At Rush, he met the Mind diet inventor, nutritional epidemiologist Martha Clare Morris, who took him on as a doctor-scientist, enabling him to work on the Mind diet trial while doing his own research.

Mind is an acronym for a combined approach to eating: Mediterranean-Dash intervention for neurodegenerative delay.

Dash stands for dietary approaches to stop hypertension. Foods in the Dash diet are rich in potassium, calcium and magnesium.

The Dash diet focuses on vegetables, fruits and whole grains, and includes fat-free or low-fat dairy products, fish, poultry, beans and nuts.

It limits foods that are high in salt, added sugar and saturated fat, such as in fatty meats and full-fat dairy products.

The Mediterranean diet emphasises plant-based foods and healthy fats. You eat mostly vegetables, fruits and whole grains. Olive oil is the main source of fat.

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Around 17 in every 1,000 participants who were committed to a Mediterranean diet developed dementia during a nine-year study follow-up period. For those who had the highest level of adherence to the Mediterranean diet, only around 12 out of every 1,000 developed dementia.

In many Western countries, he says, including the UK, people typically have quite a poor commitment to eating this way.

There are cardiovascular benefits of the Mediterranean diet that could contribute towards the benefits to brain health, Shannon says; what’s good for the heart tends to be good for the brain, too.

Holland says there are additional benefits, especially when you consider the Dash element of the Mind diet – and knowing that hypertension is a risk factor for dementia listed in medical journal The Lancet.

But there’s something else, he says: biochemical processes in our body cause cellular, and eventually, organ-level damage.

“We call this damage to the cells oxidative stress. When we ingest foods that contain antioxidants (like vitamins A, C, E, and flavonoids), especially those foods found in the Mind diet, the antioxidants act as reducing agents and essentially ‘destroy’ those free radicals and prevent further cellular damage.”

In addition, the nutrients in Mind diet foods also have anti-inflammatory properties.

“Although inflammation is a natural process in our bodies, necessary for multiple immune responses, sustained or over-activation of our immune system can also cause damage” – including to our brains, Holland says.

Eating foods that contain nutrients with anti-inflammatory properties can potentially prevent the over-activation or continued response of inflammatory cells and prevent cellular damage.

Ideal foods include dark leafy greens and other vegetables, nuts, berries, beans, whole grains, fish, poultry, and extra virgin olive oil or equivalent oil.

Foods to avoid – and certainly to avoid eating in excess – are red and processed meats, butter or margarine, high-fat cheese, fried foods and fast foods, and pastries and confectionery.

It’s not just about eating the right stuff, it’s also about avoiding the wrong foods.

One important component to this way of eating, says Holland, is to reduce your intake of trans-fatty acids that can eventually lead to fatty streaks and, more concerning, fatty plaques that can decrease blood flow, and at worst, rupture and cause heart attacks or strokes. Any cardiovascular event is also a threat to the brain’s health.

Holland’s advice is to do your best to avoid bad foods while optimising your intake of good ones. That’s because a good diet, like the Mind diet, slows the rate of cognitive decline, the incidence of Alzheimer’s dementia, and the burden of Alzheimer’s type of neuropathology.

A poor diet, like many Western type diets which are heavily reliant on fast food, can lead to the opposite: greater cognitive decline, more Alzheimer’s dementia, and more neuropathological burden.

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The good news, he says, is that even small changes, “like using olive oil as a cooking fat or adding a few more vegetables to a meal could make a big difference to someone’s Mediterranean diet score”.

But do remember, says Holland, that while diet is definitely a key factor, it’s just one component of a healthy lifestyle.

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“Appropriate control of blood sugars and blood pressure are also important for brain health, along with going to your primary care doctor once a year for a medical evaluation.”

Of his own attitude to brain health, Holland says: “I do work hard to practise what I prescribe by exercising four to six times a week, and eating well, although, I admit I can do a bit more cardio, and eat a wider array of vegetables.”

Do people in the Mediterranean have a lower incidence of cognitive decline with age?

It can be difficult to make comparisons of the prevalence of dementia between countries, says Shannon. But he stresses that “within Mediterranean countries, individuals who most closely follow the traditional Mediterranean diet tend to have lower rates of dementia”.