The Mediterranean diet can improve cognitive function in older adults, according to a recent study.

Research published online Monday in JAMA Internal Medicine found that the plant-based diet, supplemented with antioxidant-rich extra virgin olive oil or mixed nuts, can "counteract the effects of aging on the brain's ability to function," The Wall Street Journal reported.

"This was the first clinical, randomized study using a dietary pattern for good health," Emilio Ros, who led the study at Hospital Clinic, told The Wall Street Journal. "This clinical trial removes the bias and provides first-level evidence."

For the study, researchers collected and analyzed data from more than 400 people who were at high cardiovascular risk and were enrolled in the Prevencion con Dieta Mediterranea nutrition intervention.

One hundred and fifty-five of them were assigned to supplement a Mediterranean diet with one liter of extra virgin olive oil per week; 147 were assigned to supplement a Mediterranean diet with 30 grams per day of a mix of walnuts, hazelnuts and almonds; and 145 individuals were assigned to follow a low-fat control diet.

The study participants also took cognitive function tests at the start of the study, Fox News reported.

They found that those assigned to the low-fat control diet had a significant decrease from baseline in all composites of cognitive function. Compared with the control group, the memory composite improved significantly in the Mediterranean diet plus nuts, while the frontal and global cognition composites improved in the Mediterranean diet plus olive oil group.

Researchers note the changes for the two Mediterranean diet arms in each composite were more like each other than when comparing the individual Mediterranean diet groups with the low-fat diet control group.

"Present results with the Mediterranean diet are encouraging but further investigation is warranted," researchers concluded in the study.