Eating leafy greens, nuts, and fish, among other food items typical of the Mediterranean Diet, was found to be associated in elderly brains with fewer plaques thought to cause Alzheimer's.

It is believed that the disease is caused by a build-up of tau proteins called amyloid-beta, which block neuron connections.

Scientists at the American Academy of Neurology have found an association between the diet and reduced amounts of these tau proteins.

The scientist looked at how closely 561 adults with an average age of 84 followed the so-called Mediterranean Diet or the MIND Diet, which both emphasize more fish than red meat, and more vegetables than fruit. The former calls for a lot of olive oil, while the latter diverges with a call specifically for berries over other fruits.

The participants died an average of seven years after the start of the study. Right before death, 39% of participants had been diagnosed with dementia. When examined after death, 66% met the criteria for Alzheimer's disease.

At autopsy, researchers examined participants' brains to determine the amounts of amyloid plaques and tau tangles. Researchers then looked back at a series of food questionnaires regarding adherence to the two diets which were collected over years and ranked the quality of the diet for each person.

For the Mediterranean diet, there were 11 food categories. Participants were given a score of zero to 55, with higher scores if they adhered to the diet in these categories: whole grain cereals, fruits, vegetables, legumes, olive oil, fish, and potatoes. They were given 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 of 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 a point if they ate foods more than recommended in five unhealthy food groups, including red meats, butter and margarine, cheese, pastries and sweets, and fried and fast food.

Researchers then divided participants into three groups for each diet and compared those in the highest groups to those in the lowest groups.

After adjusting for age at death, sex, education, total calorie intake, and whether people had a gene linked to a greater risk of Alzheimer's disease, researchers found people who scored highest for adhering to the Mediterranean diet had average plaque and tangle amounts in their brains similar to being 18 years younger than people who scored lowest.

Researchers also found people who scored highest for adhering to the MIND diet had average plaque and tangle amounts similar to being 12 years younger than those who scored lowest.

A MIND diet score one point higher corresponded to typical plaque amounts of participants who were 4.25 years younger in age.

When looking at single diet components, researchers found people who ate the highest amounts of green leafy vegetables, or seven or more servings per week, had plaque amounts in their brains corresponding to being almost 19 years younger than people who ate the fewest, with one or fewer servings per week.

"These results are exciting—improvement in people's diets in just one area—such as eating more than six servings of green leafy vegetables per week, or not eating fried foods—was associated with fewer amyloid plaques in the brain similar to being about four years younger," said study author Puja Agarwal, Ph.D., of RUSH University in Chicago.

"While our research doesn't prove that a healthy diet resulted in fewer brain deposits of amyloid plaques, also known as an indicator of Alzheimer's disease, we know there is a relationship and following the MIND and Mediterranean diets may be one way that people can improve their brain health and protect cognition as they age."

However, the data is not conclusive and a cause-and-effect relationship was not established. Self-reporting questionnaires are an inexact means of gathering evidence.

The Mediterranean Diet is a difficult scholarly tool. The idea is that long lifespans and lower incidences of cardiovascular disease, stroke, and cancer are seen in Mediterranean populations, but more than any dietary component, these things are determined by income level—with richer countries having better outcomes, and poorer countries having worse ones.

Also, the Mediterranean Dieters in this study were marked down for the consumption of full-fat dairy and red meat—which the Mediterranean nations of Italy, France, and Spain eat at higher rates than almost anywhere else in Europe. The problem for the scientists is that these countries have some of the highest life expectancies on the continent, despite their love affair with cured meats and cheeses, not to mention pizza and pasta.

What's likely to do with the improvements if Alzheimer's markers is that adhering to diets that emphasize certain foods requires cutting out the obviously unhealthy effects of fried and ultra-processed foods.

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