Researchers identify how eating a Western diet impairs memory functioning

In a recent study, researchers have shed light on how early consumption of a Western diet — characterized by high levels of processed foods, saturated fats, and simple sugars — can lead to lasting deficits in hippocampal-dependent episodic memory, despite not causing obesity or metabolic dysfunction.

This research emphasizes the critical role that diet plays in brain health, particularly during early developmental stages, and points towards acetylcholine signaling in the hippocampus as a potential mediator of these long-lasting memory impairments. The findings have been published in Brain, Behavior, and Immunity.

Previous research has found a connection between the consumption of a Western diet and various cognitive issues. However, what remained elusive was the mechanisms that could explain how these dietary habits lead to specific cognitive detriments, such as memory loss. The new study was motivated by the broader goal of contributing actionable insights into public health strategies aimed at preventing cognitive decline.

“In addition to promoting obesity and metabolic dysfunction, a diet high in saturated fat, added sugars, and processed foods can lead to memory impairments. We were interested in understanding the underlying neurobiological mechanisms for this connection,” said study author Scott E. Kanoski, a professor of human and evolutionary biology at the University of Southern California.

To explore the long-term effects of an early life Western diet on cognitive functions, the researchers turned to male Sprague Dawley rats, which were chosen for their well-documented responses in dietary and cognitive research.

The study commenced when the rats were on postnatal day 25, a critical period for development. The dietary regimen was designed to closely mimic the nutritional profile of a Western diet, characterized by high fat, high sugar, and processed foods. To achieve this, the researchers used a cafeteria-style diet model, providing rats with free-choice access to various high-fat, high-sugar foods, and drinks, alongside standard chow for control animals.

The researchers found that rats fed a Western diet during early development exhibited significant, long-lasting deficits in hippocampal-dependent episodic memory, which disruptions in hippocampal acetylcholine signaling acting as a potential mediator.

Acetylcholine is a critical neurotransmitter for learning and memory processes, and its disruption has been linked to cognitive decline and conditions like Alzheimer’s disease. In the Western diet-fed rats, there were notable changes in acetylcholine neurotransmission within the hippocampus, including altered dynamics of acetylcholine release during memory tasks and long-term reductions in cholinergic tone.

These findings point to a significant role of acetylcholine signaling in the observed cognitive deficits, suggesting that dietary influences on this neurotransmitter system could underlie the lasting memory impairments.

The researchers also explored the role of the gut microbiome in mediating the cognitive effects of a Western diet. While early life consumption of this diet altered the gut microbiome, these changes were largely reversible with a subsequent healthy diet intervention. This reversibility of microbiome alterations, however, did not extend to the cognitive impairments, which persisted despite the dietary switch.

The findings indicate that “what types of food one consumes can have impacts on brain function throughout the lifespan, but particularly during early life periods when brain systems are still developing,” Kanoski told PsyPost. However, he noted that “these results come from rodents. While rodents are a good model for human physiology and metabolic function, more research is needed with regards to translational relevance.”

The study, “Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signaling,” was authored by Anna M.R. Hayes, Logan Tierno Lauer, Alicia E. Kao, Shan Sun, Molly E. Klug, Linda Tsan, Jessica J. Rea, Keshav S. Subramanian, Cindy Gu, Natalie Tanios, Arun Ahuja, Kristen N. Donohue, Léa Décarie-Spain, Anthony A. Fodor, and Scott E. Kanoski.