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New research links a typical Western diet to lasting memory issues. Cavan Images/Getty Images
  • A new study in rats has found that a high-sugar, high fat diet, such as junk food or a Western diet, caused long lasting memory issues.
  • These foods are thought to disrupt the functioning of the hippocampus, an area critical for memory in humans as well as rats.
  • The most concerning finding may be that this damage to memory remained even after the rats were switched over to a healthy diet.

During childhood and adolescence, the human brain is especially vulnerable as it develops toward adulthood.

A new study of rats by researchers at USC Dornsrife in California finds that brains at this stage are especially susceptible to damage caused by high fat, high-sugar junk food — or a typical Western — diet.

The authors of the study investigated the effect of such foods on levels of the neurotransmitter acetylcholine (ACh), which is important for memory, including learning, arousal, and attention. Low levels of ACh have been linked to the development of Alzheimer’s disease in humans.

For the study, juvenile and adolescent rats were provided an assortment of foods. These included high-fat, high-sugar chow, potato chips, peanut butter cups, and high-fructose corn syrup, any one of which they could consume as desired. They also had ad libitum access to water.

Only standard chow and water were available to a control group of rats.

Upon achieving young adulthood, the rats were administered memory tests. Introduced to novel locations, each rat encountered new objects. After some days, the rats were reintroduced to these areas, with one new object having been added. Although the control group exhibited curiosity regarding that object, the experimental group appeared not to notice anything had changed.

Even after being switched to a healthy diet in adulthood, the experimental groups’ memory deficiencies persisted, suggesting potentially long-lasting damage to the brain.

The researchers observed compromised ACh signaling in the experimental groups’ hippocampus, a region closely associated with memory and learning in both rats and humans.

The study is published in Brain, Behavior, and Immunity.

It was in the hippocampus that the new study’s authors observed disrupted ACh signaling. The study’s senior investigator, Scott Kanoski, PhD, MS, professor of biological sciences at USC Dornsrife, explained to Medical News Today:

“The hippocampus is a brain region that is particularly susceptible to various environmental and biological insults. This is particularly true during the juvenile and adolescent periods when this brain region is still developing.”

“Our diet model produced acetylcholine disruption in the hippocampus in the rats analogous to disruptions observed in Alzheimer’s disease. However, more work is needed to understand how early life dietary and metabolic factors influence long-term risk for Alzheimer’s and other related dementias,” Kanoski continued.

Amy Reichelt, PhD, BSc with honors in Psychology, who was not involved in this study, has extensively studied the effect of foods on the developing brain.

“It would have been interesting if the authors also studied the effects of diet on acetylcholine signaling in the prefrontal cortex in adult and adolescent rats,” Reichelt said.

“This area of the brain is rich in ACh receptors, and also is the last part of the brain to mature, so changes may have been specific to the younger animals,” she added.

Reichelt reported that “research with rodents has shown that the prefrontal cortex [i]s vulnerable to the deleterious effects of poor diets that are high in fat and sugar. This is a key area of the brain for executive-control functions like decision-making and impulse control.”

“In particular, exposure to unhealthy diets has a more detrimental effect on cognition in adolescent animals.”
— Amy Reichelt, PhD

Reichelt said humans are among those animals, adding, “Brand new research conducted at SickKids also shows that the brains of children and adolescents with a higher BMI had different neuronal activity signatures associated with reductions in inhibition in the frontal cortex, reflecting a similar cellular profile to rats that ate a Western-style diet.”

The research Reichelt mentioned has yet to be published in a peer-reviewed journal and is a pre-print.

“In humans, longitudinal studies have shown that midlife dietary and metabolic factors (e.g., high fat diet, obesity) can increase risk for developing dementia later in life. However, the potential link with early life development is poorly understood,” Kanoski said.

It may not be that memory issues are permanent — further research is required. Still, Kanoski noted that even after being switched to a healthy adult diet, the rats’ memory did not improve.

“It is certainly possible that with a longer period on the healthy diet, these systems would have returned to normal. Future studies are needed to understand the parameters through which these long-lasting deficits can be reversed,” he said.

Improved memory with 2 drugs

The researchers did find, in another phase of their research, that the administration of two drugs — PNU-282987 and carbachol — directly into the hippocampus restored the rats’ memory.

In addition, the study reports that undesirable gut microbiome changes caused by a Western or junk diet can be reversed with a healthy diet. This may also have ramifications for memory.

“The inclusion of microbiome analysis in young animals is interesting because the microbiota has been shown to communicate with the brain through secretion of neuroactive chemicals,” said Reichelt.

Reichelt described the hazardous potential of the ultra-processed, high in fat and sugar nature of the Western diet.

“Research has shown that the high sugar aspect is particularly detrimental to memory function, causing a reduction in hippocampal neurogenesis — the development of new neurons in a key area of the brain required to form memories,” Reichelt said.

By way of example, Reichelt offered:

“In particular, when you consume high sugar drinks, like Coca-Cola, the sugar is rapidly absorbed from your gut into the blood where it causes a glucose spike. This then requires insulin to uptake the glucose into cells. Over-consumption of sugar-sweetened drinks can eventually lead to a blunting of insulin’s effectiveness, leading to metabolic syndrome and type 2 diabetes.”

Michelle Routhenstein, MS, RD, CDCES, preventive cardiology dietitian at EntirelyNourished.com, who was also not involved in the study, noted, “Diets high in saturated fat, refined sugar and processed carbohydrates have been linked to long-term cognitive decline.”

“These [junk] foods, in excess can promote inflammation, oxidative stress, plaque in the arteries and increase in blood sugar levels which can impede on vascular health leading to potential long term cognitive damage, including vascular dementia.”
— Michelle Routhenstein, MS, RD, CDCES

For Reichelt, the ideal memory food is clear: “Eggs! Eggs (particularly the yolk) are an excellent source of choline, which is a building block of acetylcholine.”

In addition to eggs, Routhenstein suggested some “foods that may help to promote healthy acetylcholine signaling include foods rich in choline, such as fish — specifically omega-3 rich varieties found in salmon, sardines, and arctic char — nuts, and cruciferous vegetables like broccoli, cabbage, and Brussels sprouts.”