Evaluation of Specific Metabolic Rates of Major Organs and Tissues: Comparison Between Nonobese and Obese Women

Elia (1992) identified the specific resting metabolic rates (K-i) of major organs and tissues in young adults with normal weight: 200 for liver, 240 for brain, 440 for heart and kidneys, 13 for skeletal muscle, 4.5 for adipose tissue and 12 for residual mass (all units in kcal/kg per day). The aim of the present study was to assess the applicability of Elia's K-i values for obese adults. A sample of young women (n = 80) was divided into two groups, nonobese (BMI <29.9 kg/m(2)) and obese (BMI 30.0-43.2 kg/m(2)). This study was based on the mechanistic model: REE = Sigma (K-i x 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. For each organ/tissue, the corresponding Elia's K-i value was analyzed respectively for nonobese and obese groups by using stepwise univariate regression analysis. Elia's K-i values were within the range of 95% confidence intervals (CIs) in the nonobese group. However, Elia's K-i values were outside the right boundaries of 95% CIs in the obese group and a corresponding obesity-adjusted coefficient was calculated as 0.98, indicating that Elia's values overestimate K-i by 2.0% in obese adults. Obesity-adjusted K-i values were 196 for liver, 235 for brain, 431 for heart and kidneys, 12.7 for skeletal muscle, 4.4 for adipose tissue, and 11.8 for residual mass. In conclusion, although Elia's K-i values were validated in nonobese women, obesity-adjustments are appropriate for application in obese women.