Changes in Energy Expenditure Resulting from Altered Body Weight

Abstract

Background. No current treatment for obesi- ty reliably sustains weight loss, perhaps because com- pensatory metabolic processes resist the maintenance of the altered body weight. We examined the effects of ex- perimental perturbations of body weight on energy ex- penditure to determine whether they lead to metabolic changes and whether obese subjects and those who have never been obese respond similarly. Methods. We repeatedly measured 24-hour total en- ergy expenditure, resting and nonresting energy expend- iture, and the thermic effect of feeding in 18 obese sub- jects and 23 subjects who had never been obese. The subjects were studied at their usual body weight and after losing 10 to 20 percent of their body weight by underfeed- ing or gaining 10 percent by overfeeding. Results. Maintenance of a body weight at a level 10 percent or more below the initial weight was associated with a mean ( ! SD) reduction in total energy expenditure of 6 ! 3 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P 0.001) and 8 ! 5 kcal per kilogram per day in the obese subjects (P 0.001). Resting energy expenditure and nonresting energy expenditure each decreased 3 to 4 kcal per kilo- gram of fat-free mass per day in both groups of subjects. Maintenance of body weight at a level 10 percent above the usual weight was associated with an increase in total energy expenditure of 9 ! 7 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P 0.001) and 8 ! 4 kcal per kilogram per day in the obese subjects (P 0.001). The thermic effect of feeding and nonresting energy expenditure increased by approx- imately 1 to 2 and 8 to 9 kcal per kilogram of fat-free mass per day, respectively, after weight gain. These changes in energy expenditure were not related to the degree of ad- iposity or the sex of the subjects. Conclusions. Maintenance of a reduced or elevated body weight is associated with compensatory changes in energy expenditure, which oppose the maintenance of a body weight that is different from the usual weight. These compensatory changes may account for the poor long- term efficacy of treatments for obesity. (N Engl J Med 1995;332:621-8.)