Sucrose-induced obesity impairs novel object recognition learning in young rats

In addition to its metabolic consequences, obesity may lead to impairments in learning and memory. To test this possibility, male Long-Evans rats were fed ground chow, or chow and either a 32% sucrose solution or hydrogenated vegetable fat (Crisco) for eight weeks. Cognitive behavior was then assessed using a novel object recognition task. To determine if there was a relationship between cognitive behavior and glucose metabolism, performance on the novel object recognition task was correlated with fasting blood glucose levels and responses on an oral glucose tolerance test. Rats fed sucrose or fat consumed more calories, gained more weight, and had larger epididymal fat pads than rats fed only chow. Additionally, fasting blood glucose levels, and the area under the glucose curve following an oral glucose tolerance test were greater in rats consuming a supplemental source of fat or sucrose than in those eating only chow. During training when rats were presented with two identical objects in an open field, time spent exploring the objects did not differ as a function of dietary conditions. However, when rats were tested 1 h later with one familiar and one novel object, rats given sucrose spent significantly less time exploring the novel object than rats eating only chow. The percent of time spent exploring the novel object was negatively correlated with fasting blood glucose levels, final body weights, and epididymal fat pad weights. It is hypothesized that the impairment in object recognition in rats eating sucrose is due, at least in part, to diet-induced alterations in glucose metabolism.