We recommend what has been called the “Mind Diet.”  This is a diet focused on fruit, nuts, green leafy vegetables, other vegetables (not potatoes or French fries), whole grain foods, plant-based oils (e.g., olive oil), fish and poultry (no focus on beef or pork, i.e., avoid their fat), and little sugary foods and drinks.  Also, limited salt and limited (very limited) alcoholic beverages.
The Mind Diet (and those very similar to it) has been shown to reduce the risk of developing Alzheimer’s disease and other diseases common to aging adults. The following is a book listed in the Book Store and here.