We've heard it before, but new research is once again drawing a link between a diet rich in polyunsaturated fats and reduced risk of developing dementia.

This new research, from Columbia University in New York, will be published in the Archives of Neurology. It found that a diet rich in olive oil, nuts, fish, fruits and cruciferous and leafy green vegetables was linked to a lower risk of Alzheimer's disease and other dementias.

People who ate diets high in these foods had a 40 per cent lower risk of developing Alzheimer's disease compared with others, Yian Gu, an Alzheimer's disease researcher at Columbia University in New York and colleagues found.

While many of the brain-boosting foods are also found in the popular Mediterranean diet, the researchers found that study participants didn't have to strictly adhere to that diet in order, or prepare their food in the Mediterranean cooking style, to lower their dementia risk.

The researchers found that eating habits that shared many of the Mediterranean diet's nutrients seemed to protect against Alzheimer's.

Researchers followed more than 2,100 New York City residents over age 65 for about four years. None of the patients had signs of dementia at the start of the study and each was assessed at least three times during the study period.

The researchers asked the subjects to keep records of what they ate to assess their intake of seven nutrients:

  • saturated fat
  • monounsaturated fatty acids, such as those found in nuts and vegetable oil
  • Omega-3 and Omega-6 polyunsaturated fatty acids, such as those in fish
  • vitamin E
  • vitamin B12
  • folate

Among the group, 253 developed Alzheimer's.

Of the one-third (749) of subjects whose diets ranked highest in saturated fats and B12 (both found in red meat and high-fat dairy products) and lowest in the other nutrients, 117 subjects (16 per cent) developed Alzheimer's disease during the study.

Of the 682 subjects whose diets ranked in the top third of the group in intake of vitamin E, folate and poly- and monounsaturated fats, just 50 subjects (or 7 per cent) developed Alzheimer's disease.

They found that the diet pattern strongly accociated with lower Alzheimer's risk included a high intake of salad dressing, nuts, fish, tomatoes, poultry, cruciferous vegetables, fruits, and dark and green leafy vegetables, and a low intake of high-fat dairy, red meat, organ meat, and butter.