Highly Processed, Carbohydrate-Rich Foods Curb Cognition in the Aging Brain — and the Omega-3 Fat DHA May Help

What do chips, soda, and hot dogs have in common? While you probably know that these foods are processed and can contribute to poor health outcomes and weight gain, it’s lesser-known that they can affect cognition. Often referred to as the standard American or Western diet, these foods are packaged and preserved for long shelf lives, including potato chips and other snacks, frozen entrees like pizza or nuggets, and deli meats — and new research shows how these not-so-healthy foods can actually eat away at our brains.   

In a first-of-its-kind study, researchers out of Ohio State University looked at how consuming a diet full of processed foods and refined carbohydrates for just four weeks impacted brain health, behavior, and inflammatory activity in aged rats. Published in the journal Brain, Behavior, and Immunity, Butler and colleagues find that not only does this unhealthy diet drastically and rapidly impair cognition and increase inflammation, but also that there is a simple way to fix it — a compound called DHA (docosahexaenoic acid). Levels of DHA, a member of the healthy fat family known as omega-3s, tend to decrease in the aging brain; this research shows that supplementing with DHA ameliorates almost all of the negative health outcomes induced by a highly processed and unhealthy diet.

The Brain-Building Benefits of DHA 

Found primarily in the diet from fatty fish like salmon and sardines, DHA is well-known for its ability to promote healthier inflammatory responses in the body — and the brain is no exception. DHA helps facilitate the signaling and growth of the brain cells that transmit information (neurons), supports memory and learning, and plays a crucial role in composing strong cell barriers called membranes. 

Supplemental DHA has been previously utilized to correct or aid certain brain disorders or symptoms. However, whether this omega-3 fat also protects against diet-induced insults to cognition is unknown — until now, with this recent research by Butler and colleagues.

The Ohio-based research team split young (about 20 in human years) and aged (approximately 70 in human years) male rats into three groups: one eating a standard diet, one eating a highly-processed diet filled with refined carbohydrates that mimicked the standard American diet, and one eating the unhealthy diet plus supplemental DHA. 

After four weeks on these diets, Butler and colleagues tested the rats on tasks involving two brain regions, the hippocampus and the amygdala. While the hippocampus is the region highly involved with learning and memory, the amygdala is vital for processing emotions and regulating behavior. As senior study author Ruth Barrientos, an investigator in The Ohio State University Institute for Behavioral Medicine Research, states, "The amygdala in humans has been implicated in memories associated with emotional — fear- and anxiety-producing — events. If this region of the brain is dysfunctional, cues that predict danger may be missed and could lead to bad decisions.”

Processed Foods Curb Cognition and Increase Inflammation

The research team found that aged rats on the processed foods diet (PD) exhibited significant deficits in tests for behavior-related memory. Compared to the younger rats, the older animals forgot that they had already spent time in a new space just a few days prior (a measure of contextual memory and hippocampal function) and did not show fear-related behavior to a danger cue, indicating declining amygdala function. 

These negative impacts on cognition were seen quite rapidly, after just four weeks of eating unhealthfully. As Dr. Barrientos states, "The fact we're seeing these effects so quickly is a little bit alarming.”

However, they then found that supplemental DHA effectively prevented all of the memory- and behavior-related deficits. These results exemplify that a highly-processed diet impairs cognition and memory, especially in the hippocampus and amygdala — and that supplemental DHA may act as a promising therapeutic compound for supporting brain function and behavior with age. 

Next, Butler and colleagues looked at how the PD or DHA altered inflammatory activity. Eating the processed diet increased several markers of inflammation in the hippocampus and amygdala, including the proinflammatory cytokine compounds interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α); supplementing with DHA brought their levels back down. 

Lastly, the research team assessed weight changes in the rats, unsurprisingly finding that eating the processed foods diet significantly contributed to weight gain — but only in the older rats. In contrast to other studies which have found DHA to prevent diet-induced weight gain, the DHA-supplemented rats in this study did not see the same benefit. 

Maintaining Memory, One Bite of Salmon at a Time

This study demonstrates that just four weeks on a highly processed and refined carbohydrate-rich diet can cause detrimental changes to brain health, cognition, inflammation, and behavior. The good news? Supplementing with the omega-3 fat DHA may be sufficient to reverse these markers.

As Barrientos concludes, "These findings indicate that consumption of a processed diet can produce significant and abrupt memory deficits — and in the aging population, rapid memory decline has a greater likelihood of progressing into [poor cognitive function]. By being aware of this, maybe we can limit processed foods in our diets and increase consumption of foods that are rich in the omega-3 fatty acid DHA to either prevent or slow that progression." Notably, the amount of DHA consumed by the aged rats would translate to approximately 500 mg per day in a 130-pound human — an amount easily achieved by eating about two ounces of salmon. In this case, it appears that a tiny serving of fatty fish per day may indeed help keep the neurologist away. 

References: 

Butler MJ, Deems NP, Muscat S, Butt CM, Belury MA, Barrientos RM. Dietary DHA prevents cognitive impairment and inflammatory gene expression in aged male rats fed a diet enriched with refined carbohydrates. Brain Behav Immun. 2021;98:198-209. doi:10.1016/j.bbi.2021.08.214