• Posted April 10, 2026

Your Brain Cares If Your Plant-Based Diet Is Unhealthy, Researchers Report

The quality of your plant-based diet could either help or harm your aging brain.

Following a healthy plant-based diet in middle age appears to lower a person’s risk of Alzheimer’s disease and other forms of dementia, researchers reported April 8 in the journal Neurology.

The keyword is healthy — folks in the study who ate unhealthy plant-based foods like French fries and fruit juices actually had a higher risk of Alzheimer’s and 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,” lead researcher Song-Yi Park, a University of Hawaii epidemiologist, said in a news release.

The study doesn't prove that a plant-based diet prevents dementias, only that there's a link. But switching up your diet for better or worse can lower or increase your Alzheimer’s risk, researchers found.

“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.

For the new study, researchers recruited nearly 93,000 people living in Hawaii and California, including African American, Japanese American, Latino, Native Hawaiian and white participants.

Participants completed a food-based questionnaire, and from that data researchers tracked three eating patterns:

• An average plant-based diet prioritized eating more veggies and fruits than animal products like meat, milk and eggs.

• A healthy plant-based diet prioritzed whole grains, fruits, vegetables, vegetable oils, nuts, legumes, tea and coffee.

• An unhealthy plant-based diet included lots of added sugars, fruit juices, refined grains and fast-food or processed potato products like fries or chips.

“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,” Park said.

Participants were, on average, 59 years old when the study began, and they were followed for an average 11 years. During that time, nearly 21,500 developed Alzheimer’s disease or dementia.

Overall, people who ate the most plant-based foods had a 12% lower risk of dementia compared to those who ate the least.

Researchers also found that those who consumed the healthiest plant-based foods had a 7% lower risk of dementia, while those who ate the most unhealthy plant foods had a 6% higher risk.

A smaller group of around 45,000 participants completed a second round of food questionnaires after 10 years.

Those whose diets had become healthier had an 11% lower risk of dementia, while those whose diets had gotten worse had a 25% higher risk, the study found.

In general, plant-based diets can lower cholesterol levels and promote overall healthier aging, researchers said in background notes. They’re also rich in vitamins, minerals and fiber.

However, unhealthy foods like fruit juice or refined grains can raise blood sugar levels, increasing a person’s risk of diabetes.

“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,” Park said.

More information

Harvard Medical School has more on the best plant-based diets.

SOURCES: American Academy of Neurology, news release, April 8, 2026; Neurology, April 8, 2026