Resting metabolic rate, total daily energy expenditure, and metabolic adaptation 6-months and 24-months after bariatric surgery

OBJECTIVE: Little is known about long-term metabolic (energy expenditure) adaptation after bariatric surgery. METHODS: Resting metabolic rate under basal conditions (RMR), total daily energy expenditure (TDEE) and body composition were measured in 25 participants in the Longitudinal Assessment of Bariatric Surgery-2 (LABS-2). RESULTS: Six months after surgery, BMI (±SD) decreased (47 ± 6 to 37 ± 5 kg/m(2)), body fat from 48 ± 6 to 40 ± 6% fat and fat-free mass from 67 ± 9 to 60 ± 9 kg. In absolute terms RMR and TDEE both decreased significantly (1730 ± 278 vs. 1430 ± 200 and 2879 ± 544 vs. 2369 ± 304 kcal/day) and the achieved energy balance was −1293 ± 355 kcal/day. Sixteen of these participants underwent repeated measures at ~24 months; TDEE decreased 6 months postoperative (2957 ± 540 kcal/day to 2423 ± 324, P=0.0003), but at ~24 months, TDEE (2602 ± 471 kcal/day) was not significantly different compared to Month 6. The average negative energy balance from Baseline to Month 24 was −379 ± 131 kcal/day. CONCLUSIONS: RMR and TDEE fall precipitously in the first six months after bariatric surgery but these adaptive changes were no longer significant after two years.