Four weeks on a diet of ‘highly processed food’ resulted in a ‘strong inflammatory response’ in the brains of aging rats and was accompanied by behavioural signs of memory loss, researchers from Ohio State University have found. Neuroinflammation and cognitive problems were not detected in young adult rats that ate the processed diet.
The study diet was designed to mimic ready-to-eat human foods such as potato chips and other snacks, frozen ready meals like pasta and pizza dishes, and deli meats that are high in preservatives. The study authors noted that this latest research adds to a growing body of evidence pointing to the negative health consequences of ultra-processed foods, which have also been associated with obesity and type 2 diabetes.
However, they also found that supplementing a processed diet with omega-3 fatty acid DHA prevented memory problems and reduced the inflammatory effects almost entirely in older rats.
DHA, or docosahexaenoic acid, is an omega-3 fatty acid that is present along with eicosapentaenoic acid (EPA) in fish and other seafood. Among DHA’s multiple functions in the brain is a role in fending off an inflammatory response. This is the first study of its ability to act against brain inflammation brought on by a processed diet.
The study authors suggested older consumers might want to ‘scale back on convenience foods and add foods rich in DHA’ such as salmon and oily fish to their diets. This is especially the case considering the harm to the aged brain in this study was evident in only four weeks, they added.
“The fact we’re seeing these effects so quickly is a little bit alarming,” said senior study author Ruth Barrientos, an investigator in The Ohio State University Institute for Behavioural Medicine Research and associate professor of psychiatry and behavioural health.
Barrientos’ lab studies how everyday life events – such as surgery, an infection or, in this case, an unhealthy diet – might trigger inflammation in the aging brain, with a specific focus on the hippocampus and amygdala regions. This work builds on her previous research suggesting a short-term, high-fat diet can lead to memory loss and brain inflammation in older animals, and that DHA levels are lower in the hippocampus and amygdala of the aged rat brain.
“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 neurodegenerative diseases such as Alzheimer’s disease. 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.”
Effect of processed diet worsens with age
The research was carried out on 3-month-old and 24-month-old rats, who were randomly assigned their ‘normal diet’ consisting of 32% calories from protein, 54% from wheat-based complex carbs and 14% from fat; a ‘highly processed’ diet of 196.% calories from protein, 63.3% from refined carbs and 17.1% from fat; and a processed diet supplemented with DHA.
Activation of genes linked to a pro-inflammatory protein and other markers of inflammation were ‘significantly elevated’ in the hippocampus and amygdala of the older rats that ate the processed diet alone compared to young rats on any diet and older rats on a diet supplemented with DHA.
“The older rats on the processed diet also showed signs of memory loss in behavioural experiments that weren’t evident in the young rats. They forgot having spent time in an unfamiliar space within a few days, a sign of problems with contextual memory in the hippocampus, and did not display anticipatory fear behaviour to a danger cue, which suggested there were abnormalities in the amygdala.”
Barrientos said if the same responses are triggered in humans, the consequences for individuals who eat highly processed diets could be significant. “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,” she explained.
The results also showed that DHA supplementation of the processed-food diets consumed by the older rats effectively prevented the elevated inflammatory response in the brain as well as behavioural signs of memory loss.
All age group’s gained a ‘significant’ amount of weight on the diet of processed food, with old animals gaining a substantial amount more than the young animals. And DHA supplementation did not impact the level of weight gain.
Barrientos said this is an important takeaway – cautioning that DHA supplementation isn’t effectively a blank cheque to eat highly processed food. A better approach to prevent multiple negative effects of highly refined foods would be focusing on overall diet improvement, she said.
“These are the types of diets that are advertised as being low in fat, but they’re highly processed. They have no fibre and have refined carbohydrates that are also known as low-quality carbohydrates,” she said. “Folks who are used to looking at nutritional information need to pay attention to the fibre and quality of carbohydrates. This study really shows those things are important.”
This research was published in journal Brain Behavior and Immunity and supported by the National Institute on Aging, the National Institute of Dental and Craniofacial Research, and the Ohio Agricultural Research and Development Center.
Brain Behavior and Immunity
Dietary DHA prevents cognitive impairment and inflammatory gene expression in aged male rats fed a diet enriched with refined carbohydrates