Consumption of diets rich in refined sugar and saturated fat has been linked with development of mild cognitive impairment and dementia in humans. Most cognitive paradigms used in biomedical research to investigate the relationship between obesity and cognition rely on food motivation and speed of completion of a task, both of which can be influenced by the physiological changes induced by obesity. Here we assess the effects of an energy rich diet (Cafeteria Diet, CAF) on the performance of male Sprague-Dawley rats in the Decision Making paradigm, an operant conditioning task using water as a reinforcer and based on the patch depletion paradigm of optimal foraging in a test that is independent from motivation and time budget. As expected, CAF diet resulted in increased body weight and circulating leptin and insulin levels. Our results show that the decision rule of rats fed a CAF is altered at one month after diet initiation. In absence of insulin resistance and dyslipidemia, these results show that the CAF influences the cognitive performance of male rats in the DM prior to signs of developing metabolic syndrome.