A diet rich in fish, omega-3 oils, fruits and vegetables may lower the risk of dementia and Alzheimer's disease, according to a study in the journal Neurology.
A diet high in omega-6 rich oils, on the other hand could increase chances of developing memory problems, the researchers found.
For the study, researchers examined the diets of 8,085 men and women over the age of 65 in France who did not have dementia at the beginning of the study.
Over the next four years, 183 of the participants developed Alzheimer's disease; 98 developed other types of dementia.
The study found people who reported that they regularly consumed omega-3 rich oils, such as canola oil, flaxseed oil and walnut oil, reduced their risk of dementia by 60 per cent compared to people who did not regularly consume such oils.
Those who reported they ate fruits and vegetables daily also reduced their risk of dementia by 30 per cent compared to those who didn't regularly eat fruits and vegetables.
The study also found that people who ate fish at least once a week had a 35 per cent lower risk of Alzheimer's disease and 40 per cent lower risk of dementia -- but only if they did not carry the gene that increases the risk of Alzheimer's, called "apolipoprotein E4", or ApoE4.
"Given that most people do not carry the ApoE4 gene, these results could have considerable implications in terms of public health," said study author Pascale Barberger-Gateau, of Inserm, the French National Institute for Health and Medical Research, in Bordeaux, France.
"However, more research is needed to identify the optimal quantity and combination of nutrients which could be protective before implementing nutritional recommendations."
The study also found people who did not carry the ApoE4 gene and ate a diet characterized by regular use of omega-6 rich oils, such as sunflower or corn oil which are often used in deep-frying, but not omega-3 rich oils or fish were twice as likely to develop dementia compared to those who didn't eat omega-6 rich oils.
"While we've identified dietary patterns associated with lowering a person's risk of dementia or Alzheimer's, more research is needed to better understand the mechanisms of these nutrients involved in these apparently protective foods," said Barberger-Gateau.
