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Publication
Validation of an equation for energy expenditure that does not require the
respiratory quotient.
Authors Kaiyala KJ, Wisse BE, Lighton JRB
Submitted By Submitted Externally on 11/24/2019
Status Published
Journal PLoS ONE
Year 2019
Date Published
Volume : Pages 14 : e0211585
PubMed Reference 30707737
Abstract Energy expenditure (EE) calculated from respirometric indirect calorimetry is
most accurate when based on oxygen consumption (VO2), carbon dioxide production
(VCO2) and estimated protein metabolism (PM). EE has a substantial dependence of
~7% on the respiratory quotient (RQ, VCO2/VO2) and a lesser dependence on PM,
yet many studies have instead estimated EE from VO2 only while PM has often been
ignored, thus reducing accuracy. In 1949 Weir proposed a method to accurately
calculate EE without using RQ, which also adjusts for estimated PM based on
dietary composition. This RQ- method utilizes the calorimeter airflow rate (FR),
the change in fractional O2 concentration (?FO2) and the dietary protein
fraction. The RQ- method has not previously been empirically validated against
the standard RQ+ method using both VO2 and RQ. Our aim was to do that., VO2 and
VCO2 were measured repeatedly in 8 mice fed a high protein diet (HPD) during
exposure to different temperatures (n = 168 measurements of 24h gas exchange).
The HPD-adjusted RQ+ equation was: EE [kcal/time] = VO2 [L/time]×(3.853+1.081RQ)
while the corresponding RQ- equation was: EE = 4.934×FR×?FO2. Agreement was
analyzed using the ratios of the RQ- to RQ+ methods along with regression and
Bland-Altman agreement analyses. We also evaluated the standard equation using
the dietary food quotient (FQ) of 0.91 as a proxy for RQ (FQ+ method)., Ratio
analysis revealed that the mean error of the RQ- method was only 0.11 ± 0.042%
while the maximum error was only 0.21%. Error using the FQ+ method was 4 -and
10-fold greater, respectively. Bland-Altman analysis demonstrated that the RQ-
method very slightly overestimates EE as RQ decreases. Theoretically, this error
can be eliminated completely by imposing an incurrent fractional oxygen
concentration at a value only slightly greater than the atmospheric level., The
Weir 'RQ-free' method for calculating EE is a highly valid alternative to the
'gold standard' method that requires RQ. The RQ- approach permits reduced cost
and complexity in studies focused on EE and provides a way to rescue EE
measurement in studies compromised by faulty CO2 measurements. Practitioners of
respirometry should consider adjusting EE calculations for estimated protein
metabolism based on dietary composition.




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