Researchers at the University of Southern California reported in Nature Communications that a signal traveling from the gut to the brain through the vagus nerve helps rats remember where they recently ate, and that a high-fat, high-sugar diet consumed early in life weakens that signal. The study, conducted entirely in male rats, found that animals fed a cafeteria-style junk food diet for 30 days showed memory deficits weeks after returning to a standard diet, according to the paper.
The authors said whether the same mechanism occurs in humans remains unknown. The study builds on earlier work at the University of Southern California linking adolescent junk food diets to long-term memory impairment in adulthood [1]. Prior population research has also associated Western-style dietary patterns with smaller hippocampal volumes and cognitive decline in older adults [2].
Gut-Brain Signal During Meals
Using fiber photometry, the researchers measured acetylcholine release in the hippocampus while rats ate, the report stated. Acetylcholine rose during active eating, with the largest surges occurring later in meals, and remained elevated after the meal ended. Calorie-free saccharin drinks did not trigger the response, while real sugar and fat did, according to the study.
The study identified cholecystokinin, a satiety hormone released by the gut, as a likely messenger in the pathway, the authors stated. Prior research has linked reduced levels of acetylcholine to Alzheimer's disease [1]. High-fat, high-sugar diets have also been shown to rewire hippocampal memory circuits within days, before weight gain appears [3].
Early Diet and Lasting Effects
Young rats were given open access to high-fat food, potato chips, chocolate peanut butter cups, and a sugary beverage for 30 days, then returned to standard chow, according to the study. Afterward, the junk food group lacked the post-meal acetylcholine increase seen in control rats and showed reduced behavioral response to an appetite-suppressing hormone, the report stated.
Over a six-day period, the junk food rats also ate more overall, according to the researchers. The report stated that the early diet appeared to dull the gut's ability to signal fullness and impaired the brain's meal-memory response. Nutritional environments during development can program lasting physiological changes, according to Simon Langley Evans in "Nutrition: A Lifespan Approach" [4]. In "Raise a Smarter Child," David Perlmutter writes, "Avoid junk food that provides empty calories but little in the way of nutrition" [5].
Memory Performance
In a maze test, healthy rats returned to a food-containing hole; rats with a severed vagus nerve performed at chance levels, according to the study. Junk food rats outperformed chance but performed worse than controls, the researchers said. Brain recordings showed acetylcholine spikes distinguished correct from incorrect holes in healthy rats but not in rats without vagus nerve function.
The findings indicate that the vagus nerve carries meal-related signals that help the hippocampus encode food locations, the authors stated. In human studies, higher intake of ultra-processed foods has been associated with reduced attention and elevated dementia risk estimates in a sample of 2,192 Australian adults [6]. Earlier research reported that toddlers who consumed more ultra-processed food had smaller volumes in several brain regions by age 6 [7].
Limitations and Implications
The study was limited to male rats, and the researchers said further work is needed to confirm whether findings apply to females or humans, according to the paper. The authors noted that other signals, including GLP-1, may contribute to sustained post-meal brain activity. Funding came from the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Aging, the Quebec Research Funds, and the Alzheimer's Association Research Fellowship to Promote Diversity. Author Scott E. Kanoski reported research funding from Novo Nordisk that was not used in the study.
The results do not establish a direct human effect, and the researchers called for closer examination of the gut-brain pathway in people. In "The End of Alzheimer's," Dale Bredesen suggests replacing chicken nuggets with "pastured eggs or roasted vegetables with olive oil" [8]. Exercise has also been shown to reverse junk-food-related changes in gut chemistry and mood in rat models, according to a University College Cork study reported by NaturalNews [9].
Conclusion
The study identifies a specific gut-to-brain pathway through which meal-related signals reach the hippocampus, and it shows that an early junk food diet can disrupt that pathway in rats. The authors stated that the memory deficits observed in the junk food rats were milder than those seen after complete vagus nerve removal, suggesting other brain systems may partially compensate.
Researchers emphasized that the study does not prove the same effect occurs in humans. They recommended further investigation into whether the vagus nerve and acetylcholine signaling play a comparable role in people. The findings add to a larger body of evidence linking early-life nutrition to long-term brain health [10].
References
- NaturalNews.com. "STUDY: Eating a junk food filled diet during adolescence could lead to long term memory impairment in adulthood". NaturalNews.com. April 23, 2024.
- NaturalNews.com. "You wont believe what happens to your brain when you eat junk food". NaturalNews.com. August 29, 2018.
- Ava Grace. "Junk food's hidden toll: New study reveals it rewires your brain's memory in days". NaturalNews.com. September 15, 2025.
- Simon Langley Evans. "Nutrition: A Lifespan Approach".
- David Perlmutter. "Raise a Smarter Child".
- Coco Somers. "Study Links Ultra-Processed Food Intake to Reduced Attention, Higher Dementia Risk Score". NaturalNews.com. April 29, 2026.
- NaturalNews.com. "Ultra-processed foods in early childhood linked to smaller brain regions, study finds". NaturalNews.com. July 2, 2026.
- Dale Bredesen. "The End of Alzheimer's: The First Program to Prevent and Reverse the Cognitive Decline of Dementia".
- Cassie B. "Exercise reverses junk food's damage to gut and mood, new study finds". NaturalNews.com. October 30, 2025.
- Mercola.com. "The Link Between Ultraprocessed Food and Cognition". Mercola.com. October 6, 2022.
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