Following the Mind diet – which is rich in leafy vegetables, berries, nuts and beans – could stave off thinking and memory problems, according to new research.
Experts said it was “critical” to find changes that people could make to help prevent conditions such as dementia.
The Mind diet (known as the Mediterranean-Dash Diet Intervention for Neurodegenerative Delay) was created by experts including from the Harvard Chan School of Public Health in the US.
It recommends specific “brain healthy” foods that people should eat and also lists five unhealthy food items to limit.
The healthy items suggested by the diet include: three or more servings a day of whole grains, six or more servings a week of green leafy vegetables, one or more servings a day of other vegetables, five or more servings a week of nuts, four or more portions of beans, two or more servings a week of berries, two or more meals a week of poultry and one or more meals a week of fish.
Olive oil should be the main fat used in the diet while unhealthy items should be avoided or reduced.
This means there should be fewer than five servings a week of pastries and sweets, fewer than four servings a week of red meat, less than one serving a week of cheese and fried foods and less than one tablespoon a day of butter or margarine.
In the latest study, published online in the journal Neurology, experts looked at data for 14,145 people with an average age of 64, who were followed for a decade on average.
Some 70% of those in the study were white and 30% were black and all were asked to fill out questionnaires on their diet over the past year.
Researchers looked at how closely the foods people were eating matched the Mind diet.
People were given one point for each bit of adherence to the diet (such as if they had six or more weekly servings of green leafy vegetables or five or fewer weekly servings of pastries and sweets).
The total points possible was 12.
Experts then divided the people into three groups, with the low group having an average diet score of five, the middle group having an average score of seven and the high group having an average score of nine.
Thinking and memory skills were measured at the beginning and end of the study.
Cognitive impairment (when a person has trouble remembering, learning new things, concentrating, or making decisions that affect everyday life) developed in 532 people (or 12%) in the low diet group during the course of the study.
It also occurred in 617 people (or 11%) of people in the middle group, and in 402 people (or 10%) of people in the high group.
After adjusting for factors such as age, high blood pressure and diabetes, researchers found that people in the high group had a 4% lower risk of cognitive impairment compared to those in the low group.
Women were more likely to see benefit than men, though this needs further study, researchers said.
People who most closely followed the Mind diet also declined less rapidly than those who did not, with this link stronger among black people than white.
Study author Dr Russell Sawyer, from the University of Cincinnati in Ohio and member of the American Academy of Neurology, said: “With the number of people with dementia increasing with the aging population, it’s critical to find changes that we can make to delay or slow down the development of cognitive problems.
“These findings warrant further study, especially to examine these varying impacts among men and women and black and white people, but it’s exciting to consider that people could make some simple changes to their diet and potentially reduce or delay their risk of cognitive issues.”
Previous research has suggested that the Mind diet can protect the brain by reducing oxidative stress and inflammation owing to its high levels of vitamins, carotenoids and flavonoids.
Experts say it may also reduce the risk of heart disease, diabetes and some cancers.
The study was funded by the National Institute of Neurological Disorders and Stroke and the National Institute on Aging.
Dr Jacqui Hanley, head of research at Alzheimer’s Research UK, said: “There is a wealth of evidence that eating a healthy, balanced diet can help protect our brain health. But the benefits of specific diets is less clear.
“This study adds more evidence that a Mediterranean-style diet called the Mind diet – which includes leafy greens, nuts, poultry, fish, and berries – may delay cognitive decline, including memory issues.
“However, without a detailed picture of what’s going on in the brain, we don’t know whether there is a direct link between this diet and a reduced risk of cognitive impairment. Larger and longer-term studies will be needed to understand this effect more and this should be carried out in a more diverse group of people.”