Maintenance on an energy‐dense “cafeteria diet” reduces the reinforcing effectiveness of corn oil but not saccharin in rats

Abstract

Rats made obese on energy‐dense diets show alterations in brain reward function that include decreased sensitivity to brain stimulation reward and decreased psychostimulant self‐administration. However, it is currently unclear how diet‐induced obesity affects the reinforcing effects of fat and sweet taste. The current study used behavioral economics (BE) and progressive‐ratio (PR) tests to determine if maintenance on a palatable, energy‐dense “cafeteria diet” (CD) alters fat and sweet taste reinforcement. In addition to ad lib chow, a CD consisting of high‐fat, high‐sugar snack foods was made available for 18‐h (extended access [EA]) or 1‐h (restricted access) per day throughout the experiment in two groups of rats. A third group received ad lib chow only (CO). After 40 days of CD treatment, the EA rats were approximately 100 g heavier than the other groups. The reinforcing effectiveness of corn oil and saccharin were then tested in a BE design and subsequently in a PR design. Both tests revealed that corn oil was a more effective reinforcer than saccharin in CO rats, and a more effective reinforcer in CO rats than in EA rats. There were no other differences within or between groups in either test. These results indicate that maintenance on a palatable, energy‐dense diet and/or obesity reduces the reinforcing effectiveness of a fat in the form of corn oil but does not affect the reinforcing effectiveness of sweet taste.