Mediterranean diet may help counteract age-related declines in memory and thinking skills

Julie Corliss
Julie Corliss, Executive Editor, Harvard Heart Letter

When I make a salad, I drizzle olive oil onto it and toss in a handful of toasted walnuts. Could this simple, tasty habit help me stay mentally sharp in the coming years? Maybe so. A new study in this week’s JAMA Internal Medicine suggests that eating a Mediterranean-style diet enhanced with extra-virgin olive oil or nuts is good for your mind as well as your heart.

These findings, which come from a long-term clinical trial of different diets, are the first ever to show possible brain-related benefits of one eating pattern over another.

The participants were part of a large Spanish trial known as PREDIMED, short for Prevención con Dieta Mediterránea (which means “prevention with Mediterranean diet”). The plant-based Mediterranean diet focuses mainly on fruits, vegetables, whole grains, beans and other legumes, nuts, seeds, and olive oil. It also features moderate amounts of seafood, poultry, eggs, and dairy, but includes only scant helpings of red meat and sweets.

The participants were mostly in their 60s and 70s and were at risk for developing heart disease. Most were overweight and many had high blood pressure or high cholesterol. They were divided into three groups: one followed a Mediterranean-type diet and also ate an extra ounce of mixed nuts (walnuts, hazelnuts, and almonds) a day; another followed a Mediterranean-type diet and also ate an extra five tablespoons of extra-virgin olive oil a day; the third group, which served as the control, followed a low-fat diet.

All 447 participants in this part of the PREDIMED trial took six different tests of cognitive function — a combination of memory and thinking skills — at the start of the trial. Three-quarters of them completed the same tests again about four years later.

In the control group, average scores on both types of tests — memory and thinking skills — fell during those four years. By comparison, average scores on the memory tests improved among those following the Mediterranean-type diet with extra servings of nuts, while scores on the tests of thinking skills improved among those following the Mediterranean diet with extra servings of olive oil.

Although the results of this study are promising, it’s important to keep a few caveats in mind: This study included only a small fraction (6%) of all the PREDIMED participants. The trial wasn’t designed to look at connections between diet and brain health. And one-quarter of the participants never took the second round of tests. All of this means the results need to be taken with a grain of salt.

How might olive oil and nuts help?

Extra-virgin olive oil and nuts contain compounds called polyphenols. These substances help quell oxidation and inflammation, which are harmful to blood vessels and the brain. This may explain why diets rich in polyphenols seem to prevent both heart disease and age-related cognitive problems, says Dr. Olivia Okereke, an assistant professor of psychiatry at Harvard Medical School. Her research focuses on lifestyle factors that contribute to late-life cognitive decline.

Researchers have long appreciated links between the circulatory system and the mind. “It makes sense because the brain is an oxygen-hungry organ. You need healthy blood vessels for a healthy brain,” says Dr. Okereke.

The new findings are consistent with earlier studies showing that people who closely follow a Mediterranean diet are more likely to maintain their memory and thinking skills over time. Still, the authors and other experts concur that further research is warranted. Dr. Okereke is curious about what seem to be the different effects of olive oil and nuts. “It would be great if future studies of this type could link to neuroimaging to see how and where these different foods create the specific cognitive performance changes seen in the study,” she says.

To date, there’s no evidence of any downside to eating olive oil, nuts, or a full Mediterranean diet, unless you end up taking in more calories than you need and gain weight. So I’ll keep enjoying my salads and look forward to learning about — and remembering — new research on the Mediterranean diet in the future.