There is no evidence saturated fat causes Alzheimer's disease. A "western diet" is far too general to conclude such a thing--especially since more Americans eat leaner cuts of meat, and more chicken and fish than ever in the last 50 years. Refined carbohydrates and insulin spikes, however, ARE implicated. Alzheimers is often referred to as "Type 3 Diabetes" and related to other diet-related metabolic diseases.