values across adulthood and to explore the potential influence of age on the K(1) values Design A new approach was developed to evaluate the K(1) values of major organs and tissues on the basis of a mechanistic model REE = Sigma(K(1) x T(1)) where REE is whole body resting energy expenditure measured by Indirect calorimetry and T(1) is the mass of individual organs and tissues measured by magnetic resonance imaging With measured REE and T(1) marginal 95% CIs for K(1) values were calculated by stepwise univariate regression analysis An existing data base of nonobese healthy adults [n= 131 body mass index (in kg/m(2)) <30] was divided into 3 age groups 21-30 y (young n = 43) 31-50 y (middle age n = 51) and >50 y (n = 37) Results Elia s K(1) values were within the range of 95% CIs in the young and middle age groups However Elia s K(1) values were outside the right boundaries of 95% CIs in the >50-y group which indicated that Elia s study overestimated K(1) values by 3% in this group Age adjusted K(1) values for adults aged >50 y were 194 for liver 233 for brain 426 for heart and kidneys 126 for skeletal muscle 44 for adipose tissue and 11 6 for residuals Conclusion The general applicability of Elia s K(1) values was validated across adulthood although age adjustment is appropriate for specific applications Am J Clin Nutr 2010 92 1369-77