It seems that people who eat plenty of fruit, vegetables, whole grains and fish, drink a moderate amount of red wine and cook with olive oil, are 68 per cent less likely to suffer Alzheimer's than those who do not.
A Mediterranean diet has long been associated with a longer life and thought to help to stave off cancer, obesity and coronary heart disease, but scientists at the Columbia University Medical Centre in New York, say its effect against Alzheimer's appears to work independently.
Alzheimer's disease is a severely debilitating condition that affects thinking, learning and memory.
It begins with declines in memory about events in one's own life, and although medications are available to treat the symptoms, the drugs do not affect the underlying cause and progression of the disease.
Several studies have shown that eating fish, which is high in omega-3 fatty acids, may protect against Alzheimer's disease, which has prompted researchers to question whether supplements could have similar effects.
Scientists estimate that as many as 4.5 million Americans and 500,000 people in Britain, suffer from Alzheimer's disease.
The disease usually begins after age 60, and the risk goes up with age; the disease causes memory loss, mood changes and death.
For the study the Columbia team studied almost 1,984 adults and closely monitored them for signs of dementia every 18 months; they also examined their eating habits.
At the start of the study, of the participants, whose average age was 76, 194 had Alzheimer's and by the end another 89 had developed the disease.
They were given a score between 0 and 9 on how closely they stuck to a Mediterranean diet, and were divided into three groups according to their score.
The researchers found that those in the top group, who adhered most closely to a Mediterranean diet, were 68 per cent less likely to develop Alzheimer's compared with those in the bottom third.
Those in the middle group were 53 per cent less likely to get Alzheimer's than the bottom third.
The scientists calculated that for each additional point scored, the risk of Alzheimer's decreased by 19 to 24 per cent and the trends remained constant even after taking into account the participant's age, gender, ethnic background, weight and smoking history.
The diet's effect on individuals with diseases such as stroke, heart disease and diabetes, suggests, say the research team, that it might work through specific pathways to reduce Alzheimer's disease.
As far back as the 1950's the Mediterranean diet was thought to account for the long life expectancy of southern Europeans and in 2004 a team of Dutch researchers found that among the elderly, the diet was linked with a 23 per cent lower risk of death over ten years.
Experts say the Greeks stick most closely to the ideal Mediterranean diet, followed by the Spanish, Italians and French.
The research is published in the Archives of Neurology, a journal of the American Medical Association.