How Rats Economize: Energy Loss in Starvation

Adaptation of energy expenditure to partial or complete food deprivation was studied in the laboratory rat. Energy expenditure was measured by means of a material balance technique and with indirect calorimetry. Increasing the temporal resolution of the latter method and combining it with other techniques allowed a detailed analysis of expenditure into its components. All experiments were done at a temperature of 30 C. Total expenditure during food deprivation went down by nearly three-fifths of its ad lib. value. Of the total decrease of 59%, 12%-13%, was due to cessation of food processing, 12% to reduction of activity, and 34%-35% to a drop of fasting resting metabolic rate. Finally the consequences of the expenditure changes for the regulation of body temperature were studied. The mean core temperature fell by 1 C while the animals reduced their thermal conductance. The adaptive significance of the findings is discussed.