Vegans (especially those that also avoid unfermented soy and get enough B-12) have fewer incidents of Alzheimer's and other forms of old-age senility. New studies are showing that vegans who eat right have more energy and stamina later in life - no wonder East Asian seniors are so much more alert and active than American ones. The foremost of all liberties is the control over one's own mind!
Actually, the best argument I've heard for dementia, Alzheimer's, and other neurological disorders like Autism is because of non-organic meats, organic is supposedly fine. Apparently, the feed used for meat production usually has other rendered meat products in it, which go rancid. Essentially it turns herbivores into carrion feeders, which makes the meat-bearing animal sick from neurotoxin poisoning, due to bacteria putting out toxins contained in the feed. Their bodies swell, making them larger to dilute the toxins within their systems. We then eat that meat, ingesting the toxins ourselves. This is allegedly what makes prepubescent girls develop breasts before they should, retain babyfat, and adults become generally fat as
we swell to dilute the toxins. We also become less clear in thinking - again from the neurotoxins - and eventually fall into dementia in greater numbers, at earlier ages. In utero, this could be whats triggering the autism gene. Or, partly. There are probably a number of causes for that, but this is probably one.
Dementia is increasing at an alarming rate, the older generations like your grandparents probably spent half their lives eating organic meats. Just because thats how it was raised, locally - and it grazed. We're not so lucky, and grow from infancy eating engineered meats, and meats fed by rendered slaughterhouse products.
These neurotoxins are also supposedly the root cause of madcow disease, through several generations of breeding, the animal becomes more packed with denser levels, get slaughtered, eats feeds with denser levels, the process snowballs.
Traditional societies that don't use feeds, but have free-range meat don't have these effects in any numbers close to ours. Amish, etc. Similar societies can be found in south america and asia, where cattle and chicken feed is prohibitively expensive. Amish people live to be old, but not senile. Asians, same thing. Its those toxins, and other things like hydrogenated oils, which we can't metabolize. Within those societies, autism is practically zero.
Diets of traditional peoples all (often) contain meats, shellfish, lots of animals. They also go after "superfoods" like honey and nuts. These contain enzymes and other essential nutrients that are not found in every other local food available to them. So if they go well out of their way to gather a weird food that is lacking in most essential nutrition, its probably got a hidden benefit.
Soy is a part of the vegetarian diet that should be avoided. In moderation, you can handle it. But soy is in so much vegetarian stuff, they allege you're overindulging. You should attempt a soy free diet if you're a vegetarian, from what I've heard, simply because you get enough when trying to avoid it, because its the go-to additive in all things veggie.