LAUSR

Background/objectives The ability to adapt the level of daily fuel utilization to substrate availability is given by the respiratory quotient (RQ), which its variance is an indicator of metabolic flexibility. Metabolic inflexibility is associated with many pathologies including obesity, but evidence relies on bed-rest studies and exercise-based interventions. Our goal was to examine the associations for RQ variance in response to daily living activities with obesity, in healthy adults. Subjects/methods Participants ( N  = 50; 25 women), 20–64 years were lying for 60 min and randomly performed three conditions for 10 min each (sitting, standing, 1 sit/stand/sit transition min −1 ). RQ was measured by indirect calorimetry and fat mass (FM), trunk FM (TFM), and fat-free mass (FFM) by DXA. Results RQ variance among the three conditions was inversely associated with BMI ( ß  = 0.005; p  < 0.001), FM ( ß  = 0.007; p  = 0.024), and TFM ( ß  = 0.008; p  = 0.026). A positive association was found between RQ variance and FFM ( ß  = −0.007; p  = 0.024). No interactions for sex were found ( p  ≥ 0.05). Conclusions These findings suggest that a higher RQ variance in response to daily living metabolic challenges such as transitioning between sitting and standing is associated with lower overall and central obesity, as well as with a higher FFM, in healthy adults. Thus, RQ variance may work as an indication of metabolic flexibility, but these findings were obtained in a young and non-obese adult population without considering their fitness levels. Thus, further research in this field is warranted.