EFFECT OF AGE ON PROTEIN CONSERVATION DURING VERY-LOW-ENERGY DIET IN OBESE SPRAGUE-DAWLEY RATS

Objective: To examine the effect of age on body protein losses occurri ng during severe energy restriction in obesity. Research Methods and P rocedures: Weanling (young) Sprague-Dawley rats (YR) were fed a high f at (35% energy) diet (HED) until mean body weight approached that of a group of chow-fed retired breeder (aged) rats (AR). Both groups were then fed HFD for an additional 2 weeks, after which selected controls from YR and AR groups were killed for baseline carcass analysis. Remai ning rats were fed a very-low-energy diet (VLED, 33% kcal of HFD) for 3 weeks and then killed for carcass analysis. Results: YR had greater fat stores before VLED, and lost proportionately more fat and less pro tein during VLED than did AR. Weight loss composition during VLED was 66.7% fat, 11.1% protein, and 22.2% water in YR, and 39.4% fat, 26.2% protein, and 34.3% water in AR. Greater YR fat loss during VLED (70.6 +/- 30.4 vs. 32.6 +/- 29.1 g in AR; mean +/- SD) was paralleled by sig nificantly larger decreases in epididymal and retroperitoneal fat pad weights, mean adipocyte size, and lipoprotein lipase activity. Greater protein loss in AR (21.6 +/- 13.9 g vs. 11.8 +/- 10.7 g in YR) coinci ded with larger decreases in visceral organ weights and serum thyroxin e and triiodothyronine. Energy expenditure changes during VLED were si milar between groups. Discussion: Dietary obese young rats appear bett er able than aged rats to conserve body protein while losing body fat during severe energy restriction.