The recovery of body weight after substantial weight loss or growth retardation is often characterized by a disproportionately higher rate of fat mass vs lean mass recovery, with this phenomenon of 'preferential catch-up fat' being contributed by energy conservation (thrifty) metabolism. To test the hypothesis that a low core body temperature (Tc) constitutes a thrifty metabolic trait underlying the high metabolic efficiency driving catch-up fat, the Anipill® system - with the telemetry capsules implanted in the peritoneal cavity - was used for continuous monitoring of Tc for several weeks in a validated rat model of semistarvation-refeeding in which catch-up fat is driven solely by suppressed thermogenesis. In animals housed at 22°C, 24h Tc was reduced in response to semistarvation (-0.77°C, p<0.001), and remained significantly lower than in controls during the catch-up fat phase of refeeding (-0.27°C on average, p<0.001); the lower Tc during refeeding being more pronounced during the light phase than during the dark phase of the 24h cycle (-0.30°C vs -0.23°C, p<0.01), and with no between-group differences in locomotor activity. A lower 24h Tc in animal showing catch-up fat was also observed when the housing temperature was raised to 29°C (i.e. at thermoneutrality). The reduced energy cost of homeothermy in response to caloric restriction persists during weight recovery, and constitutes a thrifty metabolic trait that contributes to the high metabolic efficiency that underlies the rapid restoration of the body's fat stores during weight regain, with implications for obesity relapse after therapeutic slimming and the pathophysiology of catch-up growth.