Summary: A diet high in heavily processed foods triggered rapid neuroinflammation and memory decline in aged rats. Adding DHA, an omega-3 fatty acid, to the processed diet largely prevented those brain changes and the associated memory impairments.
Source: Ohio State
Key findings from a new animal study show that only four weeks on a highly processed food diet produced a robust inflammatory response in the brains of older rats accompanied by clear behavioral signs of memory loss.
When researchers supplemented the processed diet with the omega-3 fatty acid docosahexaenoic acid (DHA), the aged animals were largely protected from both the inflammatory changes and the memory deficits. Young adult rats did not show the same brain inflammation or cognitive problems from the processed diet during the study period.
The experimental diet was designed to mimic ready-to-eat human convenience foods that are typically refined, low in fiber and formulated for long shelf life—examples include packaged snacks, frozen entrees such as pizzas and pasta dishes, and processed deli meats containing preservatives.
Because highly processed diets are linked to obesity and type 2 diabetes in people, the authors suggest older adults may want to reduce their reliance on convenience foods and increase intake of DHA-rich options like fatty fish. The rapid onset of harm in the aging brain—visible after just four weeks in this study—highlights why attention to diet quality matters.
“Seeing these effects so quickly was concerning,” said senior author Ruth Barrientos, an investigator at The Ohio State University Institute for Behavioral Medicine Research and an associate professor of psychiatry and behavioral health. “These results indicate that a processed diet can produce abrupt memory deficits. In older adults, such rapid decline is more likely to progress to neurodegenerative conditions. Limiting processed foods and increasing omega-3 DHA in the diet may help prevent or slow that progression.”
The study appears in the journal Brain, Behavior, and Immunity.
Barrientos’ laboratory investigates how routine life events—surgery, infection or, in this case, poor diet—can trigger inflammation in the aging brain, with a particular focus on the hippocampus and amygdala. Prior work from her team showed short-term high-fat diets can impair memory and raise inflammation in older animals and that DHA concentrations are lower in aged hippocampus and amygdala.
DHA is an omega-3 polyunsaturated fatty acid commonly found in fish and seafood, where it often co-occurs with EPA (eicosapentaenoic acid). Among its roles, DHA helps modulate inflammatory responses in the brain. This study is the first to demonstrate DHA’s protective effect against neuroinflammation caused specifically by a highly processed diet in aged animals.
In the experiment, male F344 × BN rats aged 3 months (young) and 24 months (aged) were randomly assigned to one of three diets: their standard laboratory chow (32% calories from protein, 54% from wheat-based complex carbohydrates and 14% from fat); a highly processed diet (19.6% protein, 63.3% refined carbohydrates such as cornstarch, maltodextrin and sucrose, and 17.1% fat); or the same processed diet supplemented with DHA.
After 28 days, aged rats consuming the processed diet alone showed significantly increased expression of inflammatory genes in the hippocampus and amygdala. Markers elevated included IL-1β, CD11b, MHC class II, CD86, NLRP3 and complement component 3—genes linked to a strong pro-inflammatory response. These molecular changes were not present in young rats on the processed diet or in aged rats that received DHA with their processed diet.
Behavioral tests revealed corresponding cognitive impairments in the older animals on the processed diet. Aged rats quickly forgot spending time in an unfamiliar environment—a sign of impaired hippocampal-dependent contextual memory. They also failed to show anticipatory fear responses to cues predicting danger, pointing to amygdala dysfunction. Young rats did not display these impairments during the study period.
“The human amygdala contributes to memories tied to emotional events such as fear and anxiety. Dysfunction in this region can impair recognition of danger cues and lead to poor choices,” Barrientos noted.
Importantly, supplementing the processed diet with DHA prevented the rise in inflammatory gene expression and the behavioral signs of memory loss in the aged rats. The study did not determine exact DHA doses consumed because all animals had ad libitum access to food, and researchers did not measure individual intake precisely.
Both age groups gained weight on the processed diet, with aged animals gaining more than young ones. DHA supplementation did not prevent weight gain associated with the processed diet, underscoring that a supplement is not a substitute for overall dietary quality.
Barrientos emphasized this point: the findings should not be interpreted as permission to consume highly processed foods while relying on DHA supplementation. Rather, improving overall diet quality—focusing on unrefined carbohydrates, adequate fiber and nutrient-dense foods—remains the more reliable strategy to protect metabolic and brain health.
“Many products marketed as ‘low fat’ are nonetheless highly processed, low in fiber and rich in refined, low-quality carbohydrates,” she said. “Consumers should look beyond calorie and fat labels and pay attention to fiber content and the quality of carbohydrates. This study reinforces why those factors matter.”
Funding: 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 from Ohio State and Christopher Butt of Inotiv Inc., Boulder, Colorado.
About this aging and diet research news
Author: Emily Caldwell
Source: Ohio State
Contact: Emily Caldwell – Ohio State
Image: The image is in the public domain
Original Research: Closed access.
“Dietary DHA prevents cognitive impairment and inflammatory gene expression in aged male rats fed a diet enriched with refined carbohydrates” by Ruth Barrientos et al. Brain, Behavior and Immunity
Abstract
Dietary DHA prevents cognitive impairment and inflammatory gene expression in aged male rats fed a diet enriched with refined carbohydrates
Consumption of diets high in refined carbohydrates and processed ingredients—characterized by saturated fats, low fiber and long shelf life—has risen in recent decades and likely contributes to chronic disease and weight gain. Such diets have also been linked to declines in brain health and cognition across species, potentially through neuroimmune pathways. The aged brain, which already has elevated baseline inflammation, may be especially vulnerable to additional inflammatory challenges.
In this study, a processed diet enriched with refined carbohydrates consumed for 28 days impaired hippocampal- and amygdalar-dependent memory in aged (24 months) but not young (3 months) F344 × BN rats. Those memory deficits coincided with increased expression of inflammatory genes including IL-1β, CD11b, MHC class II, CD86, NLRP3, and complement component 3 in the hippocampus and amygdala. Supplementing the processed diet with the omega-3 fatty acid DHA prevented both the behavioral impairments and the inflammatory gene expression changes in aged rats, providing evidence that dietary DHA can protect the aging brain from the adverse effects of a refined-carbohydrate, processed-food diet.
The processed diet increased weight gain in both age groups, an effect amplified in aged rats. Aging was associated with alterations in hypothalamic gene expression; DHA did not prevent weight gain or alter hypothalamic gene expression in this study. Overall, the data suggest processed diets impair cognition via neuroimmune mechanisms and that DHA supplementation can ameliorate these effects in aged animals.