Pass the olive oil. Fans of the Mediterranean Diet have one more reason to celebrate: The diet known for being heart-healthy also might protect aging brains from dementia.

Those who follow a diet rich in fish, olive oil, nuts and fruits and vegetables tend to have less brain atrophy than those not on the diet. Putting this in layman’s terms: Their brains are bigger.

Researchers from Columbia University asked 674 people over the age of 80 who showed no signs of dementia about their diet. Then they scanned the subjects’ brains and examined their brain volume.

The results were striking: The brains of devotees of the Mediterranean Diet were 13.11 milliliters larger on average than those who did not eat that way, according to the scientists, who published their study in the journal Neurology.

For many doctors, the news confirms their beliefs that lifestyle choices can contribute to a healthier brain.

“It’s taking the research that was previously done on the Mediterranean Diet and taking it to the next level,” said Dr. Michael Rosenbloom, clinical director of the HealthPartners Center for Memory and Aging in St. Paul.

“We’ve known for years that those who adhere to the Mediterranean Diet — which refers to foods that are high in fish and olive oil (and low in saturated fats), plus lots of fruits and vegetables — that these individuals have a lower relative risk for developing dementia of all types later in life.”

What the new study shows, he said, is a connection to brain volumes. He called the findings “provocative.”

“It’s really interesting that this supposedly protective diet now is associated with decreased brain atrophy,” he said.

A cautionary note

Dr. David Knopman, an investigator with the Mayo Clinic Study of Aging, said the research is solid but he cautioned against overstating the Mediterranean Diet’s benefits on the brain.

“The risk is in overinterpreting it,” he said of the study. “It doesn’t say that if somebody who hasn’t been eating healthy up until age 65 suddenly becomes a Mediterranean Diet devotee that it’s necessarily going to help them.

“But what the study does say is that the folks in this study in New York who had presumably been following the diet for many years in fact had better brain volumes than people who followed a diet that was something other than the Mediterranean Diet.”

The brain starts to shrink in our 30s and continues across the adult life span, Knopman said. He noted that brain shrinkage is normal and does not equal loss of brain function.

“Many people maintain high mental function even while their brain is shrinking into the ninth and 10th decades of life,” he said. But in cases of dementia, the loss of brain volume is accelerated.

Maintaining mental sharpness is a hot topic. About 5 million people across the country live with Alzheimer’s — a number expected to more than double by 2050 as the population ages.

Exciting possibilities

The potential to prevent brain atrophy through diet is a significant finding, said Dr. Henry Emmons, a Minneapolis psychiatrist whose latest book, “Staying Sharp,” deals with how to stay mentally fit as we age.

“This is really important,” he said of the study. “It highlights two things about the Mediterranean Diet that are really good for the brain. One is that the brain shrinks with age for lots of reasons. If your blood sugar is a little bit too high, that is associated with brain atrophy. One of the real advantages of the Mediterranean Diet is that it’s filled with foods that help stabilize your blood sugar.

“The second thing that I think is really important is the Mediterranean Diet is filled with healthy fat. It’s giving the brain the kind of fat it needs.”

As with all diets, it’s difficult to pinpoint exactly what is attributable to the food and what results from other lifestyle aspects associated with people who typically follow that diet. For example, in Mediterranean countries, meals are social events and are eaten over a longer, relaxed period.

“We know those who are more physically active, those who are socially active — these are also protective factors against developing dementia later in life,” Rosenbloom said. “It may be because those individuals [on the Mediterranean Diet] are more health-conscious and therefore more likely to exercise.

“The fact that we can’t isolate this lifestyle vs. others also makes the picture more muddy.”