A new review suggests that ultraprocessed foods may be linked to issues such as depression, dementia risk, and brain shrinkage, although it does not establish direct causation. These foods, including sodas, packaged snacks, and frozen meals, account for more than half of the daily caloric intake for many Americans. Prior studies have already associated ultraprocessed foods with various heart and metabolic issues, and this review raises additional concerns for cognitive health in older adults.
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Owen Carmichael, a dementia researcher at LSU’s Pennington Biomedical Research Center, led the review along with 26 co-authors from various countries. The analysis did not involve new experiments but instead synthesized existing studies, brain scans, and animal research to assess the current understanding and identify knowledge gaps. Carmichael stated, "The bottom line is that some of the data is concerning, but there are still many unanswered questions about how these relationships work and what they mean for long-term cognitive health."
Defining ultraprocessed foods is challenging since nearly all packaged foods are processed to some extent. Typically, ultraprocessed foods are made from refined ingredients and often contain added sugars, fats, salts, and various additives, while losing much of their natural nutrients. Brazil's Nova system is frequently used to categorize food processing levels, although critics argue that it lacks precision, complicating comparative studies.
Consumption levels of ultraprocessed foods vary by country, making up around 42% of daily calories in Australia and 21.5% in Brazil, while in the United States, the figure is approximately 55% to 58%. Current human studies have established associations rather than proof of direct links to mental health outcomes. For instance, a study in Brazil tracking 10,775 adults over eight years found decreased cognitive function associated with high consumption of ultraprocessed foods, particularly among those not adhering to the MIND diet, which emphasizes plant-based foods.
In another study involving older adults in Israel with type 2 diabetes, a link was found between certain ultraprocessed products and accelerated cognitive decline. The UK Biobank revealed that each additional 25 grams of processed meat increased dementia risk by 44% to 52%, with a separate analysis suggesting that replacing 10% of ultraprocessed calories with unprocessed food could reduce dementia risk by 19%. However, caution is urged, as these studies do not fully differentiate between food intake and other health factors.
Brain imaging studies present mixed results. Some have found associations between sugary drinks and reduced brain volume or damage to white matter, while others report no significant links. Animal studies have indicated potential mechanisms where high-fat, sugary diets could increase amyloid deposits in animal models, though the applicability to humans remains uncertain. The review emphasizes the difficulty in conducting long-term studies that could definitively establish causation due to the complexity of diet and cognitive health.
To enhance understanding, researchers recommend possible strategies like small, controlled trials switching individuals between diets and utilizing technology to monitor food intake. They also suggest public health measures similar to tobacco control, such as taxes on sugary drinks and regulations on food marketing aimed at children. Despite the current findings, researchers maintain that more extensive long-term studies are necessary to clarify the impacts of ultraprocessed foods on memory and cognitive health. The full study was published in the journal Annual Review of Nutrition.