Dementia and learning impairment are associated with increasing age, and age-related diseases such as Alzheimer’s disease. There is evidence to suggest age-related cognitive decline is also associated with increased metabolic stress and disturbances in insulin signaling. Diets high in animal fat and table sugar are metabolically stressful, especially with increasing age, and place greater demands on mitochondrial bioenergetic machinery. This study was designed to show that a metabolically stressful diet would increase the severity of cognitive dysfunction in aging mice. Ten C57BL/6 male mice were fed a high fat and sugar (HFS) diet starting at 21 months of age. The diet consisted of 15% protein (casein), 58% fat (lard), and 27% carbohydrates (sucrose), as well as a vitamin and mineral mix. Nine mice were fed regular rodent chow (RC) diet, consisting of 24.5% protein (balanced amino acid mix), 13.1% fat (soy bean oil), 62.4% carbohydrates (28.2% starch and 3.25% sucrose), and a vitamin and mineral mix, for the same time period. Mice were weighed weekly and assessed for body fat using quantitative magnetic resonance imaging. After 7 weeks, mice were tested for learning impairment using a box maze paradigm. Mice on the HFS diet gained an average of 9.62 grams of body weight, with an average 18.7% increase in fat mass compared to mice on the RC diet. Mice on the RC diet showed moderate levels of learning impairment. Surprisingly, mice on the HFS diet showed very little learning impairment, suggesting that some component in the HFS diet had a sparing effect on cognitive decline. This observation may be unique to mice, and certainly requires additional studies, but still raises an intriguing implication for how clinicians and dieticians might consider alternative intervention strategies for cognitively impaired individuals.