Adaptations of adult lean and obese zucker rats during food restriction

Abstract

The adaptations that occur during prolonged food restriction of adult lean and obese Zucker rats were examined. Lean Zucker rats were restricted until they lost 31% (RL-31) or 42% (RL-42) of their starting weight. Obese Zucker rats were restricted until they lost 53% (RO-53) or 78% (RO-78) of their initial weight. Weights of five skeletal muscles, three fat pads and two organs were determined. During restriction, the obese rats catabolized less muscle protein per day than the lean animals. The percentage of muscle lost by the obese was lower than the percentage body weight loss. After prolonged restriction, both lean and obese rats were essentially depleted of fat stores. Obese rats relied to a greater extent on fat stores for energy and to a lesser extent on catabolism of lean body mass than lean rats. The ratios of protein/DNA and RNA/DNA were significantly reduced in muscles from all restricted animals and the DNA content was lower in the groups that lost the most weight (RL-42 and RO-78). In conclusion, obese Zucker rats have an enhanced ability to adapt to restriction with a slower rate of skeletal muscle catabolism. However, “survival” during prolonged restriction is dependent on the initial amount of adipose tissue and not loss of a critical amount of lean body mass.