title: Relationship between postabsorptive respiratory exchange ratio and plasma free fatty acid concentrations.
abstract: The relationship between overnight postabsorptive (fasting) respiratory exchange ratio (RER) and plasma FFA concentrations was addressed using data from three separate protocols, each of which involved careful control of the antecedent diet. Protocol 1 examined the relationship between fasting RER and the previous daytime RER. In Protocol 2 fasting, RER and plasma palmitate concentrations were measured in 29 women and 31 men (body mass index <30 kg.m(-2)). Protocol 3 analyzed data from Nielsen et al. (Nielsen, S., Z. K. Guo, J. B. Albu, S. Klein, P. C. O'Brien, M. D. Jensen. 2003. Energy expenditure, sex and endogenous fuel availability in humans. J. Clin. Invest. 111: 981-988.) to understand how fasting RER and palmitate concentrations relate within individuals during four consecutive measurements. The results were as follows: 1) Fasting RER was correlated (r = 0.74, P < 0.001) with the previous day's average RER, and less so with RER variability. 2) Fasting RER was correlated (r = -0.39, P = 0.007) with fasting plasma palmitate concentrations. 3) The pattern of the RER/palmitate relationship was similar within individuals and between individuals; a negative slope was observed significantly more often than a positive slope (chi(2) test; P < 0.001). Our findings suggest that, despite a fixed food quotient, the slight departures from energy equilibrium in a controlled General Clinical Research Center environment can effect plasma FFA concentrations. We suggest that including indirect calorimetry as part of FFA metabolism studies may aid in data interpretation.
authors.affiliation: Mayo Clinic, Rochester, MN, USA. jensen@mayo.edu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Jensen
authors.forename: Jirí
authors.initials: J
authors.lastname: Bajnárek
authors.forename: Sang Yeoup
authors.initials: SY
authors.lastname: Lee
authors.forename: Soren
authors.initials: S
authors.lastname: Nielsen
authors.forename: Christina
authors.initials: C
authors.lastname: Koutsari
mesh_terms: D000293:Adolescent; D000328:Adult; D001823:Body Composition; D004837:Epinephrine / Q000097:blood; D005215:Fasting / Q000097:blood* / Q000378:metabolism / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005260:Female; D005502:Food; D005947:Glucose / Q000378:metabolism; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D008875:Middle Aged; D010168:Palmitates / Q000097:blood; D012119:Respiration; D013997:Time Factors; D055815:Young Adult
chemical_list: D005230:Fatty Acids, Nonesterified; D007328:Insulin; D010168:Palmitates; D019382:Human Growth Hormone; D005947:Glucose; D004837:Epinephrine