SUBSTITUTION AND CALORIC REGULATION IN A CLOSED ECONOMY

Three experiments were conducted to study the effect of an imperfect s ubstitute for food on demand for food in a closed economy. In Experime nts 1 and 2, rats pressed a lever for their entire daily food ration, and a fixed ratio of presses was required for each food pellet. In bot h experiments, the fixed ratio was held constant during a daily sessio n but was increased between sessions. The fixed ratio was increased ov er a series of daily sessions once in the absence of concurrently avai lable sucrose and again when sucrose pellets were freely available. Fo r both series, increases in the fixed ratio reduced food intake, but b ody weight was reduced only in the no-sucrose condition. In the sucros e condition, body weight and total caloric intake (sucrose plus food) were relatively unaffected by increases in the fixed ratio. At all fix ed ratios, food intake was proportionally reduced by the intake of suc rose. In Experiment 3, monkeys obtained food or saccharin by pressing keys; the fixed ratio of presses per food pellet was increased once wh en tap water was each monkey's only source of fluid, again when each m onkey's water was sweetened with saccharin, and a third time when each monkey had concurrent access to the saccharin solution and plain wate r. Increases in the fixed ratio, but not the intake of the saccharin s olution, reduced each monkey's food intake. Because neither rats' sucr ose nor monkeys' saccharin intakes affected the slope of the respectiv e demand curves for food, monkeys and rats increased their daily outpu t of presses and thereby defended their daily intake of those compleme ntary elements of food. However, sucrose reduced rats' food intake. Th e relative constancy of body weight and total caloric intake in the su crose condition is consistent with the possibility that rats tended to regulate caloric intake.