Date of Thesis


Thesis Type

Honors Thesis

Degree Type

Bachelor of Science

First Advisor

Kevin Myers


Animals use classical conditioning to learn predictive relationships between flavors and postingestive nutrients, which allows them to regulate their body weights. This is made difficult by modern diets, which have confusing flavor-nutrient relationships due to added fats, sugars, and flavors in processed foods. Cafeteria diets containing a variety of human-typical foods are often used to study the effects of a modern diet in animal models. Foods used in cafeteria diets typically combine aspects such as high-fat high-sugar, variety, and high palatability. However, no past studies have analyzed the effect of variety on flavor-nutrient learning by using only natural foods. In the current study, 36 rats were assigned to three dietary conditions: a processed foods (PF) cafeteria diet, natural foods (NF) cafeteria diet, or chow-only control (CON) diet. After three months on the diets, rats were tested on their ability to learn about new foods and on their response to sweet taste. The rats were first tested with flavor-nutrient conditioning (FNC) to analyze the degree to which they were capable of learning new flavor-nutrient relationships. Several measures of FNC revealed that PF rats were not impaired in learning, and were perhaps better able to discriminate between flavors than NF or CON rats. Throughout the present studies, rats in the cafeteria diet groups were found to consistently consume less sweet-tasting solutions than CON rats in ad libitum intake tests. To determine the cause of this difference in sweet intake, rats' motivation and hedonic liking for sucrose was analyzed by using a progressive ratio lever-pressing task for sucrose reward as well as lick microstructure analysis. Results indicated that rats were all equally motivated to work for sucrose, but that NF rats perceived high concentrations of sucrose as much more palatable than PR and CON rats. This study demonstrates that processed and natural foods cafeteria diets do not impair new flavor-nutrient learning, but they do cause rats to reduce sugar intake, for which the reason is still unknown.