Eating a Mediterranean diet that is rich in nuts and olive oil may help delay cognitive decline in older adults, according to a new study.

In the study, researchers randomly chose about 300 people to follow a Mediterranean diet for four years, and asked 145 people to eat a low-fat diet for the same period. Following a Mediterranean diet means consuming many vegetables and fruits, and eating some seafood, while eating only a little meat and dairy.

In the study, 155 of the people who were on a Mediterranean diet were asked to include one liter of extra virgin olive oil in their diet per week, and 147 people were asked to supplement their diet with 30 grams per day of a mix of walnuts, hazelnuts and almonds.

After four years, researchers compared the cognitive function of the people in each group. The average age of the people in the study was 67.

It turned out that the groups of people who followed the Mediterranean diet experienced an improvement in cognitive function over four years, whereas it declined in the people eating the low-fat diet.

“Our results suggest that in an older population, a Mediterranean diet supplemented with olive oil or nuts may counteract age-related cognitive decline,” the researchers wrote in the study.

Given the lack of effective treatments for people suffering from a decline in cognitive function and dementia, strategies that could delay the onset of these conditions or minimize their effects are needed, they wrote. Although the new results are encouraging, more research is needed to confirm them, the researchers noted.

The researchers also found that the people in the group who followed the Mediterranean diet plus extra nuts experienced significant improvements in memory abilities, compared with those on the low-fat diet. And those who followed the Mediterranean diet with the extra virgin olive oil showed significantly greater improvement in a number of cognitive functions related to working memory, reasoning and attention, compared with the low-fat diet group.

There are a number of mechanisms that may explain the beneficial effect that the Mediterranean diet and the supplementary foods had on cognitive function, the researchers said. For example, it may be that the so-called phenolic compounds, found in both nuts and olive oil, may help counteract the chemical processes in the brain that lead to neurodegeneration.

Dr. Raphael Kellman, an internist in New York City who was not involved in the study, said that the study shows that, when they are consumed, the omega fats in olive oil and nuts play an important role in improving the condition of cell membranes, including those in the brain.

“When you consume an abundance of these types of oils and fats, then you are improving brain function,” which could help prevent neurodegenerative disorders, said Kellman, who also wrote the book “The Microbiome Diet” (Da Capo Press, 2014).

On the other hand, if a person reduces how much of these types of fats they eat, it may have a negative effect on the brain and overall health, he said.

The study also shows that “you need fat — but the issue is what type of fat — not all fat was created equal,” Kellman told Live Science. For example, consuming too much saturated fat could affect cell membranes in a negative way, he said.

“So it is about balance,” he said.

The study was published on May 11 in the journal JAMA Internal Medicine.

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This article originally published at LiveScience here