Eating a Mediterranean diet rich in fish and vegetables may help prevent your brain shrinking for as long as five years, new research suggests.

People who follow such a diet, which also involves consuming less meat and dairy products than average, end up with bigger brains and slow down the ageing process, according to the US study.

“These results are exciting, as they raise the possibility that people may potentially prevent brain shrinking and the effects of ageing on the brain simply by following a healthy diet,” said the lead author, Yian Gu, of Columbia University in New York.

Researchers looked at 674 people with an average age of 80 who lived in northern Manhattan and did not have dementia.

They found that the total brain volume of those who had closely followed a Mediterranean-style diet was on average 13.11 millilitres greater than that of those who had not done so.

Their grey matter volume was 5 millilitres greater, and their white matter 6.4 millilitres greater, than those who had not stuck to Mediterranean foods.

The difference between the two groups is equivalent to about five years of ageing, the authors said.

“The magnitude of the association with brain measures was relatively small. But when you consider that eating at least five of the recommended Mediterranean diet components has an association comparable to five years of age, that is substantial,” said Gu.

Having fish regularly and eating little meat was particularly effective. “Eating at least 3 to 5 ounces of fish weekly, or eating no more than 3.5 ounces of meat daily, may provide considerable protection against loss of brain cells equal to about three to four years of ageing,” Gu added.

The Mediterranean diet typically consists of large amounts of vegetables, pulses, fruit, cereal, fish and monounsaturated fatty acids such as olive oil. It also includes small amounts of meat, poultry, dairy products and saturated fatty acids, plus mild to moderate alcohol consumption.

The authors cautioned that their findings, published in the journal Neurology, do not prove conclusively that the Mediterranean diet prevents brain shrinkage and that it is merely an association.

However, two British dementia charities said it was further evidence that the Mediterranean diet may improve brain health.

“There is an increasing amount of evidence that eating a healthy diet rich in fish, vegetables, legumes and nuts is good for your brain,” said Dr James Pickett, the head of research at the Alzheimer’s Society. “This study delves further into the potential benefits that diet could have, but it does not prove that a Mediterranean-style diet can stop your brain from shrinking as you age.”

People hoping to reduce their risk of developing dementia should also quit smoking, exercise regularly and keep their blood pressure low, he said.

But Dr Laura Phipps, a spokeswoman for Alzheimer’s Research UK, expressed caution: “While this study suggests there is an association between eating a Mediterranean diet and brain volume in healthy older people, we don’t know whether these particular food choices alter dementia risk. It’s hard to know from this study what the underlying reason for the link between diet and brain volume might be, and what other factors may be involved.”

Age remains the biggest risk factor for dementia, but genetics and lifestyle also play a part, Phipps added.