Western-style diet and its impacts on hippocampal-dependent processes

Based mainly on animal data it has been argued that a Western-style diet impairs hippocampal functions involved in regulating ingestive behaviour – including hippocampal-dependent learning and memory (HDLM), sensitivity to interoceptive signals of hunger and satiety, and the use of such signals to inhibit eating. This thesis has three specific aims, all of which examine whether dietary-induced impairments in animals are evident in humans: (1) To determine if greater consumption of saturated fats and refined sugars (HFS) prevalent in a Western-style diet is associated with impaired hippocampal inhibitory processes for ingestive behaviour; (2) To review any published causal evidence that manipulating energy intake and macronutrient content impacts cognitive function; and (3) To empirically test if an HFS diet causes impairments in hippocampal functions related to ingestive behaviour. Study 1 used a correlational design revealing that greater intake of an HFS diet was associated with poorer HDLM, poorer ability to inhibit wanting (relative to liking) of palatable foods based on physiological state, with the latter being hippocampally-mediated. Study 2 was a systematic review of human experimental studies, revealing that long-term verbal memory tasks were most impacted by changes in energy and fats. Study 3 used an experimental design to show that lean individuals given an HFS diet-intervention for 4 days revealed poorer HDLM and ingestive interoception, relative to a control group. Additionally, greater HDLM impairment was related to larger changes in blood glucose, suggesting one potential pathway by which diet affects the brain. Overall, these findings are consistent with those from animals, providing novel translational findings and the first causal evidence that an HFS diet impairs HDLM