Get your olive oil (make sure it's the real Mackoy - be obnoxious about it if you have to be to find out what's in it), eat lots of healthy fats, and a variety of healthy food.   Indulge a sweet tooth occasionally.  Eat small amounts of red meat once or twice a week.

Get screened for nutrient deficiencies.   Metabolic problems that inhibit the absorption and use of various critical nutrients are behind many cases of dementia.