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We’ve long been told that vegetarianism can improve heart health, nutrient intake and digestion while lowering the risk of chronic disease and certain cancers — but some plant-based diets may do more harm than good.
Case in point: A new study in the scientific journal Neurology finds that high-quality, vitamin-rich plant-based diets go a long way in warding off Alzheimer’s disease and related dementias.
But low-quality plant-based diets, heavily reliant on refined carbs and sugars, were hardly neutral for brain health — instead, they actively increased a person’s risk of cognitive disease by 6%.
The prognosis was significantly worse for people who started out eating healthier foods but skewed towards an unhealthy diet over time. For that cohort, dementia risk rose by 25%.
For more than a decade, researchers tracked the diets and cognitive health of nearly 93,000 participants with a range of ethnic backgrounds and an average age of 59 at the outset.
While none of the participants identified as vegan or strictly vegetarian, researchers broke down their diets into three categories: Overall plant-based, healthful plant-based and unhealthful plant-based.
The overall diet generally consisted of more plant-based foods than animal-based products like meats, milk or eggs. The quality of food wasn’t taken into consideration.
The healthful diet was characterized by foods like whole grains, fruits, vegetables, vegetable oils, nuts, legumes, tea and coffee.
And the unhealthful diet was high in refined grains, fruit juices, potatoes and added sugars, per Neuroscience News.
Those who adhered to the healthful diet had a 7% lower risk of dementia, while those in the unhealthful bucket were 6% more likely to develop it.
Changing your diet over time also had a major impact on brain health: Those who adopted a healthier plant-based diet during the 11-year study period had an 11% decrease in risk, whereas those who began eating a higher volume of unhealthy plant-based foods during the study period had a 25% increase in risk.
Song-Yi Park, one of the study’s authors and a researcher at the University of Hawaii at Manoa’s Cancer Center in Honolulu, said these findings help enhance clinical understandings of the benefits — and potential risks — of a diet profile that’s well-beloved by medical professionals and social media influencers alike.
“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,” he said.
Past research has highlighted the connection between diet and brain health, finding that the neural system is sensitive to inflammation caused by spikes in blood sugar.
The refined carbs and sugars so common in the unhealthy plant-based diet can trigger those spikes, helping to explain the higher risk of dementia.
Healthy plants, however, are brain food. Many fruits and vegetables are high in antioxidants, which protect neurons from toxins and help to cut down on inflammation.
It’s not just vegetables that should get all the glory. Protein intake — including animal protein — has been linked to better cognitive health outcomes as we age, too.
Per a 2022 Harvard study, swapping in a small amount of animal protein for carbohydrates led to an 11% lower risk for developing dementia. And swapping in the same amount of plant protein for carbs resulted in a 26% lower risk.
The researchers especially raved about the protective qualities of beans and legumes like peas and lima beans, which were associated with a 28% “lower risk of cognitive decline for every additional three servings per week.”
Still, other studies show mixed results about the impact of protein on the aging brain.
But when it comes to eating plants, one thing is clear: Sowing healthy habits now will pay off later.
