A small scientific study of New York Alzheimer patients demonstrated significant increase in lifespan in those who had the highest adherence to the Mediterranean diet. 192 community-based individuals were followed for an average of 4.4 years (up to 13.6 years). They were divided into three groups of Mediterranean diet adherence: low, medium, and high. Compared to the people with low adherence, the others lived between 1 and 4 years longer. Those with highest adherence lived the longest, suggesting a dose-response effect like we would see with many drugs. No other diet has demonstrated this effect.
This same research group had previously reported that the Mediterranean diet lowered the risk for developing Alzheimer Disease in the first place.
Unfortunately, they did not report on whether the Mediterranean diet helped preserve brain function. (Don’t be surprised if that appears in a future journal article.) Prolongation of life by itself may be more of a curse than a blessing in advanced Alzheimer Disease.