A large, long-term study suggests that the quality of a plant-based diet may play a meaningful role in the risk of Alzheimer’s disease and related dementias. Researchers found that diets built around whole plant foods like vegetables, fruits and legumes were associated with a lower risk, while diets higher in refined carbohydrates and added sugars were linked to a higher risk.
The findings, published in Neurology, are based on data from nearly 93,000 adults followed for more than a decade. Importantly, the study does not show that diet directly causes or prevents dementia, but it adds to growing evidence that overall eating patterns may influence long-term brain health.
Researchers evaluated three types of plant-based diets. One simply emphasized eating more plant foods than animal products, regardless of quality. A second focused on higher-quality plant foods such as whole grains, vegetables, fruits, nuts, legumes, vegetable oils, tea and coffee. A third reflected lower-quality plant-based eating patterns, including refined grains, fruit juices and added sugars.
“Plant-based diets have been shown to be beneficial in reducing the risk of diseases like diabetes and high blood pressure, but less is known about the risk of Alzheimer’s disease and other dementias,” said Song-Yi Park, PhD, of the University of Hawaii at Manoa’s Cancer Center in Honolulu. “Our study found that the quality of a plant-based diet mattered, with a higher quality diet associated with a reduced risk, and a lower quality diet associated with an increased risk.”
Compared to those eating the least plant foods, participants with the highest intake had a 12% lower risk of dementia. When researchers looked more closely at diet quality, those following the healthiest plant-based patterns had a 7% lower risk, while those consuming the most lower-quality plant foods had a 6% higher risk.
The study also tracked how diets changed over time in a subset of participants. People whose diets shifted toward more refined, lower-quality plant foods had a 25% higher risk of dementia, while those who moved toward healthier plant-based patterns had an 11% lower risk.
“We found that adopting a plant-based diet, even starting at an older age, and refraining from low-quality plant-based diets were associated with a lower risk of Alzheimer’s and other dementias,” Park said.
The results highlight a key distinction that often gets lost in nutrition conversations. Simply eating more plant-based foods does not automatically mean a healthier diet. Foods like refined grains, sugary drinks and heavily processed snacks can still dominate a plant-based pattern.
At the same time, the study has limitations. Diet was measured using self-reported questionnaires, which can be imprecise, and the observational design means other lifestyle factors may also play a role. Still, the large sample size, long follow-up and diverse participant group strengthen confidence in the findings.
The study was supported by the National Institute on Aging and the National Cancer Institute, both part of the National Institutes of Health.