Effects of long-term dietary restriction on body temperature are modified with increasing age

Effects of long-term dietary restriction on body temperature and its circadian changes were investigated in 3.5- and 14.5-month-old male Long-Evans rats. Animals were either fed and libitum or kept on a restricted diet for 8 weeks. Purina Lab Chow was constantly available to the ad libitum-fed groups, while half portions of their daily food consumption were given to age-matched diet-restricted groups every day. A highly significant lowering of body temperature in middle-aged diet-restricted (MR) rats was not observed until their food intake had been restricted for 5 weeks compared with that of the middle-aged ad libitum-fed (MA) group as well as that of the young diet-restricted (YR) rats. Eight weeks after diet restriction, both the circadian pattern of body temperature and its diurnal peak-trough difference remained almost unchanged in all four groups, while the average body temperature of MR rats was greatly lower than that of the YR group and that of MA animals. No significant difference in average body temperature was found between the young ad libitum-fed (YA) rats and the MA group. These data suggest that the average body temperature and its circadian changes in ad libitum-fed rats, at least before the age of 14.5 months, is not age-related, while the effect of dietary restriction on body temperature may be modified with increasing age.