WEDNESDAY, May 16, 2018 (HealthDay News) — You go to the gym to make your muscles bigger, but what if you want to bulk up your brain to help you stay sharp? New research suggests you might want to head to the produce aisle.

People who ate diets full of vegetables, fruits, nuts and fish had bigger brains than their less well-nourished counterparts, the large study from the Netherlands found.

“Adhering to an overall healthy diet quality supports brain health and might be a suitable preventive strategy to maintain and augment cognition [thinking and memory] in healthy older adults,” said the study’s senior author, Dr. Meike Vernooij. She’s a professor of population imaging at Erasmus University Medical Center, in Rotterdam.

The study included more than 4,200 people aged 45 and older at the start. Average age was 66, the researchers said.

Study volunteers completed a survey about what types and how much food they ate over the past month. The survey included almost 400 food items.

The researchers looked at diet quality based on Dutch dietary guidelines. Diet quality was measured on a scale of zero to 14, with 14 the healthiest. The best diets contained lots of fruits and vegetables, nuts, whole grains, dairy and fish, and limited sugary beverages, the researchers said.

The average diet score was seven, the study found.

Participants also had MRI scans done to measure their brain size. Information was also collected about other factors that could affect brain size, such as high blood pressure, physical activity and smoking.

After adjusting the data to account for such factors, the researchers saw that a higher diet score was linked to larger brain volume. Folks with the healthiest diets had brains that were about 2 milliliters larger than those who ate fewer healthy foods.

Could a 2 milliliter (mL) difference in brain size actually translate to better thinking and memory skills? The researchers said yes, it seems to.

“It is known that the risk of cognitive decline increases with advancing age. Moreover, with increasing age our brain volume decreases,” Vernooij said.

“In our population, a one-year increase in age was associated with a decrease in total brain volume of 3.66 mL, so the difference in brain volume we found is in the same order of magnitude as approximately six months’ increase in age [for those with the less healthy diet],” she explained.

But Vernooij also noted that the study cannot prove a cause-and-effect relationship; it was only designed to look for an association between diet and brain size.

When the researchers looked at the so-called Mediterranean diet — a plan that’s also full of produce, fish and nuts — they found similar results, with healthier eating tied to bigger brains.

How does a good diet help the brain?

It’s possible that good nutrition in youth — when the brain is developing and growing — may lead to a larger brain. And it’s possible that the people who ate a healthy diet in the study have been eating well since they were young, the researchers suggested.

James Hendrix, director of global science initiatives at the Alzheimer’s Association, said a healthy diet might lead to better blood flow.

“We think what’s good for the heart is good for the brain. If your heart is working well and getting good blood flow to the brain, the brain will be working better,” he said.

“One hypothesis of Alzheimer’s is that amyloid and tau proteins build up because they’re not being cleared properly. It may be that the brain needs good blood flow to clear out those proteins,” he suggested.

Hendrix said it’s important to note that there wasn’t one healthy food that made a difference, but rather a healthy diet overall.

“In the U.S., we love to find simple answers, but this is saying it’s all the things you’re eating, so let’s put some fish and leafy greens and whole grains into your diet,” he said.

The findings were published online May 16 in the journal Neurology.

More information

Learn more about brain health from the Alzheimer’s Association.