Abstract
After a period of forced overfeeding, many individuals actively compensate for this weight gain by reducing food intake and maintaining this state of hypophagia well into the post-overfeeding period. Our central goal is to define the mechanism underlying this adaptive reduction in food intake. When male Long Evans rats were implanted with indwelling gastric cannula and overfed a liquid low-fat (10% fat) diet for 17 days, overfed rats exhibited increased weight gain (P<0.01) but decreased food intake, and this hypophagia persisted for 4-6 days post-overfeeding (P<0.05). Leptin levels were increased 8-fold by overfeeding (P<0.01), yet returned to baseline within 2 days post-overfeeding, despite the persistent hypophagia. Energy expenditure and oxygen consumption (VO2) were increased on the first day post-overfeeding (P<0.05), but subsequently normalized prior to the normalization of food intake. Lastly, in leptin receptor deficient Obese Zucker (fa/fa) rats, overfeeding produced a significant decrease in food intake during active overfeeding. However, food intake returned to near baseline levels within one day post-overfeeding. Contrastingly, food intake remained suppressed in lean controls for 6 days post-overfeeding. Thus intact leptin signaling is not required for the decrease in food intake that occurs during overfeeding, but the ability to maintain this hypophagia is substantially impaired in the absence of leptin signaling. In addition, this post-overfeeding leptin effect appears to occur despite the fact that leptin levels normalize relatively rapidly post-overfeeding.