Mass-specific basal metabolic rate (mass-specific BMR), defined as the resting energy expenditure per unit body mass per day, is an important parameter in energy metabolism research. However, a mechanistic explanation for magnitude of mass-specific BMR remains lacking. The objective of the present study was to validate the applicability of a proposed mass-specific BMR model in healthy adults. A mechanistic model was developed at the organ-tissue level, mass-specific BMR = Σ(Ki × Fi), where Fi is the fraction of body mass as individual organs and tissues, and Ki is the specific resting metabolic rate of major organs and tissues. The Fi values were measured by multiple MRI scans and the Ki values were suggested by Elia in 1992. A database of healthy non-elderly non-obese adults (age 20 - 49 yrs, BMI <30 kg/m2) included 49 men and 57 women. Measured and predicted mass-specific BMR of all subjects was 21.6 ± 1.9 (mean ± SD) and 21.7 ± 1.6 kcal/kg per day, respectively. The measured mass-specific BMR was correlated with the predicted mass-specific BMR (r = 0.82, P <0.001). A Bland-Altman plot showed no significant trend (r = 0.022, P = 0.50) between the measured and predicted mass-specific BMR, versus the average of measured and predicted mass-specific BMR. In conclusion, the proposed mechanistic model was validated in non-elderly non-obese adults and can help to understand the inherent relationship between mass-specific BMR and body composition.
Keywords: magnetic resonance imaging; organ; specific resting metabolic rate; tissue.