The biological responses to caloric restriction (CR) are generally examined in rats with elevated metabolic rates due to being housed at ambient temperatures (T_a) below the zone of thermoneutrality. We determined the physiological and behavioral responses to two weeks of 30-40% CR in male FBNF1 rats housed in cool (T_a=12°C) or thermoneutral (TMN; T_a=30°C) conditions. Rats were instrumented with telemetry devices and housed continuously in homecage calorimeters for the entire experiment. At baseline, rats housed in cool Ta had reduced rate of weight gain, thus a mild CR (5%) group at thermoneutrality for weight maintenance was also studied. Rats housed in cool T_a exhibited elevated caloric intake (cool= 77±1; TMN= 54±2 kcals), oxygen consumption (VO₂; cool= 9.9±0.1; TMN=5.5±0.1 ml/min), mean arterial pressure (cool= 103±1; TMN= 80±2 mmHg), and heart rate (cool=374±3; TMN= 275±4 bpm). Cool-CR rats exhibited greater CR-induced weight loss (cool= -62±3; TMN= -42±3 g) and reductions in VO₂ (cool= -2.6±0.1; TMN= -1.5±0.1 ml/min), but similar CR-induced reductions in heart rate (cool= -59±1; TMN= -51±7 bpm). CR had no effect on arterial blood pressure or locomotor activity in either group. Unexpectedly, weight maintenance produced significant reductions in VO₂ and heart rate. At thermoneutrality , a single day of refeeding effectively abolished CRinduced reductions in VO₂ and heart rate. The results reveal that rats with low or high baseline metabolic rate exhibit comparable compensatory reductions in VO₂ and heart rate and suggest that T_a can be used to modulate the metabolic background upon which the more prolonged effects of CR can be studied.