Models of energy homeostasis in response to maintenance of reduced body weight.

OBJECTIVE: To test three proposed models for adaptive thermogenesis in compartments of energy expenditure following different degrees of weight loss. Specifically, (1) there is no adaptive thermogenesis [constant relationship of energy expenditure (EE) to metabolic mass]. (2) There is a fixed degree of adaptive thermogenesis once fat stores are below a "threshold." (3) The degree of adaptive thermogenesis is proportional to weight loss.

METHODS: The relationship between weight loss and EE was examined in 17 inpatient subjects with stable weight and obesity studied at usual weight and again following a 10% and a 20% weight loss.

RESULTS: Following initial weight loss (10%), resting (REE) and non-resting (NREE) EE were significantly below those predicted on the basis of the amount and composition of weight lost. Further reductions below predicted values of NREE but not REE occurred following an additional 10% weight loss. Changes in body weight, composition, and/or energy stores were significantly correlated with changes in EE.

CONCLUSIONS: All models are applicable to the decline in EE following weight loss. The disproportionate decline in REE is consistent with a threshold model (no change with further weight loss) while the disproportionate decline in NREE is largely reflective of the degree of weight loss.