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.

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Background: After weight loss, total energy expenditure-in particular, energy expenditure at low levels of physical activity-is lower than predicted by actual changes in body weight and composition. An important clinical issue is whether this reduction, which predisposes to weight regain, persists over time. Objective: We aimed to determine whether this disproportionate reduction in energy expenditure persists in persons who have maintained a body-weight reduction of ͧ10% for 1 y. Design: Seven trios of sex-and weight-matched subjects were studied in an in-patient setting while receiving a weight-maintaining liquid formula diet of identical composition. Each trio consisted of a subject at usual weight (Wt initial ), a subject maintaining a weight reduction of ͧ10% after recent (5-8 wk) completion of weight loss (Wt loss-recent ), and a subject who had maintained a documented reduction in body weight of 10% for 1 y (Wt loss-sustained ). Twentyfour-hour total energy expenditure (TEE) was assessed by precise titration of fed calories of a liquid formula diet necessary to maintain body weight. Resting energy expenditure (REE) and the thermic effect of feeding (TEF) were measured by indirect calorimetry. Nonresting energy expenditure (NREE) was calculated as NREE ҃ TEE -(REE ѿTEF). Results: TEE, NREE, and (to a lesser extent) REE were significantly lower in the Wt loss-sustained and Wt loss-recent groups than in the Wt initial group. Differences from the Wt initial group in energy expenditure were qualitatively and quantitatively similar after recent and sustained weight loss. Conclusion: Declines in energy expenditure favoring the regain of lost weight persist well beyond the period of dynamic weight loss.Am J Clin Nutr 2008;88:906 -12.