Respiratory quotient: Effects of fatty acid composition.
Level 5 - mechanism / opinion, no new human data
Non-clinical stoichiometric modeling and narrative review of tissue composition (design analogy).
PubMed 33063463 · doi:10.1002/jez.2422
What was done
The authors calculated theoretical respiratory quotients (RQ) for various individual fatty acids and surveyed published fuel lipid fatty acid compositions across multiple vertebrate taxa to model how expected fasting lipid RQ varies by species and habitat.
What was found
Theoretical RQs for single fatty acids ranged from less than 0.7 (e.g., stearic acid) to greater than 0.76 (e.g., docosahexaenoic acid). Terrestrial fasting vertebrates averaged an expected lipid RQ of approximately 0.71. In contrast, aquatic and marine vertebrates, particularly fish, yielded lipid RQs up to 0.73 when oxidizing fat alone. Selective mobilization of fatty acids caused only negligible shifts in lipid RQ. The authors suggest using a lipid RQ of 0.725 for cold-water fish when specific fatty acid profiles are unavailable.
Why it matters
Applying the standard lipid RQ of 0.71 introduces systematic error in indirect calorimetry calculations for marine and aquatic organisms. Accounting for taxon- and habitat-specific fatty acid profiles improves the accuracy of substrate oxidation estimates.
Limits
The abstract describes stoichiometric modeling and a literature survey rather than direct empirical validation of gas exchange in live animals. The total number of taxa or studies surveyed is not reported in the abstract.
Cited by
- supports Combining cold stress with a calorie-restricted diet shifts the respiratory quotient (RQ) toward 0.7, indicating a shift toward fat oxidation.