A Diet’s Quality, Not Just Its Plant Base, Linked to Dementia Risk
A new study suggests that while plant-based diets are often associated with better health, the specific quality of the foods consumed significantly influences the risk of developing Alzheimer’s disease and other dementias.
A study published on April 8, 2026, in the journal Neurology reports an association between the quality of a plant-based diet and the risk of developing Alzheimer's disease and other dementias. The research, involving nearly 93,000 adults, found that higher consumption of healthful plant-based foods was associated with a lower risk, while a diet high in unhealthful plant-based foods was associated with a higher risk. The authors emphasize that the study demonstrates an association, not a causal relationship.
Study Overview and Methodology
The research was led by Dr. Song-Yi Park from the University of Hawaii at Manoa's Cancer Center. The research team analyzed data from 92,849 participants from a diverse cohort that included African American, Japanese American, Latino, Native Hawaiian, and white individuals. At the start of the study, the average age of participants was 59. They were followed for an average of 11 years, during which 21,478 participants developed Alzheimer's disease or another dementia.
At the study's outset, participants completed food questionnaires. Researchers used this data to assess adherence to three dietary patterns:
- Overall Plant-Based Diet: Prioritizing plant foods over animal products without focusing on food quality.
- Healthful Plant-Based Diet: Emphasizing nutrient-dense foods such as whole grains, fruits, vegetables, vegetable oils, nuts, legumes, tea, and coffee.
- Unhealthful Plant-Based Diet: Featuring foods like refined grains, fruit juices, potatoes, and added sugars.
Participants were categorized into subgroups based on their adherence scores for each diet type. The study did not specifically examine vegetarian or vegan diets.
Key Findings
After adjusting for variables such as age, physical activity, and diabetes, researchers observed the following risk associations:
- Overall Plant-Based Diet: The subgroup with the highest adherence showed a 12% lower risk of dementia compared to the lowest adherence subgroup.
- Healthful Plant-Based Diet: The subgroup with the highest adherence showed a 7% lower risk of dementia compared to the lowest adherence subgroup.
- Unhealthful Plant-Based Diet: The subgroup with the highest consumption of unhealthy plant foods showed a 6% higher risk of dementia compared to the lowest consumption subgroup.
Long-Term Dietary Changes
Among a smaller subset of 45,065 participants who provided follow-up diet information after 10 years, 8,360 later developed dementia. Analysis of dietary shifts over time indicated:
- Participants whose diets shifted significantly towards an unhealthful pattern had a 25% higher risk of dementia.
- Participants whose diets shifted away from an unhealthful pattern showed an 11% lower risk.
Interpretation and Limitations
Dr. Park stated that while plant-based diets are known to be associated with a reduced risk for conditions like diabetes and high blood pressure, their association with Alzheimer's and other dementias has been less understood. The study's findings indicate that the quality of a plant-based diet was a factor in the observed associations.
"The study demonstrates an association and does not establish that diet directly prevents dementia."
The researchers noted that a key limitation acknowledged by the authors was the reliance on participant-completed food questionnaires, which may be subject to recall inaccuracies.
An additional observational study by researchers at the University of Ljubljana and Karolinska Institutet also examined diet quality and brain health. Its lead author, Anja Mrhar, stated that while the findings are consistent with general healthy eating advice for older adults, they cannot prove that changing diet prevents dementia.
The study received support from the National Institute on Aging and the National Cancer Institute at the National Institutes of Health.