Intact regulation of protein intake during the development of hypothalamic or genetic obesity in rats

Adult female rats made hyperphagic with bilateral lesions of the medial hypothalamus as well as spontaneously hyperphagic adult female rats of the Zucker strain were studied for their abilities to regulate dietary protein and energy intakes. This was accomplished by permitting both models of animal obesity to select freely between two isocaloric diets containing 10% vs 60% by weight casein (protein) for at least one month. Compared to appropriate control groups, both experimental groups became obese by consuming more of the low protein diet and less of the high protein diet. The overall effect of this selection pattern was an excessive intake of energy in the form of carbohydrate and fat while maintaining control levels of protein intake. These data imply that the stimulus for hyperphagia in both animal models of obesity is some physiological and/or behavioral error in energy regulation but not protein regulation.