People who eat diets rich in green leafy vegetables as well as other vegetables, fruits, whole grains, olive oil, beans, nuts and fish may have fewer amyloid plaques and tau tangles in their brains — signs of Alzheimer’s disease — than people who don’t eat such diets, according to a study published in the March 8, 2023, online issue of Neurology®the medical journal of the American Academy of Neurology.
The study looked at how closely people followed MIND and the Mediterranean diet. Although similar, the Mediterranean diet recommends vegetables, fruit and three or more servings of fish per week, while the MIND diet prioritizes green leafy vegetables such as spinach, kale and collard greens along with other vegetables. The MIND diet also prioritizes berries over other fruits and recommends one or more servings of fish per week. Both MIND and the Mediterranean diet recommend small amounts of wine.
While this study shows an association of regular consumption of these diets with fewer Alzheimer’s plaques and tangles, it does not establish a cause-and-effect relationship.
“These results are exciting — improving people’s diets in just one area — such as eating more than six servings of green leafy vegetables a week or not eating fried foods — was associated with fewer amyloid plaques in the brain similar to about four years younger,” said study author Puja Agarwal, PhD, of RUSH University in Chicago. “Although our research did not prove that a healthy diet resulted in fewer amyloid plaque deposits in the brain, also known as a marker of Alzheimer’s disease, we know there is a connection, and following MIND and the Mediterranean diet may be a way to which people can improve their brain health and protect cognition as they age.”
The study involved 581 people with an average age of 84 at the time of the diet assessment who agreed to donate their brains upon death to advance dementia research. Participants completed annual questionnaires asking how much they consumed food in various categories.
Participants died an average of seven years after the study began. Just before death, 39% of participants had been diagnosed with dementia. When examined postmortem, 66% met criteria for Alzheimer’s disease.
At autopsy, the researchers examined the participants’ brains to determine the amounts of amyloid plaques and tau tangles. Both are found in the brains of people with Alzheimer’s disease, but may also be found in the brains of older people with normal cognitive function. The researchers then reviewed the food questionnaires collected during the follow-up and ranked the quality of the diet for each individual.
For the Mediterranean diet there were 11 food categories. Participants were given a score from zero to 55, with higher scores if they followed a diet in these categories: whole grains, fruits, vegetables, legumes, olive oil, fish, and potatoes. They got lower scores if they ate red meat, poultry and full-fat dairy products.
For the MIND diet there were 15 categories. Participants were given a score from zero to 15, with one point each for 10 brain-healthy food groups, including green leafy vegetables, other vegetables, nuts, berries, beans, whole grains, fish, poultry, olive oil and wine. They lost one point if they ate more foods than recommended in five unhealthy food groups, including red meat, butter and margarine, cheese, pastries and sweets, and fried and fast food.
The researchers then divided the participants into three groups for each diet and compared those in the highest groups with those in the lowest groups. For the Mediterranean diet, subjects in the highest group had an average score of 35 while subjects in the lowest had an average score of 26. For the MIND diet, the highest group had an average score of 9 while the lowest group had an average score of 6.
After adjusting for age at death, sex, education, total calorie intake and whether people had a gene linked to a higher risk of Alzheimer’s disease, the researchers found that people who scored higher on adherence of the Mediterranean diet had average amounts of plaque and tangles in their brains. similar to being 18 years younger than the people who scored the lowest. The researchers also found that people who scored higher on adherence to the MIND diet had an average amount of plaque and tangles similar to being 12 years younger than those who scored lower.
A MIND diet score one point higher corresponded to typical amounts of plaque in participants who were 4.25 years younger in age.
When they looked at the individual components of the diet, the researchers found that people who ate the highest amounts of green leafy vegetables, or seven or more servings per week, had amounts of plaque in their brains equivalent to being almost 19 years younger than people who they ate the least, with one or fewer servings per week.
“Our finding that eating more green leafy vegetables alone is associated with fewer signs of Alzheimer’s disease in the brain is interesting enough for people to consider adding more of these vegetables to their diet,” Agarwal said. “Future studies are needed to further substantiate our findings.”
A limitation of the study was that the participants were mostly white, non-Hispanic, and older, so the results may not be generalizable to other populations.
The study was funded by the National Institutes of Health.