Research shows high-fat diets impact brain health and exacerbate cognitive decline of aging brain

Like bacteria and viruses, even unhealthy diets create systemic inflammatory responses in aging adults. Just where the inflammation takes place in the brain affects outcomes and levels of cognitive decline. Ruth M. Barrientos, PhD, associate professor in the Department of Psychiatry and Behavioral Health and Neuroscience at The Ohio State University College of Medicine, focuses research in her laboratory on determining the effect diet directly has on the brain, and specifically focuses on behavioral neuroimmunology and how vulnerabilities of the normal, aging brain can lead to lasting memory deficits. 

“Our work has shown the linkage between unhealthy diets and obesity,” Dr. Barrientos says. “But our findings dispel the idea that obesity is necessary to drive diet-related inflammation in the aging brain.”  

The study, “Obesity-Associated Memory Impairment and Neuroinflammation Precede Widespread Peripheral Perturbations in Aged Rats,” was published in the journal Immunity & Aging on BioMed Central. Barrientos and her team fed groups of young and older rats a high-fat diet (HFD) containing fast food items for two distinct time frames — three days or three months. This nutritional content aligns with the existing food environment that is driven by ultra-processed foods that create body fat even if we exercise regularly.  

“Older rats performed poorly on memory tests and exhibited signs of brain inflammation after just three days,” Dr. Barrientos says. “We showed that within three days, way before obesity sets in, there is a tremendous neuroinflammatory shift taking place.” 

How are younger animals more resilient against the negative ways in which a HFD affects their memory? Dr. Barrientos reasons it’s because they can activate compensatory anti-inflammation responses, which aged animals lack. Consumption of a HFD causes oxidative stress and inflammation and increases the activation of the transcription factor NF-κB in tissues, including adipose, liver and those in the nervous system.  

They compared the rats on the high-fat diets for three days with those who stayed on for three months and ran a test assessing two types of memory problems common in older people with dementia. Older rats displayed behaviors that indicated impairment of contextual and cued-fear memory after only three days of consuming fatty food. The behaviors persisted as they continued the HFD for three months. 

“We also observed changes in the level of cytokines, small proteins important in cell signaling, in the brains of aged rats after three days of high-fat diet, which signaled a dysregulated inflammatory response,” she says. 

To translate these findings into interventions for human patients, further studies are required to confirm and determine if humans have similar outcomes. Further studies on neuroinflammation and disrupted neuroplasticity will be integral to addressing cognitive decline and neurologic impairments.