Could eating a lot of ultraprocessed food affect how your brain ages? A growing body of research suggests there could be a connection, but scientists aren't yet able to say that these foods directly cause cognitive decline or dementia.
A new review published in the Annual Review of Nutrition brings together what researchers know so far about ultraprocessed foods and brain health as people age. The overall picture raises questions worth investigating, but it also reveals how much remains uncertain. Most of the evidence comes from studies that can identify links between diet and health but can't prove that one causes the other.
Ultraprocessed foods make up a large part of the modern food supply, but the category itself is broad. It can include everything from sweetened drinks and packaged snacks to breads, cereals and other foods people regularly buy at the grocery store. That variety is important because foods within the category aren't necessarily nutritionally alike.
“A lot of people inside and outside of science are worried about the effects that food processing and artificial food additives might have on health, but it is hard to know what reported health effects are real and which ones are not,” lead author Owen Carmichael of LSU’s Pennington Biomedical Research Center said in a news release.
The review found relatively little research looking specifically at ultraprocessed food consumption and changes in thinking and memory over time.
One study followed more than 10,000 adults in Brazil for a median of eight years. People who got more than 19.9% of their daily calories from ultraprocessed foods experienced faster decline in some areas of thinking, but only among those who didn't closely follow a MIND-style diet, an eating pattern centered on foods associated with brain health.
Another study followed 568 older adults with type 2 diabetes for an average of 5.3 years. Higher consumption of certain types of ultraprocessed foods was associated with faster cognitive decline, but total ultraprocessed food consumption was not.
That distinction matters. If some types of ultraprocessed foods are associated with poorer outcomes while others aren't, simply counting everything in the category together may miss important differences.
Other large studies have linked greater ultraprocessed food consumption with a higher risk of dementia, including Alzheimer's disease and vascular dementia. Researchers have also found associations between some dietary patterns and differences in brain structure. The results, however, haven't been completely consistent.
And none of those associations proves that ultraprocessed foods caused the changes.
People who eat more ultraprocessed foods may differ from people who eat less of them in many ways that could also affect brain health. Their overall diets may be different, for example, making it difficult to separate the possible effects of processing from the effects of the foods and nutrients people are consuming.
Researchers are exploring several possible explanations for the associations they have observed, including differences in nutrition, metabolic health and ingredients used in some ultraprocessed foods. But those ideas are still being investigated. Scientists don't yet have a single explanation showing why greater ultraprocessed food consumption might be connected with brain aging.
Getting a definitive answer will also take time. Cognitive decline and dementia can develop over many years, making it difficult to conduct the kinds of long-term controlled studies that could provide stronger evidence of cause and effect.
For now, the research points to a possible connection rather than a settled conclusion. Higher ultraprocessed food consumption has been associated with poorer brain health in several studies, but that doesn't mean eating a particular packaged food causes cognitive decline. It also doesn't show that eliminating ultraprocessed foods would prevent dementia.
The bigger question now is whether the associations researchers are seeing are driven by processing itself, particular foods or ingredients, the overall quality of people's diets or some combination of those factors. Answering that could ultimately be more useful than treating every ultraprocessed food as if it affects the brain in the same way.
The review was facilitated by professional interest groups within the Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment. Carmichael chairs one of those groups and reported a consulting agreement with Clario Inc. Two other authors reported roles with Alzheimer's Association groups, including one who also serves on the board of Dementia Alliance International.