A new study in rats suggests that just a few days of consuming a diet high in saturated fat may be enough to trigger memory problems and brain inflammation in older adults.

Researchers examined the effects of a high-fat diet on both young and old rats over two different time periods three days and three months to compare how quickly dietary changes impact the brain versus the body. As expected, long-term high-fat consumption (three months) resulted in metabolic issues, gut inflammation, and gut microbiome shifts in all rats. However, short-term exposure (three days) did not cause significant metabolic or gut changes.

Surprisingly, only older rats whether consuming the high-fat diet for three days or three months showed memory impairments and brain inflammation.

These findings challenge the idea that diet-related brain inflammation in aging is solely driven by obesity, explained senior author Ruth Barrientos, a researcher at the Institute for Behavioral Medicine Research at The Ohio State University. While many studies link processed and fatty foods to brain health through obesity, the direct effects of diet alone remain underexplored.

“Unhealthy diets and obesity are connected, but they don’t always go hand in hand. We wanted to isolate the diet’s direct impact on the brain,” said Barrientos, who is also an associate professor of psychiatry, behavioral health, and neuroscience at Ohio State’s College of Medicine. “Our study shows that within just three days long before obesity develops significant neuroinflammatory changes occur.”

The study, published in Immunity & Ageing, highlights how aging primes the brain for an inflammatory response, reducing its ability to recover and making an unhealthy diet even more harmful.

The high-fat diet used in the study derived 60% of its calories from fat, similar to common fast-food options, such as a McDonald’s double smoky BLT quarter pounder with cheese or a Burger King double whopper with cheese.

Memory assessments focused on two cognitive functions commonly affected in dementia contextual memory (linked to the hippocampus, the brain’s memory center) and cued-fear memory (associated with the amygdala, which processes fear and danger). Older rats on a high-fat diet for just three days showed impairments in both areas, and these deficits persisted throughout the three-month diet period.

Additionally, aged rats exhibited shifts in brain cytokine levels proteins that regulate inflammation after only three days on the high-fat diet, suggesting a dysregulated inflammatory response. After three months, cytokine levels remained abnormal, and cognitive deficits persisted.

“Deviations from baseline inflammatory markers are harmful and have been linked to impaired learning and memory,” Barrientos noted.

After three months, both young and old rats on the high-fat diet exhibited weight gain, insulin resistance, increased blood sugar, inflammatory proteins in fat tissue, and alterations in gut microbiota. However, only aged rats experienced memory deficits.

“Young rats appear more resilient, likely because they can activate compensatory anti-inflammatory responses that older rats lack,” Barrientos explained. “With both age groups showing metabolic changes, we can’t attribute memory impairment solely to obesity-related factors it’s the brain’s response that matters.”

This study, supported by the National Institute on Aging, underscores the importance of diet in cognitive health, particularly in aging populations.

Source: https://news.osu.edu/memory-is-impaired-in-aged-rats-after-3-days-of-high-fat-eating/