Thermogenic changes after gastric bypass, adjustable gastric banding or diet alone.

Background: The mechanisms by which bariatric surgery achieves weight loss (WL) are under scrutiny. We assessed changes in resting energy expenditure (REE) after gastric bypass (RYGB) and gastric banding (AGB) to determine if changes in REE are associated with WL and type of surgery.

Methods: Three groups of morbidly obese patients were studied: RYGB (n = 12), AGB (n = 8), and a control group that underwent caloric restriction alone (Diet, n = 10). Studies were performed at baseline and after 14 days in all groups and 6 months after RYGB and AGB. REE (kcal/day) was measured by indirect calorimetry and adjusted for body weight (Wt-REE), and lean body mass by dual-energy X-ray absorptiometry (LBM-REE).

Results: At baseline, REE did not differ significantly among groups (RYGB = 2,114 ± 337, AGB = 1,837 ± 154, Diet = 2,091 ± 363 kcal/day, P = .13). After 14 days, the groups had similar percent excess WL (%EWL). Neither Wt-REE nor LBM-REE changed significantly in any group. After 6 months %EWL was 49 ± 10% after RYGB and 21 ± 11% after AGB (P < .01); RYGB patients had greater increase in the percent of weight that was LBM (RYGB = 7.9 ± 3.0 vs. AGB = 1.6 ± 1.5%, P < .01). Wt-REE increased significantly only after RYGB (+2.58 ± 1.51 kcal/kg/day, P < .01). There was a significant correlation between changes in Wt-REE and %EWL (r = 0.670, P = .003).

Conclusion: The increase in Wt-REE may be a factor supporting WL after RYGB.