Validity of predictive equations for resting metabolic rate in healthy humans

Background: There are several predictive equations for estimating resting metabolic rate (RMR) in healthy humans. Concordance of these equations against measured RMR is variable, and often dependent on the extent of RMR. Part of the discrepancy may be due to an insufficient accuracy of metabolic carts, but this accuracy can be improved via a correction procedure. Objective: To determine the validity of predictive RMR equations by comparing them against measured and corrected (i.e. the reference) RMR. Methods: RMR was measured, in 69 healthy volunteers (29 males/40 females; 32+- 8 years old; BMI 25.5+- 3.8 kg/m²) and then corrected by simulating gas exchange through pure gases and high-precision mass-flow regulators. RMR was predicted using 13 published equations. Bland-Altman analyses compared predicted vs. reference RMRs. Results: All equations correlated well with the reference RMR (r > 0.67; P < 0.0001), but on average, over-predicted the reference RMR (89-312 kcal/d; P < 0.05). Based on Bland-Altman analyses, 12 equations showed a constant bias across RMR, but the bias was not different from zero for nine of them. Three equations stood out because the absolute difference between predicted and reference RMR was equal or lower than 200 kcal/d for > 60% of individuals (the Mifflin, Oxford and Müller equations). From them, only the Oxford equations performed better in both males and females separately. Conclusion: The Oxford equations are a valid alternative to predict RMR in healthy adult humans. Gas-exchange correction appears to be a good practice for the reliable assessment of RMR.