Caloric regulation and patterns of food choice in a patchy environment: the value and cost of alternative foods.

Rats in a laboratory foraging paradigm had 24-hr-per-day access to a feeder where they could search, by completing a fixed number of bar presses, for an opportunity to eat one of a pair of foods differing in caloric density (2.5, 3, 3.5, or 4 kcal/g) and, in Experiment 2, the price of food pellets (10 to 50 bar presses per pellet). The rats could either accept the opportunity, and eat a meal, or reject it in favor of further search. Daily caloric intake was relatively constant. The rats always included both foods in their diet, but, for any particular food, the degree of inclusion in the diet and of acceptance of meal opportunities, the meal size, and the rate of eating were all functions not only of the price and caloric value of that food but also of the price and value of the alternately-available food. The patterns of intake for one food relative to those for the other available food were strongly correlated with the relative rate of calorie intake during consumption of that food compared to the other. Although the rats appeared to be sensitive to the local rates of calorie flow, they did not maximize daily calories consumed per time spent feeding.