Following a Mediterranean diet rich in fruits, vegetables, legumes, whole grains, fish and healthy fats may preserve a more youthful brain in old age, a U.S. study suggests.

Previous research has connected a Mediterranean diet to a reduced risk of developing Alzheimer's disease and other degenerative brain conditions, noted lead study author Yian Gu of Columbia University in New York.

For the current study, researchers focused on elderly people with normal cognitive function to see if the diet might also be tied to losing fewer brain cells due to aging, Gu said by email.

"Among cognitively healthy older adults, we were able to detect an association between higher adherence to a Mediterranean type diet and better brain measures," Yu said.

To understand the relationship between the diet and brain health, Yu and colleagues reviewed surveys that 674 elderly people completed about their eating habits and then examined magnetic resonance imaging (MRI) scans of their brains.

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Compared to the people who didn't regularly follow many aspects of the Mediterranean diet, the participants who adhered to this way of eating more often had larger total brain volume, as well as more gray and white matter.

Higher fish intake and lower meat consumption, one aspect of a Mediterranean diet, was tied to larger total gray matter volume on the brain scans.

Eating less meat was also independently associated with larger total brain volume.

Overall, the difference in brain volume between the people who followed a Mediterranean diet and those who didn't was similar to the effect of five years of aging, the researchers conclude in the journal Neurology.

One limitation of the study is that it can't show whether the diet actually causes less brain atrophy over time, the authors acknowledge. For instance, it's also possible that the effect might operate in the opposite direction, with differences in brain structure resulting in behavioral differences that include dietary habits.

It's also hard to separate the effect of eating more fish from the impact of consuming less meat, noted Dr. Victor Henderson, a neurology and health policy researcher at Stanford University in California.

"Someone who eats a lot of fish probably doesn't eat a lot of meat," Henderson, who wasn't involved in the study, said by email. "Other research suggests that it is not just fish and meat that are important," he added.

Prior research on the Mediterranean diet has suggested that supplementing this diet with additional extra virgin olive oil may strengthen the connection to better cognitive function, Henderson noted.

For example, a long-term Spanish study linked a Mediterranean diet with extra nuts and olive oil to improved memory in older adults in a report published earlier this year.

While previous research has linked a Mediterranean diet to a reduced risk of heart disease and some cancers, as well as lower odds of developing Alzheimer's disease, scientists haven't conclusively proven that the diet itself is responsible, rather than other lifestyle choices made by people who eat this way.

"It is safe to say that a well-balanced diet such as the Mediterranean diet is a healthy diet, and this research provides exciting new support for this common-sense perspective," Henderson said. "Still, from my perspective, more clinical trial results are needed for a more specific take-home message."