Nutrition-related dementia research has generated a flood of promising data in recent years. Studies tend to focus on diet quality, based on the amount of certain nutrients or ingredients (e.g., omega-3 fatty acids, antioxidants, etc.) or on dietary patterns (e.g., the Mediterranean or MIND diets, which recommend high fruit and vegetable consumption, whole grains, etc.) and have already identified their potential beneficial effects on brain health. Recently, many people’s diets have changed, and researchers are beginning to focus on another component of the diet: ultra-processed foods, also known as fast foods, and the associated risk to neuronal health.
Fast food and ultra-processed food – what is it?
This is not just about the quick burger from various gastro chains, but rather a large part of the food in our supermarkets. This includes all foods that are available on the shelves as finished or packaged products. This includes ready-made pasta or rice dishes, canned goods, soft drinks, salty pastries and sweets, packaged baked goods, ready-made spreads, ready-made sauces such as ketchup and mayonnaise, or cereals and breakfast cereals. Consumption of highly processed foods has increased massively in recent years. They literally attract consumers because they are uncomplicated, quick to prepare, cost-effective and taste delicious.
How can the level of processing of food be classified for scientific studies?
The classification of foods from “unprocessed” to “highly processed” and the scientific validity of this classification has indeed proven to be a major challenge. One possible concept that serves as the basis for many scientific studies today is the so-called NOVA classification, which divides foods and beverages into four groups according to the level of processing :
Group 1: Unprocessed and minimally processed foods:
Pure, unprocessed to minimally processed foods: e.g., fresh fruits and vegetables, meat, fish, including in minced, dried, frozen form.
Group 2: Processed culinary ingredients:
Foods derived from Group 1 (or nature), i.e., substances, used for cooking and seasoning Group 1 and not intended for direct consumption: e.g. vegetable oils (pressed from olives, nuts, seeds) etc., butter (from milk), sugar (from sugar beets) or even salt
Group 3: Processed foods:
Prepared (including preserved) foods from groups 1 and 2: e.g., canned fruits and vegetables, cheese, salted roasted nuts, unpackaged bread, freshly cooked meals
Group 4: Ultra-processed foods:
Ultra-processed foods that are manufactured exclusively on an industrial scale, usually through a series of industrial processes: e.g., all ready-to-eat and packaged baked goods, instant noodles, hot dogs, sausages, mayonnaises, sauces, snack foods such as chips, potato chips, and crackers, candy, ice cream, breakfast cereals, and sodas.
For the last group, it is characteristic that the foods have an extremely high fat and/or sugar content, with additional sugar usually being added in the form of syrups containing fructose. The valuable food ingredients, on the other hand, such as protein, fiber, micronutrients and the protective phytochemicals, have been removed from these foods to a high degree in the course of processing. In addition, these foods usually contain higher amounts of toxic contaminants such as mineral oils from the mechanical processing, softeners from the packaging, acrylamide due to the strong heating. In addition, not least for the optimal condition of the end product, such as appearance, consistency, taste, etc., there are often a large number of food additives.
How does a diet of highly processed foods affect brain health?
A recent epidemiological study examined the effect of replacing highly processed foods in the diet with unprocessed or minimally processed foods on cognitive performance .
The study involved 72,083 adults, all aged 55 years or older, who did not have dementia at baseline. Each study participant completed dietary questionnaires through Oxford WebQ, a validated web-based dietary program. This can capture information on a variety of foods and beverages that participants consumed in the previous 24 hours. Study authors defined highly processed foods based on the previously described NOVA classification, which categorizes foods and beverages into four groups based on the degree of processing.
The result was that a diet containing 10 % highly processed foods (foods in group 4 according to the NOVA classification) increased the risk of dementia overall by 25 % and the risk of vascular (cardiovascular related) dementia by 28 %. Although not significant, a 14 % increase in Alzheimer’s risk was also observed.
The reverse case was also tested: When the highly processed foods from group 4 were substituted with unprocessed or minimally processed foods from group 1, the risk of dementia and vascular dementia (but not Alzheimer’s disease) was actually reduced. A dose-response relationship was evident, as the risk reduction increased proportionally with the percentage of substitution: thus, the risk of dementia was 10 % lower with a 5 % substitution, 19 % lower with a 10 % substitution, and as much as 34 % lower with a 20 % substitution.
The findings of this group of researchers were also confirmed by other studies that looked at the effects of highly processed foods on cognition:
- A Brazilian team presented a study at the Alzheimer’s Association International Conference that involved 8,160 people who did not have dementia and were about 51 years old on average over a nine-year period. Consumption of the highly processed foods was recorded by questionnaires. It was found that the group that consumed the largest amount of highly processed foods (more than 20 % of daily caloric intake) showed a significantly higher decline in memory performance as well as executive functions than those who consumed a smaller amount of these foods .
