People who ate a higher quality plant-based diet had a lower risk of Alzheimer's disease and related dementias than those 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. The distinction matters: simply swapping animal foods for plant foods was not the deciding factor. What separated the groups was which plant foods people ate.
Researchers assessed three patterns. An overall plant-based diet favored plant foods over meat, milk and eggs without regard to quality. A healthful plant-based diet emphasized whole grains, fruits, vegetables, vegetable oils, nuts, legumes, tea and coffee. An unhealthful plant-based diet leaned on refined grains, fruit juices, potatoes and added sugars. Vegetarian and vegan diets were not examined. The study followed 92,849 people with an average age of 59 for about 11 years, drawing on African American, Japanese American, Latino, Native Hawaiian and white participants. During follow-up, 21,478 developed Alzheimer's disease or another dementia.
"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," said study author Song-Yi Park, PhD, of the University of Hawaii at Manoa's Cancer Center in Honolulu. Park noted that plant-based eating has already been tied to lower risk of diabetes and high blood pressure, but its relationship to dementia has been less clear.
This was an observational study, so it shows an association rather than proving that a higher quality plant-based diet causes lower dementia risk. Still, the size of the cohort and the range of ethnic groups included give the finding unusual reach, and the emphasis on food quality offers researchers a more specific target than the broad label "plant-based" has provided so far.