Macronutrient choice following food deprivation: effect of dietary fat dilution

Under standard laboratory conditions rats given access to three separate macronutrient sources compose a diet yielding 31% of their total daily calories as protein, 34% as carbohydrate, and 34% as fat. This selection pattern is dramatically altered with restored access following a 48 h fast. During the first hour of refeeding, rats composed a diet that was low in protein and high in carbohydrates and fat. By the end of 24 h, no difference in selection pattern was found, though intake of all three macronutrients was higher than baseline. A separate group given access to three macronutrient sources of equal caloric density specifically increased fat intake during the period of restored access. Another group, familiarized with a concentrated fat source, was given access to a diluted fat source during refeeding. Similarly, a fourth group, familiarized with a diluted fat source during the baseline condition was given access to a concentrated fat source during refeeding. Results from these experiments suggest that prior experience with a diluted fat source promotes a significant increase in fat intake and a suppression of carbohydrate intake during initial refeeding following a 48 h fast. In a second experiment, rats that were given a choice of both fat sources preferred the concentrated source; 72% of all fat (g) and 82% of all fat calories were consumed from the concentrated fat source. These results suggest that fat intake increases following deprivation not solely due to its inherent relatively increased caloric density but also possibly due to its role in energy metabolism.