Just a few days of eating a diet high in saturated fat could be enough to cause memory problems and brain inflammation in older adults, according to a new study in rats.
Researchers from The Ohio State University compared how quickly diet-related changes occur in the brain and body when rats are fed a high-fat diet.
Young and old rats were fed either for three days or for three months, allowing scientists to assess the short- and long-term effects.
After three months, both young and old rats developed metabolic issues, gut inflammation, and shifts in gut bacteria—typical results of long-term unhealthy eating.
However, just three days of eating fatty food did not cause major changes in the body.
But the brain told a different story. Only older rats, regardless of whether they ate high-fat food for three days or three months, showed memory issues and signs of inflammation in the brain.
This suggests that aging brains are more vulnerable to the effects of unhealthy diets—and that damage can start quickly, even before any signs of obesity appear.
“Unhealthy diets and obesity are linked, but they are not inseparable,” said lead researcher Ruth Barrientos. “We showed that within three days, long before obesity sets in, tremendous neuroinflammatory shifts are occurring.”
Barrientos’ team tested two types of memory in rats: one involving the hippocampus (responsible for general memory) and another involving the amygdala (linked to fear memory). Older rats on the high-fat diet showed impairment in both types of memory after just three days, and the issues continued after three months.
The study also found increases in inflammatory proteins called cytokines in the brains of older rats, indicating an overactive immune response. While younger rats also gained weight and showed body inflammation after three months on the same diet, their brains and memory functions remained intact.
The high-fat diet used in the study contained 60% of its calories from fat, similar to many fast-food items. For instance, McDonald’s Double Smoky BLT Quarter Pounder with Cheese and Burger King’s Double Whopper with Cheese fall in that range.
Barrientos emphasized that the study reveals how damaging even a few days of fatty eating can be for aging brains, independent of body weight or obesity. “It’s what is happening in the brain that’s important for the memory response,” she said.
The research, published in the journal Immunity & Ageing, was supported by grants from the National Institute on Aging.
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