Based on the evidence which is possible to find in the scientific literature here some guidelines for preventing Alzheimer’s disease. These guidelines are summarized and discussed in this interesting recent paper by Barnard et al. Neurobiology of aging 35(2014) : S74-S78
1. Minimize your intake of saturated fats and trans fats. Saturated fat is found primarily in dairy products, meats, and certain oils (coconut and palm oils). Trans fats are found in many snack pastries and fried foods and are listed on labels as “partially hydrogenated oils.”
2. Vegetables, legumes (beans, peas, and lentils), fruits, and whole grains should replace meats and dairy products as primary staples of the diet.
3. Vitamin E should come from foods, rather than supplements. Healthful food sources of vitamin E include seeds, nuts, green leafy vegetables, and whole grains. The recommended dietary allowance (RDA) for vitamin E is 15 mg per day.
4. A reliable source of vitamin B12, such as fortiﬁed foods or a supplement providing at least the recommended daily allowance (2.4 mg per day for adults), should be part of your daily diet. Have your blood levels of vitamin B12 checked regularly as many factors, including age, may impair absorption.
5. If using multiple vitamins, choose those without iron and copper and consume iron supplements only when directed by your physician.
6. Although aluminum’s role in Alzheimer’s disease remains a matter of investigation, those who desire to minimize their exposure can avoid the use of cookware, antacids, baking powder, or other products that contain aluminum.
7. Include aerobic exercise in your routine, equivalent to 40 minutes of brisk walking 3 times per week.
I would add: be active intellectually by all the possible means