"In this important study, researchers showed that it's possible to not only improve cognitive function -- most specifically memory -- but also reduce risk for Alzheimer's disease pathology," said Isaacson, who was not involved in the study.

"For every point of higher compliance with the diet, people had one extra year less of brain aging. That is striking," Isaacson added. "Most people are unaware that it's possible to take control of your brain health, yet this study shows us just that."

What is the Mediterranean diet?

Forget lasagna, pizza, spanakopita and lamb souvlaki -- they are not on the daily menu of those who live by the Mediterranean seaside.

The true diet is simple, plant-based cooking, with the majority of each meal focused on fruits and vegetables, whole grains, beans and seeds, with a few nuts and a heavy emphasis on extra-virgin olive oil. Fats other than olive oil, such as butter, are consumed rarely, if at all. And say goodbye to refined sugar or flour.

Meat can make a rare appearance, but usually only to flavor a dish. Instead, meals may include eggs, dairy and poultry, but in much smaller portions than in the traditional Western diet. However, fish, which are full of brain-boosting omega-3's, are a staple.

Brain Scans and Spinal Fluid

The study, published Wednesday in Neurology, the medical journal of the American Academy of Neurology, examined 343 people at high risk of developing Alzheimer's and compared them to 169 cognitively normal subjects.

First, researchers tested each person's cognitive skills, including language, memory and executive function, and used brain scans to measure brain volume. Spinal fluid from 226 participants was also tested for amyloid and tau protein biomarkers.

Then people were asked how well they were following the Mediterranean diet. After adjusting for factors like age, sex and education, the study found that people who did not follow the diet closely had more signs of amyloid and tau buildup in their spinal fluid than those who did adhere to the diet.

In addition, for each point a person lost on failing to follow the Mediterranean diet, brain scans revealed one additional year of brain aging in areas associated Alzheimer's, such as the hippocampus.

"These results add to the body of evidence that show what you eat may influence your memory skills later on," said study author Tommaso Ballarini, a postdoctoral fellow at the German Center for Neurodegenerative Diseases in Bonn, Germany, in a statement.

"One unanswered question remains: Why exactly does the Mediterranean diet protect against Alzheimer's?" said Isaacson, who is also a trustee of the McKnight Brain Research Foundation.

While further studies are needed, it's likely that a combination of factors are working "synergistically together," he added, "such as reducing inflammation, increasing protective antioxidants, and supplying the brain with brain-healthy fats from fish high in omega-3s -- like wild salmon -- as well as monounsaturated fats from extra-virgin olive oil."

A Growing Connection

This isn't the first research to find a link between brain health and the Mediterranean diet or one of its plant-based cousins.

A study of nearly 6,000 healthy older Americans with an average age of 68 found those who followed the Mediterranean or the similar MIND diet lowered their risk of dementia by a third.

Short for Mediterranean-DASH Intervention for Neurodegenerative Delay, MIND focuses on eating at least six servings a week of green leafy vegetables such as spinach or kale, and at least one serving a day of another vegetable.

"Eating a healthy plant-based diet is associated with better cognitive function and around 30% to 35% lower risk of cognitive impairment during aging," lead author Claire McEvoy, assistant professor at Queen's University Belfast, told CNN when the study published.

"In this study, while the Mediterranean diet overall decreased risk, the strongest factor to really move the needle was regular fish consumption," Isaacson said.

The more people stayed on those diets, McEvoy said, the better they functioned cognitively.

Those who marginally followed the diet also benefited, but by a much smaller margin. These study participants were 18% less likely to exhibit signs of cognitive impairment.

How to Start the Mediterranean Diet

Want to jump on the Mediterranean diet bandwagon and protect your brain as well as your eyes?

Experts say the easiest way to start is to replace one thing at a time. For example, replace refined grains with whole grains by choosing whole wheat bread and pasta and swapping white rice with brown or wild rice.

Cook one meal each week based on beans, whole grains and vegetables, using herbs and spices to add punch. No meat allowed. When one night a week is a breeze, add two, and build your nonmeat meals from there.

On the Mediterranean diet, cheese and yogurt show up daily to weekly, in moderate portions; chicken and eggs are OK on occasion, but the use of other meats and sweets is very limited.

When you eat meat, have small amounts. For a main course, that means no more than 3 ounces of chicken or lean meat. Better yet: Use small pieces of chicken or slices of lean meat to flavor a veggie-based meal, such as a stir-fry.

Eat a lot of veggies and use all kinds and colors to get the broadest range of nutrients, phytochemicals and fiber. Cook, roast or garnish them with herbs and a bit of extra-virgin olive oil.

If fish is the king, olive oil is the queen in the Mediterranean diet -- stay away from coconut and palm oil, experts say. Even though they are plant-based, those oils are high in saturated fats that will raise bad cholesterol.

Adopting the fare of the sunny region will also help with healthy weight loss, while reducing the risk for diabetes, depression, high cholesterol, heart disease, stroke and some cancers.
Easing into the Mediterranean diet means all those benefits and a healthier mind, too? That's definitely a no-brainer!

Fish is king in the Mediterranean diet, and is eaten at least twice a week.
"Fatty fish like wild salmon, sardines, albacore tuna, lake trout and mackerel are loaded with brain-healthy omega-3 fatty acids, which nourish the brain cells," Isaacson said.
Focus on fruits, vegetables, grains, nuts and seeds. Add whole grains and fruit to every meal, but use nuts and seeds as a garnish or small snack due to their high calorie and fat content.