Blunting of adaptive thermogenesis as a potential additional mechanism to promote weight loss after gastric bypass.

Background: Adaptive thermogenesis (AT) is described as a change in resting metabolic rate (RMR) that is greater than would be predicted from changes in lean body mass (LBM) and fat mass (FM) alone during periods of energy imbalance. Whereas an AT-related downregulation of RMR has been implicated in suboptimal weight loss and weight regain after nonsurgical weight loss, defense against AT may underpin the durable weight loss after laparoscopic Roux-en-Y gastric bypass (LRYGB) and other bariatric surgeries. However, methodological differences across the few studies that have evaluated postoperative AT limit interpretation as to the effects of these procedures on RMR.

Objective: To quantify AT 6 months after LRYGB and laparoscopic adjustable gastric banding (LAGB).

Setting: The study was conducted in a large university hospital in the United States.

Methods: Changes in body composition and RMR were assessed in 13 severely obese adults 6 months after LRYGB (n = 8) and LAGB (n = 5). AT was calculated as the difference between measured RMR and RMR predicted from LBM, FM, age, and sex before and after surgery.

Results: RMR significantly decreased after LRYGB (-270±96 kcal/d, P<.01) but not after LAGB. Despite significantly greater reductions in weight, FM, and LBM with LRYGB than LAGB, AT responses after LRYGB (15±110 kcal/d, P = .7) and LAGB (42±97 kcal/d, P = .4) were similar (P = .7).

Conclusion: Despite significant weight and body composition changes, AT was minimal after LRYGB. A blunting of AT may be an additional mechanism that favors sustainable weight loss with LRYGB.