Postabsorptive respiratory quotient and food quotient-an analysis in lean and obese men and women.

OBJECTIVE: Macronutrient intake is difficult to measure under free-living conditions, because of errors in the reporting of food intake. The aim of the current study was to assess whether postabsorptive respiratory quotient (RQ) is indicative for the food quotient (FQ), with other factors, such as body composition and energy balance, taken into account.
SUBJECTS: Thirty lean subjects (age 31+/-9 y, body mass index (BMI) 22.0+/-2.1 kg/m2) and 20 obese subjects (age 48+/-12 y, BMI 33.3+/-4.4 kg/m2) participated in the study.
DESIGN: Body mass changes were determined over a 7 day period before the measurement of postabsorptive RQ and in this period subjects reported their total food intake in a dietary record. A subgroup of 12 lean subjects was supplied with their total food intake in this period (twice with different diets). Food quotients were calculated from the valid food records (<10% underrecording and undereating). Body composition was estimated using the three-compartment model of Siri.
RESULTS: Postabsorptive RQ was not related to FQ (n=31, r=-0.24, P=0.2) and no difference was observed between the two diet periods (n=12 paired t-test, P=0.9). Postabsorptive RQ was related to the change in body mass (r=0.57, P=0.0001), but not to BMI, fat mass or fat-free mass.
CONCLUSIONS: In the present study, the energy balance over the days prior to the measurement was the most important factor influencing postabsorptive RQ. Postabsorptive RQ was not a reliable indicator for habitual FQ even when corrected for energy balance and body composition.