Effect of postweaning feed restriction on adipose cellularity and body compositon in polygenic obese mice

The M16 line of mice, selected for rapid postweaning gain, exhibits polygenically controlled obesity and hyperphagia. The effect of limiting postweaning energy intake on the subsequent growth and development of obesity in M16 mice was investigated. Male mice from M16 and an unselected line (ICR) were provided either ad libitum or limited (congruent to 70% of ad libitum) feed during the rapid postweaning growth period from 4 to 6 weeks of age. Body weights (g) at 6 weeks of age were: ad libitum ICR (31.0 +/- 0.6), restricted ICR (23.8 +/- 0.7), ad libitum M16 (45.0 +/- 0.6) and restricted M16 (30.1 +/- 0.6). In both lines, restricted feed intake severely depressed body fat, lean, ash, and water at 6 weeks. In addition, percent triacylglycerol, fat cell size and number in the epididymal fat pads were lower. Restricted M16 and ICR mice showed a marked compensatory gain in all body components when subsequently fed ad libitum for 10 weeks. All measurements of adiposity at 16 weeks were similar for the restricted and ad libitum regimens within each line. The relative amounts of energy deposited as fat and lean between 4 and 16 weeks were not influenced by restricted feeding, but M16 mice deposited a larger proportion of energy as fat than as lean when compared with ICR mice. The results suggest that fat cell number is determined at a relatively early age in mice and is primarily under genetic control.