A diet rich in berries, nuts and green leafy vegetables may help improve memory, but only in women, research suggests.
Following the MIND diet (which stands for Mediterranean Dash Diet for Intervention in Neurodegenerative Delay) was associated with less cognitive decline, a precursor to dementia.
But the same results were not seen for both sexes, suggesting it might only work in women, who are much more likely to suffer from dementia than men.
The researchers analyzed data from 14,145 people with an average age of 64, who were followed for an average of a decade.
A meal plan that follows the MIND diet. An oatmeal breakfast, lentil salad for lunch and a fish pie for dinner.
They completed dietary surveys for a year, and the scientists looked at how closely the foods people ate matched the Mind diet.
One point was awarded for adhering to a diet such as three or more daily servings of whole grains or six or more weekly servings of green leafy vegetables.
They also got one point for consuming four or fewer weekly servings of red meat, one or fewer weekly servings of fast or fried food, and five or fewer weekly servings of cakes and sweets.
The total possible points were 12, according to the findings published in the journal Neurology.
The people were then divided into three groups: the low group had an average diet score of five, the medium group had an average score of seven, and the high group had 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 daily life) developed in 532 people (or 12 percent) in the low-carb diet group during the course of the study.
It also occurred in 617 people (or 11 percent) in the middle group, and in 402 people (or 10 percent) in the high group.
Researchers found a 6 percent decrease in the risk of cognitive decline for female participants who followed the diet more closely, but no decrease in risk for men who did the same.
People who followed the Mind diet more closely also declined less rapidly than those who did not, and this link was stronger among black people than among white people.
Experts said more research was needed to try to understand these differences and acknowledged limitations, such as self-reporting of diet that can lead to inaccuracies.
Study author Dr Russell Sawyer, from the University of Cincinnati in Ohio, said: ‘As the number of people with dementia increases with the ageing population, it is critical to find changes we can make to delay or slow the development of cognitive problems.
‘These findings warrant further study, especially to examine these different impacts between men and women and between white and black 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 problems.’
Previous research has suggested that the Mind diet may protect the brain by reducing oxidative stress and inflammation due to its high levels of vitamins, carotenoids and flavonoids.
Experts say it may also reduce the risk of heart disease, diabetes and some types of cancer.
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.
‘Larger, longer-term studies will be needed to better understand this effect and should be conducted in a more diverse group of people.’