Effect of energy restriction on total heat production, basal metabolic rate, and specific dynamic action of food in rats.

Man and experimental animals are able to adapt to restricted levels of energy intake mainly by a reduction in basal metabolic rate (BMR) while the effects of energy restriction on the specific dynamic action (SDA) of food and the spontaneous activity are less well established. In this study, growing rats were fed ad libitum or restricted amounts of diet during 28-31 days. Then total heat production (THP) and BMR during 22 hours, as well as SDA of a test meal, were measured on individual rats by indirect calorimetry. After the calorimeter study rats were kept in metabolic cages for 6 days after which they were killed and analyzed for total body composition. The energy balance of the rats over the last 7 days of the study was calculated from changes in body composition and measurements of food intake during this period. During the calorimeter experiment an indirect estimation of the spontaneous activity of the rat was made. Results showed that THP, BMR and SDA of restricted rats were significantly lower than for ad libitum-fed rats. From body composition measurements, rats restricted in food intake before the calorimetry study were found to mobilize more protein and less fat compared to rats fed ad libitum until the calorimetry and body composition studies were carried out. No difference in spontaneous activity was observed between the two dietary treatments.