A commonly observed response in mammals to calorie restriction (CR) is reduced body temperature (T b). We explored how the T b of male C57BL/6 mice responded to graded CR (10 to 40%), compared to the response to equivalent levels of protein restriction (PR) over 3 months. Under CR there was a dynamic change in daily T b over the first 30–35 days, which stabilized thereafter until day 70 after which a further decline was noted. The time to reach stability was dependent on restriction level. Body mass negatively correlated with T b under ad libitum feeding and positively correlated under CR. The average T b over the last 20 days was significantly related to the levels of body fat, structural tissue, leptin and insulin-like growth factor-1. Some mice, particularly those under higher levels of CR, showed periods of daily torpor later in the restriction period. None of the changes in T b under CR were recapitulated by equivalent levels of PR. We conclude that changes in T b under CR are a response only to the shortfall in calorie intake. The linear relationship between average T b and the level of restriction supports the idea that T b changes are an integral aspect of the lifespan effect.