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(i); 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, 4.5 for adipose tissue, and 12 for residual organs and tissues. However, Elia's K(i) values have never been fully evaluated.


OBJECTIVE
The objectives of the present study were to evaluate the applicability of Elia's K(i) values across adulthood and to explore the potential influence of age on the K(i) values.


METHODS
A new approach was developed to evaluate the K(i) values of major organs and tissues on the basis of a mechanistic model: REE = Σ(K(i) × T(i)), where REE is whole-body resting energy expenditure measured by indirect calorimetry, and T(i) is the mass of individual organs and tissues measured by magnetic resonance imaging. With measured REE and T(i), marginal 95% CIs for K(i) values were calculated by stepwise univariate regression analysis. An existing database of nonobese, healthy adults [n = 131; body mass index (in kg/m²) <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(i) values were within the range of 95% CIs in the young and middle-age groups. However, Elia's K(i) values were outside the right boundaries of 95% CIs in the >50-y group, which indicated that Elia's study overestimated K(i) values by 3% in this group. Age-adjusted K(i) values for adults aged >50 y were 194 for liver, 233 for brain, 426 for heart and kidneys, 12.6 for skeletal muscle, 4.4 for adipose tissue, and 11.6 for residuals.


CONCLUSIONS
The general applicability of Elia's K(i) values was validated across adulthood, although age adjustment is appropriate for specific applications.
Wang
Zimian
Z
Obesity Research Center, St Luke's-Roosevelt Hospital, Columbia University, College of Physicians and Surgeons, New York, NY, USA. zw28@columbia.edu
Ying
Zhiliang
Z
Bosy-Westphal
Anja
A
Zhang
Junyi
J
Schautz
Britta
B
Later
Wiebke
W
Heymsfield
Steven B
SB
Müller
Manfred J
MJ
D000273:Adipose Tissue / Q000502:physiology; D000328:Adult; D000367:Age Factors; D001481:Basal Metabolism / Q000502:physiology*; D001921:Brain / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006321:Heart / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000502:physiology; D008099:Liver / Q000502:physiology; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology; D012016:Reference Values; D012044:Regression Analysis; D055815:Young Adult