Muscle catabolism in lean and obese zucker rats fed a very low calorie diet

In this study we examined the adaptations of adult lean and obese Zucker rats to a very low calorie diet (VLCD) or simple starvation. Lean rats were fed the VLCD or starved until they lost 31% of their starting weight. Obese rats were subjected to the same two treatments until they had lost about 52% of their initial weight. Weights of five skeletal muscles, three fat pads, and three organs were determined. Compared to the lean rats, obese rats relied to a greater extent on catabolism of fat stores for energy and to a lesser extent on lean body mass during both types of food restriction. Obese rats on the VLCD lost significantly less skeletal muscle, but not cardiac muscle, than the starved rats. Both the VLCD and starved groups experienced a 27-28% loss of cardiac muscle mass. This "protein-sparing" effect of the VLCD was seen in both the tissue weights and protein contents of skeletal muscle. Lean rats were not as capable of minimizing muscle losses during the rapid body weight loss due to the VLCD. In conclusion, obese Zucker rats have an enhanced ability to conserve skeletal muscle when fed a VLCD, but cardiac muscle is not "spared" in the same manner as skeletal muscle.