Researchers found that not all plant-based diets are equal when it comes to dementia risk. The findings hint that certain long-term dietary patterns may subtly shape brain health as people age.

A higher quality plant-based diet may be linked to a lower risk of Alzheimer’s disease and related dementias, according to a study published in Neurology, the medical journal of the American Academy of Neurology. The research identified an association, but it did not prove that healthier plant-based eating directly prevents dementia.

Researchers evaluated three types of plant-based diets. The overall plant-based diet focused on eating more plant foods than animal products such as meat, milk, and eggs, regardless of nutritional quality. The healthful plant-based diet emphasized foods such as whole grains, fruits, vegetables, vegetable oils, nuts, legumes, tea, and coffee. The unhealthful plant-based diet included foods like refined grains, fruit juices, potatoes, and added sugars. The study did not examine vegetarian or vegan diets.

“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 study author 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.”

Comparing Healthy and Unhealthy Plant-Based Diets

The study followed 92,849 adults with an average starting age of 59. Participants included African American, Japanese American, Latino, Native Hawaiian, and white adults. Over an average follow-up period of 11 years, 21,478 participants developed Alzheimer’s disease or another form of dementia.

At the beginning of the study, participants completed food questionnaires. Researchers analyzed how closely each person’s eating habits matched the overall, healthful, and unhealthful plant-based diet patterns. The analysis included healthy and less healthy plant foods, along with animal fats, meat, dairy, eggs, fish, and seafood. Each participant received three separate diet scores.

Researchers then divided participants into five groups based on their scores for each diet pattern.

How Researchers Measured Diet Quality

After accounting for factors such as age, physical activity, and diabetes, researchers found that participants in the highest group for the overall plant-based diet had a 12% lower risk of dementia compared to those in the lowest group.

People with the highest scores for the healthful plant-based diet had a 7% lower risk of dementia than those with the lowest scores. In contrast, participants who consumed the highest amounts of unhealthy plant-based foods had a 6% higher risk of dementia compared to those who consumed the least.

Healthy Plant Foods Associated With Reduced Dementia Risk

Researchers also examined a smaller group of 45,065 participants who reported their diets again after 10 years. Among them, 8,360 later developed dementia. The study found that people whose diets shifted most toward unhealthy plant-based foods had a 25% higher risk of dementia compared to those whose diets stayed relatively stable. Meanwhile, participants who moved away from unhealthy plant-based eating 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,” said Park. “Our findings highlight that it is important not only to follow a plant-based diet but also to ensure that the diet is of high quality.”

One limitation of the study was that dietary information came from self-reported food questionnaires, which may not always accurately reflect what participants ate.