Dietary self-selection in intact, ovariectomized, and estradiol-treated female rats

The effects of estrogenic stimulation on diet selection were examined in intact, estrous cycling rats, ovariectomized (OVX) rats, and OVX rats given estradiol benzoate (EB) hormone replacement therapy. In Experiment 1, OVX was associated with the nearly exclusive choice of the more calorically dense diet of a pair of diets varying in the concentration of one of the three basic macronutrients (i.e., fat, carbohydrate, and protein), an effect that was decreased by EB administration. In the second experiment, dietary self-selection was examined in intact, estrous cycling rats given access to an isocaloric diet triplet of fat, carbohydrate (CHO), and protein. Total caloric intake and body weight did not vary across the estrous cycle. However, diet selection did vary. Fat intake increased; CHO and, to a lesser extent, protein intake decreased during estrus. An opposite diet selection occurred during diestrus. In Experiment 3, OVX resulted in progressive increases in CHO and protein intake, with a concurrent decrease in fat consumption. The EB treatment partially reversed this diet selection profile (Experiment 4). These results were confirmed by diet pairs with both naturally occurring and experimentally produced estrogenic stimulation (Experiments 5 and 6). These data are consistent with the findings of previous research demonstrating estrogenic reduction in CHO intake with standard high-CHO commercial diets. In addition, an increase in fat intake during estrogenic stimulation was found.