Plant-food rich diets might have a lower risk of Alzheimer’s disease, but the quality of the diet is crucial.
Adults who eat a healthy plant-based diet — focusing on whole, minimally processed foods such as vegetables, fruits, whole grains, legumes, nuts, and seeds — might have a lower risk of developing Alzheimer’s disease and other dementias, even if they start the diet later in life.
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The study published in Neurology analysed data from nearly 93,000 adults with an average age of 59. Researchers tracked their diets and health outcomes over more than a decade.
Rather than focusing on vegetarian or vegan diets, the researchers distinguished between three patterns: an overall plant-based diet, a healthy diet rich in whole foods, and a less healthy one high in refined and processed products.
Among 92,849 participants followed for 11 years, 21,478 developed Alzheimer’s disease or another dementia.
Diet quality plays an important role
The results show a link rather than a direct cause-and-effect relationship, and they suggest that not all plant-based diets offer the same benefits.
Participants who consumed the highest amount of plant foods overall had a 12% lower risk of dementia compared to those who ate the least.
But when diet quality was taken into account, the difference became clearer. Those following the healthiest plant-based diets had a 7% lower risk, while those eating the most unhealthy plant-based foods had a 6% higher risk.
"Plant-based diets have been shown to reduce the risk of conditions like diabetes and high blood pressure, but less is known about dementia," said study author Song-Yi Park of the University of Hawaii. "Our study shows that the quality of those diets is crucial."
Diet changes matter, even later in life
The study also examined how dietary habits evolved in a subgroup of 45,065 participants. Of this total, 8,360 participants in this group later developed dementia.
They found that those whose diets shifted towards more unhealthy plant-based foods over 10 years had a 25% higher risk of dementia, while people who improved their diets saw their risk fall by 11%.
The data indicate that diet changes later in life can still be linked to dementia risk. According to the researchers, adopting a healthier plant-based diet after the age of 60 was also associated with a reduced risk of dementia.
The study relied on self-reported food questionnaires, which can be prone to inaccuracies. Participants may not recall their diets precisely, potentially affecting the results.
However, the large sample size and long follow-up period strengthen the findings.
The results align with previous research linking dietary patterns such as the Mediterranean or MIND diets to better cognitive health, particularly when they emphasise whole, minimally processed foods.
Experts have cautioned that this latest study is observational. That means it cannot prove that diet alone prevents dementia, and other factors, such as physical activity, education or overall lifestyle, may also play a role.
