Food for Brain Higher-Quality Plant-Based Diets Linked to Lower Dementia Risk

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A plant-based diet may help lower the risk of Alzheimer’s disease and related dementias, but quality appears to make the difference. A large long-term study suggests that diets rich in whole grains, fruits, vegetables, nuts and legumes are associated with lower dementia risk, while less healthful plant-based eating patterns may raise it.

Eating a higher quality plant-based diet is associated with a lower risk of Alzheimer’s disease and other related dementias compared to eating a lower quality plant-based diet, according to a study published April 8, 2026, in Neurology, the medical journal of the American Academy of Neurology. While the study shows an association based on observations, it does not prove that a higher quality plant-based diet causes a lower risk of dementia.

Researchers looked at three plant-based diets. The overall plant-based diet prioritizes eating more plant foods than animal products like meat, milk and eggs, without looking at quality. The healthful plant-based diet prioritizes healthy plant foods like whole grains, fruits, vegetables, vegetable oils, nuts, legumes and tea and coffee. The unhealthful plant-based diet includes less healthy plant foods like refined grains, fruit juices, potatoes and added sugars. Researchers did not look at 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.”

The study involved 92,849 people with an average age of 59 at the start of the study. It included African American, Japanese American, Latino, Native Hawaiian and white participants. They were followed for an average of 11 years. During that time, 21,478 people developed Alzheimer’s disease or another related dementia.

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Participants completed food questionnaires at the start of the study. Researchers determined how well people’s diets resembled the overall plant-based diet, the healthful plant-based diet and the unhealthful plant-based diet, by reviewing how many healthy and less healthy plant foods they ate, as well as animal fats, meat, dairy, eggs, fish and seafood. Participants were each given three scores based on how closely they followed the three plant-based diets.

Researchers then ranked the participants into five subgroups for each of the three diet scores.

After adjusting for factors like age, physical activity and diabetes, researchers found that when comparing people based on their score for the overall plant-based diet, the top subgroup who ate the most plant foods had a 12% lower risk of dementia compared to the lowest subgroup. When people were compared based on their score for the healthful plant-based diet, the top subgroup had a 7% lower risk compared to the lowest subgroup. And when compared based on their score for the unhealthful plant-based diet, the top subgroup who ate the most unhealthy plant foods had a 6% higher risk of dementia than the lowest subgroup.

Among a smaller group of 45,065 participants who reported their diet again after 10 years, 8,360 participants later developed dementia. Researchers looked at diet changes over time. When compared to people whose diets didn’t change, people whose diets changed the most toward following an unhealthful diet had a 25% higher risk of dementia while those whose diets changed the most away from following an unhealthful diet 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.”

A limitation of the study was that researchers evaluated the diets based on food questionnaires completed by participants, but participants may not remember every detail of their diets accurately.

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