Dietary fat dose dependently increases spontaneous caloric intake in rat

Objective: To characterize the dose-response relationship between dietary fat to carbohydrate ratio and spontaneous caloric intake. Research Methods and Procedures: Male Long-Evans rats consumed milk-based liquid diets that differed in fat content (17% to 60% of kilocalories) but had equivalent protein content and energy density. In Experiment 1, rats consumed one of the diets (n = 9/diet group) as the sole source of nutrition for 16 days. In Experiment 2, diets were offered as an option to nutritionally complete chow for 4 days followed by a 3-day chow-only washout in a randomized within-subjects design (n = 30). In Experiment 3, nine rats received isocaloric intragastric infusions of diet overnight, with chow available ad libitum. At least two no-infusion days separated the different diet infusions, which were given in random order. Food intake was measured daily Results: Dietary fat dose dependently increased total daily kilocalories in each of the three paradigms. Discussion: These data imply that the postingestive effects of carbohydrate and fat differentially engage the physiological substrates that regulate daily caloric intake. These findings reiterate the importance of investigating macronutrient-specific controls of feeding, rather than prematurely concluding that dietary attributes that covary with fat content (e.g., caloric density and palatability) drive the overeating associated with a high-fat diet.