Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.

ObjectiveTo measure resting metabolic rate (RMR) and body composition changes in obese subjects following massive weight loss achieved via bariatric surgery or calorie restriction plus vigorous exercise.Design and MethodsWe compared changes in body composition and RMR in 13 pairs of obese subjects retrospectively matched for sex, body mass index, weight and age that underwent either Roux-en-Y gastric bypass surgery (RYGB) or participated in “The Biggest Loser” weight loss competition (BLC).ResultsBoth groups had similar final weight loss (RYGB: 40.2 ± 12.7 kg, BLC: 48.8 ± 14.9 kg; p=0.14); however, RYGB lost a larger proportion of their weight as fat-free mass (FFM) (RYGB: 30 ± 12%, BLC: 16 ± 8% [p<0.01]). In both groups, RMR decreased significantly more than expected based on measured body composition changes. The magnitude of this metabolic adaptation was correlated with the degree of energy imbalance (r = 0.64, p =0.003) and the decrease in circulating leptin (r = 0.61, p=0.006).ConclusionsCalorie restriction along with vigorous exercise in BLC participants resulted in preservation of FFM and greater metabolic adaption compared to RYGB subjects despite comparable weight loss. Metabolic adaptation was related to the degree of energy imbalance and the changes in circulating leptin.

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