The effects of graded levels of calorie restriction: III. Impact of short term calorie and protein restriction on mean daily body temperature and torpor use in the C57BL/6 mouse

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.