Oil, fish and vegetables are known to keep the heart healthy, but a new study has found that the Mediterranean diet may help people with Alzheimer's disease live longer as well.

An American study revealed a Mediterranean diet may help people with Alzheimer's disease live longer than patients who eat traditional Western foods, known for being high in saturated fats and hydrogenated oils and lower in fruits and vegetables.

The research, published in the medical journal of the American Academy of Neurology, followed 192 people with Alzheimer's disease in New York for an average of four and a half years.

Researchers found that those who most closely followed a Mediterranean diet - characterised by higher intakes of plant foods and fish, moderate intake of wine and lower intake of animal products - were 76 percent less likely to die during the study period than those who strayed from the Greek and Italian-inspired menu.

Author of the research, Nikos Scarmeas of Columbia University Medical Center, said there were clear indicators that eating more healthy fats and fleshy fish could prolong patients' lives.

"The more closely people followed the Mediterranean diet, the more they reduced their mortality," he said.

"For example, Alzheimer's patients who adhered to the diet to a moderate degree lived an average 1.3 years longer than those people who least adhered to the diet. And those Alzheimer's patients who followed the diet very religiously lived an average four years longer."

Previous research by Mr Scarmeas and his colleagues has shown that healthy people who eat a Mediterranean diet lower their risk of developing Alzheimer's disease.

Studies have also found that healthy people who follow a Mediterranean diet live longer than those who eat a more traditional Western diet.

Mr Scarmeas said new benefits of eating like southern Europeans continued to surface.

"We need to do more research to determine whether eating a Mediterranean diet also helps Alzheimer's patients have slower rates of cognitive decline, maintain their daily living skills, and have a better quality of life."

The Mediterranean diet includes a high intake of vegetables, legumes, fruits, cereals, fish, monounsaturated fatty acids; a low intake of saturated fatty acids, dairy products, meat and poultry; and a mild to moderate amount of alcohol.

Earlier this month a study showed that eating these foods may help people with rheumatoid arthritis improve their symptoms. A number of studies have also linked the diet to a lower risk of heart disease.