The Mediterranean diet is hailed by doctors and scientists for its menu of fruit, vegetables and wholegrains that has been shown to keep you sharp in old age. 

But now, scientists say a slightly tweaked version — packed with green tea, walnuts and a green smoothie — could even more effective in helping to slow brain ageing and slash the risk of dementia. 

Israeli researchers, who recruited more than 250 obese people to follow the diet, found it was effective in reducing high blood sugar levels and getting metabolism under control.

This, they discovered, offered 'neuroprotective benefits' and improved telltale signs of brain ageing on brain scans.

The findings show that maintaining a healthy weight and eating less processed foods 'may play a major role' in reducing neurodegeneration, the researchers said. 

The Mediterranean diet — high in healthy fats, proteins and wholegrains — has become extremely popular in recent years with a wealth of studies touting its benefits for longevity, reducing frailty and warding off cancer.

The diet involves largely shunning dairy, red meat and alcohol, while tucking into fruit, vegetables, wholegrains, olive oil, oily fish, nuts, seeds and pulses. 

Researchers at the Ben-Gurion University of the Negev recruited 284 volunteers, who were mostly men and aged 51, on average. 

They were asked to follow a 'green' Mediterranean diet for 18 months, which involved consuming 28g of walnuts daily, three to four cups of green tea and a green shake made with globosa — a plant extract.

Women were asked to consume no more than 1,200 to 1,400 calories a day, while men stuck to between 1,500 and 1,800 calories per day. 

MRI brain scans were completed at the start and end of the trial to calculate 'brain age' — how old the brain appears on scans, regardless of biological age. 

During the study, all participants received a free gym membership and educational sessions encouraging moderate-intensity physical activity.

Measurements were also taken of participants body weight, blood pressure and lipid levels.

They found those following the 'green' Mediterranean diet were most likely to see an improvement in their blood sugar levels (58.33 per cent).

The figure stood at 31.62 per cent among those on the Mediterranean diet and 28.57 per cent in the control group, suggesting those in the 'green' group were less likely to develop metabolic conditions like type 2 diabetes.

Writing in The American Journal of Clinical Nutrition, the researchers also said people following the green diet 'also had the most important improvements in the brain aging metrics'. 

They added: 'Increased consumption of green tea and Mankai shake [the green drink] was linked to greater improvements in brain health, especially in participants who consumed the shake at least thrice a week and drank green tea daily.'

This 'could be partially attributed to the high content of polyphenols that are present in plant-based food sources', they also said. 

These are a group of naturally occurring compounds found in plants that have antioxidant properties.

The scientists, however, acknowledged the research had 'a number of limitations' including a lack of data on volunteers' educational or cognitive status before the study began. 

The high proportion of male participants may also 'limit the generalisability of our findings to females', they said. 

Recent analysis by the Alzheimer's Society estimates the overall annual cost of the dementia to the UK is £42billion a year, with families bearing the brunt.

An ageing population means these costs – which include lost earnings of unpaid carers – are set to soar to £90billion in the next 15 years.

Around 944,000 in the UK are thought to be living with dementia, while the figure is thought to be around 7million in the US.

Alzheimer's affects around six in 10 people with dementia.

It is thought to be caused by a build-up of amyloid and tau in the brain, which clump together and from plaques and tangles that make it harder for the brain to work properly.

Eventually, the brain struggles to cope with this damage and dementia symptoms develop.

Memory problems, thinking and reasoning difficulties and language problems are common early symptoms of the condition, which then worsen over time.

Alzheimer's Research UK analysis found 74,261 people died from dementia in 2022 compared with 69,178 a year earlier, making it the country's biggest killer.