Complex carbohydrates take longer to digest and have many nutritional benefits that help regulate blood sugar levels.
By contrast, refined carbohydrates take less time to digest, have fewer nutritional benefits, and can increase blood sugar levels and increase the risk of health conditions such as type 2 diabetes and heart disease.
Previous research has shown that aged, but not young, rats eating a short-term high fat diet had impaired memory and increased levels of inflammation in various parts of the brain. The researchers found, however, that a dietary intervention can reduce this.
Scientists do not know whether DHA protects against carbohydrate-related effects on cognition and neuroinflammation.
Recently, researchers from Ohio State University (OSU) and Inotiv Inc. conducted a study to understand the mechanisms behind the neurologic effects of processed diets and whether omega-3 supplementation could improve these effects.
They found that processed food diets impaired memory function among aged, but not young, rats and that this occurred alongside increased signs of inflammation. Omega-3 supplementation, however, improved these effects.
When asked whether these results were surprising, Dr. Ruth Barrientos, Ph.D., lead author of this research and associate professor at OSU, told Medical News Today:
“Yes, many studies, including our own, have focused on high fat and high sugar diets being detrimental to memory function, but few have examined the short-term effects of a highly processed diet. Given that many processed diets are low in fat, we had our doubts that we’d see any significant results. Not only did we observe very significant memory impairments, [but] we also saw significant weight gain with this diet.”
MNT also spoke with Dr. Andile Khathi, academic leader of Human Body and Function at the University of KwaZulu-Natal in South Africa, who was not involved in the present study. He said,
“I think we’ve known for a while that prolonged consumption of highly processed foods can be detrimental to the body, but this study shows just how bad this can be for the brains of [older adults].”
“Other studies have shown how beneficial omega-3 can be, but this study has gone a step further to show how its consumption can be good for mental health,” he added.
The research appears in the journal Brain, Behavior, and Immunity.
The researchers obtained 3- and 24-month old rats for the research. As female rats were not available in the older age category at the time of the study, the researchers exclusively used male rats.
At the beginning of the research, the younger rats weighed around 300 grams (g) on average, whereas the older rats weighed around 550 g.
The rats were housed two to a cage and randomly assigned to continue eating either a regular diet including 54% complex carbohydrates, a processed food diet including 63.3% refined carbohydrates, or a processed food diet and DHA supplements for 28 days.
After this period, the scientists placed the rats separately in a conditioning chamber, where the rats heard a tone for 15 seconds and then received a 2-second footshock. Four days later, the scientists reintroduced the rats to the cage and the sound to assess their fear response.
While there were no differences in freezing behavior between the different groups of rats during the conditioning phase, the researchers observed that older rats exclusively fed a processed diet froze significantly less in both fear experiments than older animals on other diet plans.
The researchers also found that both groups of rats that ate a processed food diet experienced weight gain similar to that of the rats on the alternative diet. Moreover, older animals were more affected than younger ones.
After these experiments, the researchers isolated different areas of the rats’ brains to analyze their RNA.
These analyses revealed that the rats that ate a processed food diet alone had significantly higher inflammatory gene expression than those that consumed the alternative diet, or a processed food diet with DHA supplementation.
The authors found, however, that DHA supplementation did not impact all genes that the study investigated.
According to the researchers, this means that DHA supplements do not necessarily offset the negative effects of highly refined foods and that people should focus on overall diet improvement by increasing complex carbohydrate and fiber intake.
“Processed and refined foods are unfamiliar to our gut microbiome, which has evolved over thousands of years, so these foods can provoke an inflammatory immune response, almost as if the processed food was a pathogen,” Dr. Barrientos explained.
“This peripheral immune response can easily trigger inflammation in the brain, and due to some brain immune cells in the aging brain being sensitized, this neuroinflammation can become exaggerated. Exaggerated neuroinflammation in turn is known to impair various memory-forming and maintenance mechanisms,” she added.
“The omega-3 fatty acid DHA and its metabolites are known to resolve inflammation, and we believe that explains the protective effects.”
– Dr. Ruth Barrientos
“Many studies have shown how the chronic consumption of refined carbohydrates and saturated fats can lead to various metabolic aberrations underpinned by inflammation,” Dr. Khathi explained. “The hippocampus, which is responsible for memory, is quite sensitive to metabolic changes, especially in [older adults].”
“This could explain why the consumption of these highly processed foods has such negative effects on memory. The consumption of unsaturated/polyunsaturated fats has been found to be good for various parts of the body, so it stands to reason that it could be good for the protection of brain structures such as the hippocampus,” he added.
The researchers conclude that a processed food diet with refined carbohydrates impairs cognitive function, increases neuroinflammatory gene expression, and increases weight gain in aged rats. They also found that DHA supplementation can reduce this effect.
One limitation of the study is that the researchers do not know exactly how much food each rat ate, as the rats were housed two to a cage.
“While intriguing, this research needs to be replicated in humans to determine if the same effect is seen,” Dr. Claire Sexton, D.Phil., director of Scientific Programs and Outreach at the Alzheimer’s Association, who was not involved in the study, told MNT. She continued,
“To date, there isn’t a single food, ingredient, or supplement that — through rigorous scientific research — has been shown to prevent, treat, or cure Alzheimer’s or other dementia in humans.”
Dr. Sara Imarisio, head of research at Alzheimer’s Research UK, who was not involved in the study, also spoke with MNT. She said, “What is not clear from the study is whether DHA could have similar effects in people or whether it acts against biological mechanisms that cause dementia.”
“A small number of studies have specifically linked omega-3 to better heart health and circulation, but research has so far not conclusively shown that taking omega-3 can reduce memory and thinking problems.”
Dr. Imarisio continued, “This early stage study can’t tell us whether DHA may have an impact on diseases like Alzheimer’s, and further work is needed to explore any possible link.”
In future studies, the researchers aim to examine and define the effects of processed food diets on the gut and to include female rats in their research.