BackgroundReduction in energy expenditure during fasting and chronic food restriction is well known and represents a mechanism of energy conservation, sparing energy, and preventing excessive weight and energy loss. The present study aimed to investigate if obesity can alter the reduction in energy expenditure that occurs in response to chronic food restriction, using two different experimental models that promote distinct types of obesity.MethodsFemale Wistar rats were submitted to two models of obesity: hypercaloric diet ingestion (HD) and bilateral lesion of ventromedial hypothalamus (VMHL). Thirty days after the beginning of each treatment (HD and VMHL), the control and obese animals were subdivided in two groups that ingested for 30 days ad libitum diet or 50% of food ingested by the respective ad libitum group (control or obese). At the end of this period, the animals were euthanized, and the energy balance and body composition were determined.ResultsObese animals (HD and VMHL) showed increase on their body fat, confirming the effectiveness of the models in obesity development. When submitted to food restriction, control and obese animals showed a significant reduction in body weight and energy, metabolizable energy intake, energy expenditure, gross food efficiency, and body fat content, when compared with their respective ad libitum groups. Energy expenditure reduction shown by obese food-restricted animals for both models was significantly lower than the one shown by non-obese food-restricted groups.ConclusionObesity reduces the “sparing of energy” in food-restricted animals, suggesting that fat availability is one of the modulators of this mechanism; moreover, this physiologic adaptation should be considered in clinical nutrition protocols.