Study links processed foods lacking fiber to cognitive decline in aged brains

A study has found that the emotional memory region of the brain, the amygdala, is sensitive to processed foods. The study links the finding mainly to the diet’s lack of fiber, which leads to a decline in gut-derived butyrate metabolites and may cause inflammation in the brain. 

The brain region governs emotional memories, especially bad experiences, and is important for learning associations between something fearful and a bad outcome, the researchers argue.

Western processed foods, often high in saturated fats and refined carbohydrates, have previously been linked to cognitive decline, especially during aging. This new study further investigated the underlying macronutrient contributions and mechanisms that cause this.

“We found that all of the refined diets — whether they were high fat, high sugar, low fat, or low sugar, it didn’t matter — impaired memory that’s governed by the amygdala,” says co-lead author Ruth Barrientos, an investigator in the Institute of Brain, Behavior and Immunology at The Ohio State University, US.

“When we looked to see the common thread among all of those diets, the one thing that became very obvious was that they all lack fiber.”

Cognition and nutrition

For the study, published in Brain, Behavior, and Immunity, scientists fed young and aged male rats normal chow or one of five experimental diets: low-fat and low-sugar, low-fat and high-sugar, medium-fat and low-sugar, medium-fat and high-sugar, or high-fat and low-sugar.

Barrientos says a deficiency in butyrate, linked to a lack of dietary fiber, could be linked to unregulated inflammation in the brain.The researchers found that, regardless of diet type, aged rats fed a refined diet showed impaired long-term emotional memory in the amygdala compared with younger rats fed the same diet.

In the hippocampus, memory-related behavior was affected only by the high-fat and low-sugar diet.

Recent research suggests that virgin olive oil may offer protective cognitive health benefits by influencing the gut microbiome. It suggests that consuming this form of olive oil may improve cognition and diversify gut bacteria, indicating good intestinal and metabolic health.

Further research on nutrition and memory found that adding freeze-dried, red raspberry powder to a meal may help support metabolic and brain health as we age. It suggested that adding the berries regulated post-meal blood sugar spikes and boosted cognitive performance within hours. 

The no-fiber factor

When examining the rats’ guts and blood, the Ohio researchers found a significant reduction in butyrate, a key molecule produced in the gut that circulates in the blood when gut microbes break down fibers.

The scientists point to prior studies showing that butyrate has anti-inflammatory effects and can cross the blood-brain barrier. Barrientos says a deficiency in butyrate, linked to a lack of dietary fiber, could be linked to unregulated inflammation in the brain.

“What our study really brings to light is the complexity of diet and how it affects so many different things, even the brain,” says co-lead author Kedryn Baskin, assistant professor of physiology and cell biology at Ohio State. “There’s not a magic bullet, but in this case, low butyrate, as a result of a lack of fiber, is a culprit.”

Into the cellular level

The study also found that a refined diet can damage microglial mitochondria, cells with multiple functions important to memory.

These cell powerhouses influence energy production, immune responses, and neural functioning. A recent study found that the mitochondria might be a key link between psychological factors and physical health. The authors warned that defective mitochondrial function is linked to mental health issues like anxiety and post-traumatic stress disorder.

The study also found that a refined diet can damage microglial mitochondria, cells with multiple functions important to memory.The authors explain that when exposed to experimental energy demands in cell cultures, young brains’ mitochondria could adapt to changes. However, the aged brain’s cells could not adapt.

“The mitochondria are still functioning, but they’re showing depressed respiration and are functioning at a much, much lower rate in the aged compared to the young,” Baskin explains.

She further notes that although weight gain was another factor noticeable by following the refined diet, the findings “put to rest” the notion that obesity brought on by a highly processed diet is the primary driver of impaired cognition. 

“These effects on the brain after you eat something are pretty rapid. You can experience this unhealthy cognitive dysfunction well before you reach obesity.”

“Together, these findings reveal that the aged amygdala is especially sensitive to refined diet exposure and highlight microbial, metabolic, and inflammatory pathways that may underlie diet-induced cognitive decline,” asserts the study.