@gollum,
I looked for results from the Amish center and, while there was a lot of bullshit about the difficulties in coordinating any meaningful statistics (because the Amish are NOT a monolithic community nd are of late, just as guilty as any other group to dietary goof-ups), those of the Ag related groups(Old order Amish) seem to have a slight but statistically significant protection from developing Alzheimers.
My neighbors, a growing community of old order Amish with large families , have been gradually shifting from Dairy farming to beef cattle, market vegetable farming, and TOBACCO farming. They seem to maintain a dietary range that keeps up the old Pa German recipes that are high in fats and sugars,(even though these diets are loaded with fruits and veggies,). A typical supper may include chicken, meat dumplings, various starch dishes , cooked veggies usually with some kind of sauce that celebrates "sweet and sourness" and always som kind of sugary dessert.
Since we do little favors back and forth, we are always gifted with fruit pies, because, if you know, the old orderAmish have worship gatherings at each members home every two weeks. The worship services have a strong component of fellowship. So when the actual services end, the community meals begin and involve a heavy lunch and a light supper after an afternoon of bullshit and just visiting. These meals are generally dessert centered.
Although, having said that, I dont know of any reports of Alzheimer care or centers that their communities invest in. (They do believe in modern medicine as well as some degree of "folk med").
There are several Amish(self supported) med centers in Lancaster county in which their community members are givn primary care and are "triaged" for more serious (often genetically connected) medical problems.
We have a large Hispanic community also and, since thir diets are legend, we see lots of evidence of med problems associated with obesity in this community. I love Mxican and Tex Mex food but healthy it aint. I think if I lived on such a diet Id be back at 250.