High-fat diets impair conditional discrimination learning in rats

At the age of 1 month, four separate groups of Long-Evans rats were placed on diets varying in the amount and composition of dietary fat. High-saturated-fat diets (lard based) were either 20% or 10% (w/w) of the diet. High-polyunsaturated-fat diets (soybean oil based) were either 20% or 5% (w/w) of the diet. A fifth group of rats consumed standard laboratory chow (4.5% w/w fat). After 3 months, all the rats were tested on a conditional discrimination learning task in which they were required to associate different stimuli with different responses. Independent of the source of dietary fat, the animals fed high-fat diets (20% w/w) were impaired on the task. Performance of the animals fed the 10% lard diet was indistinguishable from that of the animals fed the 20% fat diets. In contrast, the rats fed 5% soybean oil (SBO) or chow diets displayed superior performance in comparison with all other groups. These data demonstrate that high-fat diets can have adverse effects on learning and memory and provide suggestive evidence that saturated fatty acids may be associated with the adverse effect.