Eating a Mediterranean diet that is rich in fish, vegetables and olive oil may protect the brain from protein build up and shrinkage that can lead to Alzheimer’s disease, new research suggests.

The study looked at abnormal proteins called amyloid and tau.

Amyloid is a protein that forms into plaques, while tau is a protein that forms into tangles.

They are both found in the brains of people with Alzheimer’s disease but may also be found in the brains of older people with normal cognition.

These results add to the body of evidence that show what you eat may influence your memory skills later on

The Mediterranean diet includes a high intake of vegetables, legumes, fruits, cereals, fish and monounsaturated fatty acids such as olive oil, and low intake of saturated fatty acids, dairy products and meat.

Study author Tommaso Ballarini, of the German Centre for Neurodegenerative Diseases (DZNE) in Bonn, Germany, said: “Our study suggests that eating a diet that’s high in unsaturated fats, fish, fruits and vegetables, and low in dairy and red meat may actually protect your brain from the protein build-up that can lead to memory loss and dementia.

“These results add to the body of evidence that show what you eat may influence your memory skills later on.”

Researchers looked at 512 people – 169 of whom were cognitively normal, while 343 were identified as being at higher risk of developing Alzheimer’s disease.

They analysed how closely people followed the Mediterranean diet based on their answers to a questionnaire asking how much they ate of 148 items over the previous month.

People who often ate healthy foods typical of the Mediterranean diet, like fish, vegetables and fruit, and only occasionally ate foods non-typical of the Mediterranean diet, like red meat, received the highest scores, for a maximum score of nine.

Cognitive skills were assessed with an extensive test set for Alzheimer’s disease progression that looked at five different functions, including language, memory and executive function.

All of the participants had brain scans to determine their brain volume, and the spinal fluid of 226 was tested for amyloid and tau protein biomarkers.

The study then looked at how closely someone followed the Mediterranean diet, and the relationship to both their brain volume, tau and amyloid biomarkers, and cognitive skills.

After adjusting for factors like age, sex and education, researchers found that in the area of the brain most closely associated with Alzheimer’s disease, every point lower people scored on the Mediterranean diet scale was equal to almost one year of brain ageing.

When looking at amyloid and tau in people’s spinal fluid, those who did not follow the diet closely had higher levels of biomarkers of amyloid and tau pathology than those who did.

People who did not follow the diet closely scored worse than those who did in a memory test.

The researchers say one limitation of their study is the fact that people’s diets were self-reported in the questionnaire, and they may have made errors recalling exactly what and how much they ate.

The research is published in Neurology, the medical journal of the American Academy of Neurology.