Pattern of dietary self-selection in VMH-lesioned rats

Abstract

Adult female rats were given ad lib access to either a self-selection regime with separate sources of the three macronutrients, protein, fat and carbohydrate, or a single nutritionally complete diet. Following 28 days of baseline measurements, animals in each dietary condition were chosen to receive either bilateral lesions of the ventromedial area of the hypothalamus (VMH) or sham-operations. Selecting animals were maintained on the self-selection regime throughout the post-operative period. Animals in the single diet condition continued to receive their pre-operative diet, ground Purina Chow, for the first 21 days following surgery and then were switched to a high-fat diet. During the pre-operative period, selecting animals chose a daily average of 29.4% of their calories as protein, 44.3% as carbohydrate and 26.3% as fat. Although selecting animals did not increase caloric intake following VMH damage, they did modify patterns of diet selection. After destruction of the VMH, selecting animals significantly increased both absolute and percent fat intake, and decreased both absolute and percent protein intake. Although absolute carbohydrate intake did not vary, percent carbohydrate intake did decrease significantly as a function of VMH lesions. No significant modifications in caloric intake or diet selection were observed in sham-operated animals. In comparison to sham-operated animas, lesioned animals in both dietary conditions displayed increased rates of food utilization, calculated as grams of body weight gained per 100 kcals consumed. Additionally, lesioned animals in both dietary groups drank significantly less water than sham-operated animals.