- In a recent study from Australia with 3,632 healthy participants aged at least 60 years , which also investigated the relationship between the consumption of highly processed foods and their effect on cognitive performance, a significant effect was detected. This was reflected in poorer performance on the so-called Animal Fluency Test – a special cognition test for older adults that assesses language and executive functions.
- In an Israeli study  , 568 diabetes type 2 patients who were 65 years and older but did not have dementia were examined. Here, different food groups were also recorded in terms of their effect on cognitive performance. The result of this research project was that a higher consumption of highly processed sausages, industrially produced bread and highly processed oils was highly significantly associated with a faster decline in executive functions and global cognition. This is not surprising, since dementia is a complex disease with numerous risk factors in the metabolic processes: in fact, we have already reported in detail on the links between the sugar metabolism disorder diabetes mellitus and Alzheimer’s disease in particular.
These studies, like all epidemiological studies, represent a step toward understanding the mechanistic links between diet and dementia. They can also be seen as more pieces in a larger puzzle: for example, the cited studies add to the large body of evidence on the adverse health effects associated with the consumption of highly processed foods, including cardiovascular disease, diabetes, overweight, obesity, cancer, and all-cause mortality. One review publication reported 37 such studies, in each of which there was at least one statistically significant association between the consumption of highly processed foods and an adverse health outcome, whereas no beneficial effects were reported in any study . Thus, one can imagine what the increasing consumption of these foods would mean for overall health and the health care system.
However, this implies conversely that a shift to lower consumption of ultra-processed foods (group 4) and higher consumption of unprocessed to low-processed foods (groups 1-3) may help prevent dementia and many other chronic diseases. Given that many people’s lifelong eating habits begin in childhood, early changes in diet would be particularly effective in dementia and disease prevention, especially because there is still no effective drug treatment for dementia.
In the face of this overwhelming burden of evidence, physicians should advise their patients to eat fresh foods and cook at home rather than buy convenience foods and snacks. Further, this substantial and ever-growing body of evidence on how bad highly processed foods are for health would be an argument for making the “health value” of foods dependent on the degree of processing and making this transparent to consumers through appropriate labeling. This should also be considered without fail in the development of future dietary recommendations and guidelines, to prevent the potential cost burden on our health care system in good time.
Conclusion – what these study results may mean for your brain health:
Recent observational studies have shown that people who eat a diet with a defined proportion of ultra-processed foods suffer cognition impairment and therefore have a significantly higher risk of developing dementia. Accordingly, the scope of influence on the development of dementia by the way one eats is enormous. What sounds like a disadvantage at first glance is a particular advantage. This is because it is not genes or age that primarily determine whether we develop dementia, but our own dietary behavior, which we can actively influence ourselves. The study results prove that even changes in small areas – the replacement of a few foods – have significant effects on brain health. It doesn’t mean an absolute renunciation and massive restrictions of previous habits, but it does mean a reduction and a conscious decision against certain products and for our own health.
So, start today: Replace your bag of chips with an apple every day, and cook for yourself rather than buying ready-made meals. Your brain health will thank you for this!
- ↑ Monteiro CA, Cannon G, Levy RB, et al (2019) Ultra-processed foods: what they are and how to identify them. Public Health Nutrition: 22(5), 936–941 doi:10.1017/S1368980018003762
- ↑ Li H, Yang H, Zhang Y, et al. Association of ultraprocessed food consumption with risk of dementia: A prospective cohort (2022) Neurology September 06; 99 (10) DOI: https://doi.org/10.1212/WNL.0000000000200871
- ↑ Goncalves N, Ferreira NV, Khandpur N, et al. (2022) Consumption of ultra-processed foods and cognitive decline in the ELSA-Brazil study: A prospective study. AAIC Abstract 63301 https://alz.confex.com/alz/2022/meetingapp.cgi/Paper/63301.
- ↑ Cardoso BR, Machado P, Steele EM (2022) Association between ultra-processed food consumption and cognitive performance in US older adults: a cross-sectional analysis of the NHANES 2011-2014. Eur J Nutr Jul 1. In Print doi: 10.1007/s00394-022-02911-1.
- a id=”cite_note-5″ href=”#cite_backlink-5″>↑ Weinstein G, Vered S, Ivancovsky-Wajcman D, Springer RR, et al. (2021) Consumption of ultra-processed food and cognitive decline among older adults with type-2 diabetes. J Gerontol A Biol Sci Med Sci, Mar 19, doi: 10.1093/gerona/glac070.
- ↑ Leonie Elizabeth, Machado P, Zinöcker M, Baker P, Lawrence M (2020) Ultra-Processed Foods and Health Outcomes: A Narrative Review. Nutrients 12, 1955; doi:10.3390/nu12071955