The Surprising Diet That Could Raise Your Dementia Risk by 25%, According to a New Study

Plus, the diet that could significantly lower your risk.

Reviewed by Dietitian Jessica Ball, M.S., RD

Key Points

• A nutrient-dense plant-based diet may lower dementia risk, while unhealthy plant foods increase it.
• Whole grains, nuts, and vegetables support brain health; added sugars and refined grains raise dementia risk.
• Moderate animal products, like eggs, may offer protective brain benefits when paired with whole plant foods.

People have long recognized that eating a diet rich in plants can benefit your heart health. Researchers are now looking at how these same dietary choices affect the brain, specifically regarding how doing so may be linked to a reduced risk of Alzheimer’s disease and related dementias. Because heart conditions and brain health share common pathways, diets that protect your cardiovascular system might also protect your cognitive function.

However, simply avoiding meat does not guarantee a healthy diet. Past research often grouped all vegetarian or vegan diets together without looking at the actual nutritional value of the foods consumed. A diet full of sugar-sweetened sodas and refined grains is technically plant-based, but it can lack the nutrients your brain needs.

To better understand this dynamic, researchers recently conducted a large-scale study to see exactly how the quality of plant-based foods affects dementia risk over time. The results were published in Neurologythe medical journal of the American Academy of Neurology.

How Was the Study Conducted?

To explore the connection between diet and brain health, researchers analyzed data from the Multiethnic Cohort Study. This massive project tracked more than 92,000 Medicare beneficiaries between the ages of 45 and 75. The participants lived primarily in Hawaii and California and represented five diverse backgrounds.

Researchers gathered dietary information using comprehensive food questionnaires at the start of the study and again 10 years later. To evaluate the diets, the research team categorized food intake using three distinct scoring systems based on 16 food groups:

1. Overall Plant-based Diet Index (PDI): This index measures the general intake of all plant foods, without considering their nutritional quality.
2. Healthful Plant-based Diet Index (hPDI): This index emphasizes the consumption of nutrient-dense foods like whole grains, fruits, vegetables, vegetable oils, nuts, legumes and tea or coffee.
3. Unhealthful Plant-based Diet Index (uPDI): This index focuses on tracking the consumption of less nutritious items like refined grains, fried potatoes, fruit juices and added sugars.

For all three indices, consuming animal products resulted in lower scores. By comparing these diet scores against Medicare claims for dementia diagnoses over an average of almost 11 years, researchers could map how food quality relates to long-term brain health.

What Did the Study Find?

The findings reveal a clear link between the quality of a plant-based diet and the risk of developing dementia. Participants who ate the highest amount of plant-based foods overall (highest PDI) had a 12% lower risk of developing dementia compared to those who ate the least. Those who closely followed a healthy plant-based diet (highest hPDI) experienced a 7% reduced risk. Conversely, people who consumed the highest amounts of unhealthy plant-based foods (highest uPDI) faced a 6% increased risk.

The study also tracked how changing your diet over a 10-year period impacts your brain. Participants who experienced a large drop in their “healthy” plant food intake saw their dementia risk rise by 17%. Meanwhile, those who sharply increased their consumption of unhealthy plant foods experienced a 25% jump in risk.

When analyzing specific food groups, researchers noted that a large decrease in the consumption of whole grains, vegetable oils, nuts and tea or coffee was associated with an 11% to 15% higher risk. Eating more added sugars was directly linked to a 12% higher risk. Interestingly, decreasing egg consumption was also associated with a 12% higher risk, indicating that certain animal products may still offer protective benefits.

The researchers observed some variations among racial and ethnic groups. The increased risk associated with adopting a highly unhealthful plant-based diet was present in almost all groups, but it was strongest among Native Hawaiian participants and not statistically significant for the Latino group.

Limitations

While this study offers valuable insights, there are some limitations to consider. First, the researchers relied on Medicare billing claims to identify dementia cases. While these records are generally reliable, they might miss some diagnoses or fail to capture the exact subtype of dementia perfectly.

Second, the study used food frequency questionnaires to track dietary habits. This method requires participants to remember and estimate what they ate over the past year, which naturally introduces some memory errors. Third, even though the researchers accounted for many variables like physical activity, education and medical history, other unmeasured lifestyle factors could still influence the results. Finally, because the study focused on specific groups in particular geographic areas, the exact percentages might not apply to every population.

How Does This Apply to Real Life?

These findings demonstrate that adopting a “plant-based” or “vegetarian” label does not automatically protect your brain. You can eat a diet entirely free of animal products but still opt for mostly refined carbohydrates, sugar-sweetened drinks and other ultra-processed foods. The data clearly shows that eating these unhealthy plant foods is associated with a higher risk of cognitive decline.

To support your brain health, you should focus heavily on food quality and choose nutrient-dense options. You do not need to eliminate all animal products to see benefits. Instead, prioritize whole plant foods in your daily meals. For example, swap a refined white bagel with jelly for a bowl of oatmeal topped with walnuts and berries to help include more nutrient-dense plant foods. The study suggests that making these positive dietary shifts, even in middle to late adulthood, may lower your risk of dementia.

Our Expert Take

A new study published in Neurology highlights that the quality of your plant-based diet may have a profound impact on dementia prevention. The data shows that adhering to a healthful plant-based diet is linked to a reduced risk of Alzheimer’s disease and related dementias, while consuming heavily processed, unhealthful plant foods increases that risk by up to 25% over a decade.

You can still include moderate amounts of healthy animal products in your diet, as the data noted a potential protective association with foods like eggs. But we recommend you opt for lean choices and pair them with other nutrient-dense foods like whole grains and vegetables. By prioritizing whole foods over strict dietary labels, you can build a sustainable eating pattern that supports your brain well into the future.