Effect of prolonged experimental protein malnutrition and of refeeding on growth, adipose tissue development and body composition in rats

The effect of experimental protein malnutrition and of subsequent refeeding at various ages on growth, adipose tissue development, body composition and serum triiodothyronine (T3) concentration were studied in weanling, male Sprague-Dawley rats fed isoenergetic diets containing 22% casein (controls) or 8% casein (PM-3) from 3 until 33 weeks of age. In addition, groups of control rats were switched to the 8% casein diet at 7 weeks of age (PM-7), and groups of PM-3 rats were refed the control diet from 7 (RF-7) or 11 (RF-11) weeks of age. At 33 weeks of age, PM-3 rats were 56% and PM-7 rats 82% the weight of controls, while RF-7 rats were 84% and RF-11 77% the weight of controls, respectively. Carcass fat and energy content corresponded to body weight in all groups. The weights of the epididymal fat pads of control rats did not increase after 24 weeks of age. The epididymal fat pad weights of all other groups remained smaller than those of controls, but continued to increase throughout the study. Epididymal adipocyte numbers did not change after 11 weeks of age in control rats or after 17 weeks of age in PM-7 and RF-7 rats, but continued to increase throughout the 33 weeks in the PM-3 and RF-11 rats. Adipocyte size increased with age in all groups but remained smaller throughout in PM-3 rats. Serum T3 concentrations were greatest in the PM-3 rats, intermediate in the PM-7 rats and became normalized in both RF groups by 33 weeks of age. These studies confirm that the postweaning protein deprivation impairs the growth of lean tissues and indicate that its primary effect on adipose tissue is a decrease in adipocyte proliferation and/or differentiation which may not recover with refeeding.