DISSOCIATION BETWEEN FOOD-INTAKE, DIET COMPOSITION, AND METABOLISM INPARABIOTIC PARTNERS OF OBESE RATS

When one member of a parabiosed pair of rats is overfed, its ad libitu m-fed partner loses body fat in the absence of a statistically signifi cant decrease in food intake. Three experiments investigated the relat ionships between food intake, metabolism, and body composition in this model. In vivo measurement of lipogenesis confirmed that loss of fat is associated with decreased fat deposition. When partners of overfed rats were compared with food-restricted single rats, proportional chan ges in body composition and metabolism were similar for the two treatm ents, although there was no significant change in the food intake of p arabiotic rats, whereas restricted rats received only 60% of the intak e of their controls. The final experiment demonstrated that changes in body composition of partners of overfed rats were independent of diet ary composition. These results suggest that, when a rat is made obese by overfeeding, a circulatory factor is released that inhibits fat dep osition and disrupts regulatory mechanisms that normally stimulate foo d intake during a period of negative energy balance.