Learned aversions to proteins in rats on a dietary self-selection regimen

Rats were allowed continuous access to protein and carbohydrate macronutrient sources during a sequence of cyclophosphamide (Cytoxan) injections. Significant aversions developed to the protein but not the carbohydrate source in three studies in which the composition of both protein and carbohydrate diets was varied. These results suggest that animals on a dietary self-selection regimen are more likely to develop conditioned aversions to the protein source than the carbohydrate source. In a final study, the generality of these findings was examined by determining whether aversions would selectively arise to protein but not carbohydrate when these nutrients were conditioned in a single trial, with a meal-feeding paradigm. Proteins again proved more salient targets for aversions than carbohydrates. These findings suggest that the tendency to associate proteins with drug-induced illness more readily than carbohydrates is not limited to a self-selection regimen. The possible role of taste factors and/or postingestive effects as the basis of the differential conditioning of proteins and carbohydrates is discussed.