Four weeks on a diet with highly processed food led to a strong inflammatory reaction in the brain of aging rats, which was accompanied by behavioral signs of memory loss, a new study has found.
Researchers also found that supplementing the processed diet with the omega-3 fatty acid DHA prevented memory problems and reduced the inflammatory effects almost exclusively in older rats.
Neuroinflammation and cognitive problems were not detected in young adult rats eating the processed diet.
The study diet mimicked ready-to-eat human foods that are often packaged in long shelf life, such as potato chips and other snacks, frozen entrees like pasta dishes and pizzas, and delicacies that contain preservatives.
Highly processed diets are also linked to obesity and type 2 diabetes, suggesting that older consumers may want to drop down convenience foods and add foods rich in DHA, such as salmon, to their diet, researchers say – especially considering harm to the older brain in this study was evident in just four weeks.
“The fact that we are seeing these effects so quickly is a little alarming,” said senior study author Ruth Barrientos, an investigator at Ohio State University Institute for Behavioral Medicine Research and associate professor of psychiatry and behavioral health.
These findings suggest that consuming a processed diet can produce significant and sudden memory deficits – and in the aging population, rapid memory loss is more likely to develop into neurodegenerative diseases such as Alzheimer’s disease. By being aware of this, we may be able to limit processed foods in our diet and increase the consumption of foods rich in omega-3 fatty acid DHA, to either prevent or slow that development. ”
The research is published in the journal Brain, Behavior, and Immunity.
Barrientos’ laboratory is investigating how everyday events – such as surgery, an infection or in this case an unhealthy diet – can trigger inflammation in the aging brain with a specific focus on the hippocampal and amygdala regions. This work builds on her previous research suggesting that a short-term, fatty diet may lead to memory loss and encephalitis in older animals, and that DHA levels are lower in the hippocampus and amygdala in the older rat brain.
DHA, or docosahexaenoic acid, is an omega-3 fatty acid present along with eicosapentaenoic acid (EPA) in fish and other shellfish. Among DHA’s many functions in the brain is a role in averting an inflammatory reaction – this is the first study of its ability to work against encephalitis caused by a processed diet.
The research team randomly assigned 3-month-old and 24-month-old male rats to their normal chow (32% calories from protein, 54% from wheat-based complex carbohydrates and 14% from fat), a highly processed diet (19.6% of calories from protein, 63 , 3% from refined carbohydrates – corn starch, maltodextrin and sucrose – and 17.1% from fat) or the same processed diet supplemented with DHA.
Activation of genes associated with a strong proinflammatory protein and other inflammatory markers was significantly elevated in the hippocampus and amygdala in the older rats that ate the processed diet alone compared to young rats on any diet and older rats that ate DHA-supplemented processed foods.
The older rats on the processed diet also showed signs of memory loss in behavioral experiments that were not evident in the young rats. They forgot to have spent time in an unknown space within a few days, a sign of contextual memory problems in the hippocampus, and did not show anticipatory fear behavior to a danger signal, suggesting that there were abnormalities in the amygdala.
“Amygdala in humans has been implicated in memories associated with emotional-fear- and anxiety-producing events. If this region of the brain is dysfunctional, traces that predict danger may be missed and could lead to poor decisions, ”Barrientos said.
The results also showed that DHA supplementation of processed foods ingested by the older rats effectively prevented the elevated inflammatory response in the brain as well as behavioral signs of memory loss.
Researchers do not know the exact dosage of DHA – or the exact calories and nutrients – taken by the animals, all of which had unlimited access to food. Both age groups received significant weight on the processed diet, with old animals receiving significantly more than the young animals. DHA supplements had no preventative effect on weight gain associated with eating heavily processed foods.
It was a key finding: Barrientos warned against interpreting the results as a permit for consumers to enjoy processed foods as long as they take a DHA supplement. A better bid to prevent more negative effects of highly refined foods would be to focus on the overall dietary improvement, she said.
“These are the kinds of diets that are advertised as being low in fat, but they are highly processed. They have no fiber and have refined carbohydrates, which are also called low-quality carbohydrates, ”she said. “People who are used to looking at nutritional information need to pay attention to the fiber and quality of carbohydrates. This study really shows that these things are important. ”
This research was supported by the National Institute on Aging, the National Institute of Dental and Craniofacial Research and the Ohio Agricultural Research and Development Center. Co-authors include Michael Butler, Nicholas Deems, Stephanie Muscat and Martha Belury of Ohio State and Christopher Butt of Inotiv Inc. in Boulder, Colorado.