Neural mechanisms linking Western diet consumption and cognitive impairment: a role for the vagus nerve

Consumption of a Western diet containing large proportions of calories from highly palatable foods that are high in fat and sugar is causally linked with obesity and metabolic dysfunction. In addition to these widely known deficits, Western diet consumption also negatively impacts various cognitive domains, including learning and memory function (e.g. Alzheimer's and related dementias), affective processes (e.g. anxiety, depression), and reward-related behaviors. However, the underlying neurobiological mechanisms that link Western diets to impaired cognition are poorly understood. In this review, we highlight recent findings revealing the impacts of Western diet consumption on the molecular machinery and signaling of key central neuromodulators (acetylcholine, dopamine, serotonin) that contribute to the dysregulation of fundamental cognitive and behavioral processes. Based on emerging evidence, we propose that Western diet-associated perturbations in central neuromodulator signaling and associated neurocognitive impairments are driven, at least in part, by blunted gut-to-brain communication through the vagus nerve. While future research is necessary to fully elucidate this hypothesized connection, it provides a framework to advance our understanding of the mechanisms mediating diet-cognition interactions.