Diet-induced thermogenesis and respiratory quotient after Roux-en-Y gastric bypass surgery: a prospective study

Studies in humans and other animals have shown that Roux-en-Y gastric bypass (RYGB) leads to increased energy expenditure (EE). We analyzed several components of EE, such as the respiratory quotient (RQ), resting metabolic rate (RMR), and diet-induced thermogenesis (DIT) among patients before and after RYGB.

In this prospective clinical study, RMR, DIT, and RQ were measured by indirect calorimetry (IC) in the same patients before and 12 months after RYGB (the preoperative and postoperative time points, respectively). Postprandial RQ and DIT were measured after patients consumed a standard ~270 kcal meal (62% carbohydrates, 12% proteins, and 26% lipids).

The population studied consisted of 13 patients (mean age 40.8 ± 6.7 years, 85% female).At the postoperative (postop) time point, patients showed higher weight-adjusted RMR compared with the preoperative (preop) time point (P<.01). The absolute and weight-adjusted metabolic rates 20 minutes after the meal were increased postoperatively (P<.0001) but not preoperatively (P = 0.2962) (DIT); this increase in RQ was significantly higher in the postop than in the preop time point.

The observed patients showed increased EE, DIT, and RQ after RYGB surgery. These data may serve as important physiologic factors contributing to the loss and maintenance of weight after RYGB.