People who ate nutrients specifically selected for brain health had a 40 percent 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.
Diet is probably the easiest way to modify disease risk, said Gu, whose study appears in Archives of Neurology.
She said because there are no cures for Alzheimer's, prevention is key, especially as the population ages.
If we follow this diet, that means the risk of getting the disease will be lowered for the population, Gu said in a telephone interview.
While other studies have looked at individual nutrients, Gu's team studied groups of foods high in nutrients that have been shown to be associated with Alzheimer's disease risk.
Some, such as saturated fatty acids in red meat and butter, need to be avoided. Others, such as omega-3 fatty acids, omega-6 fatty acids, vitamin E, vitamin B12 and folate, benefit the brain.
To study this, the team collected information on the diets of 2,148 healthy people over 65 for an average of 4 years. They were checked for Alzheimer's disease every 18 months.
Of these, 253 developed Alzheimer's, which has no cure.
Those least likely to develop the disease ate more olive oil-based salad dressing, nuts, fish, tomatoes, poultry, cruciferous vegetables such as broccoli, fruits, and dark and green leafy vegetables and ate less red meat, organ meat or high-fat dairy products.
People who adhered mostly to this dietary pattern compared to others have about a 40 percent reduction in the risk of developing Alzheimer's disease, Gu said.
She said the diet likely works in two ways. Because it is rich in heart-healthy foods, it may be protecting the brain from strokes that could make it more vulnerable to Alzheimer's disease.
But it also may be that the nutrients -- such as omega-3 fatty acids, antioxidants and folate -- directly protect the brain.
Current treatments helps with some symptoms, but cannot reverse the course of Alzheimer's, a mind-robbing form of dementia that affects more than 26 million people globally.