Many factors that contribute to cognitive decline are beyond a person’s control, such as genetics and socioeconomic factors. But ongoing research increasingly indicates that poor diet is a risk factor for memory impairment in normal aging and increases the risk of developing Alzheimer’s disease.
But when assessing how certain diets can erode brain health as we age, research on the effects of eating minimally-processed versus ultra-processed foods has been sparse. that is to say so far.
Two recent large-scale studies suggest that eating ultra-processed foods may exacerbate age-related cognitive decline and increase the risk of developing dementia. In contrast, another recent study reported that consumption of ultra-processed foods was not associated with impaired cognition in people over the age of 60.
While more research is needed, as a neuroscientist studying how diet can influence cognition later in life, I find these early studies add a new layer to consider how fundamental nutrition is to health. of the brain.
Lots of ingredients, minimal nutrition
Ultra-processed foods tend to have fewer nutrients and fiber and more sugar, fat, and salt than unprocessed or minimally processed foods. Some examples of ultra-processed foods include sodas, packaged cookies, chips, frozen dinners, flavored nuts, flavored yogurts, distilled alcoholic beverages, and fast foods. Even packaged breads, including those high in nutritious whole grains, qualify as ultra-processed in many cases due to the additives and preservatives they contain.
Another way to look at it: you probably won’t find the ingredients that make up most of these foods in your kitchen.
But don’t confuse ultra-processed foods with processed foods, which retain most of their natural characteristics despite having undergone some form of processing – such as canned vegetables, dried pasta, or frozen fruit.
Analyze research
In a December 2022 study, researchers compared the rate of cognitive decline over about eight years between groups of people who ate different amounts of ultra-processed foods.
At the start of the study, more than 10,000 participants living in Brazil reported their eating habits over the previous 12 months. Then, over the next few years, the researchers assessed participants’ cognitive performance with standard tests of memory and executive function.
Those who ate a diet containing more ultra-processed foods at the start of the study showed slightly greater cognitive decline than those who ate little or no ultra-processed food. This was a relatively modest difference in the rate of cognitive decline between the experimental groups. It is not yet clear whether the small difference in cognitive decline associated with higher consumption of ultra-processed foods will have a significant effect at an individual person level.
The second study, with around 72,000 participants in the UK, measured the association between consumption of ultra-processed foods and dementia. For the group eating the highest amounts of ultra-processed foods, about 1 in 120 people were diagnosed with dementia over a 10-year period. For the group that ate little to no ultra-processed foods, that number was 1 in 170.
Research examining the relationship between health and ultra-processed foods uses the NOVA classification, which is a categorization system based on the type and extent of industrial food processing. Some nutritionists have criticized the NOVA classification for not having clear definitions of food processing, which could lead to misclassification. They also argue that the potential health risks of eating ultra-processed foods could be explained by low fiber and nutrient levels and high levels of fat, sugar and salt in the diet rather only by the amount of transformation.
Many ultra-processed foods are high in additives, preservatives, or colorings, while exhibiting other characteristics of an unhealthy diet, such as low in fiber and nutrients. Thus, it is unclear whether eating foods that have undergone more processing has an additional negative impact on health beyond a low-quality diet.
For example, you might eat a burger and fries from a fast-food chain, which are high in fat, sugar, and salt, and are ultra-processed. You could prepare this same meal at home, which could also be high in fat, sugar and salt, but not ultra-processed. Further research is needed to determine if one is worse than the other.
Brain-healthy diets
Even when the processes that lead to dementia do not occur, the aging brain undergoes biochemical and structural changes that are associated with worsening cognition.
But for adults over 55, eating a healthier diet could increase the likelihood of maintaining better brain function. In particular, the Mediterranean diet and the ketogenic diet are associated with better cognition in old age.
The Mediterranean diet emphasizes eating plant-based foods and healthy fats, such as olive oil, seeds, and nuts. The ketogenic diet is high in fat and low in carbs, with the main source of fiber being vegetables. Both diets minimize or eliminate sugar intake.
Our research and the work of others shows that both diets can reverse some of these changes and improve cognitive function, possibly by reducing harmful inflammation.
Although inflammation is a normal immune response to injury or infection, chronic inflammation can be detrimental to the brain. Studies have shown that excess sugar and fat can contribute to chronic inflammation, and ultra-processed foods can also exacerbate harmful inflammation.
Another way diet and ultra-processed foods can influence brain health is through the gut-brain axis, which is the communication that occurs between the brain and the gut microbiome, or community of microorganisms. that live in the digestive tract.
Not only does the gut microbiota aid in digestion, but it also influences the immune system, while producing hormones and neurotransmitters essential for brain function.
Studies have shown that ketogenic and Mediterranean diets alter the composition of microorganisms in the gut in a way that benefits the person. Consumption of ultra-processed foods is also associated with alterations in the type and abundance of gut microorganisms that have more harmful effects.
The uncertainties
Unraveling the specific effects of individual foods on the human body is difficult, in part because maintaining tight control over people’s diets is problematic when studying them over long periods of time. Additionally, randomized controlled trials, the most reliable type of study to establish causation, are expensive to conduct.
So far, most nutritional studies, including these two, have only shown correlations between eating ultra-processed foods and health. But they cannot rule out other lifestyle factors such as exercise, education, socioeconomic status, social connections, stress, and many other variables that may influence cognitive function. .
This is where laboratory studies using animals are incredibly useful. Rats show cognitive decline in old age that parallels humans. It is easy to monitor the diets and activity levels of rodents in a laboratory. And the rats go from middle age to old age in a few months, which shortens the study time.
Laboratory animal studies will help determine if ultra-processed foods play a key role in the development of cognitive impairment and dementia in humans. As the world’s population ages and the number of older adults with dementia increases, this knowledge cannot come soon enough.