"In eastern Asia, where soy foods are staples, rates of dementia in old age are lower than they are in Europe, where soy foods are uncommon."
I don't believe that soy foods are uncommon in Europe. I think Europe is much like the US, where approximately 80% of prepared foods have soy additives. (When you read "protein additive" on a label, that's usually soy.)
Furthermore, the processing of soy probably makes a huge difference - fermented/processed soy eaten in Asia is very different from non or improperly processed soy additives in American foods.
Also, the question arises: How do male vs female rates of dementia compare in East Asia?
I agree that there may be something else going on. E.g. Maybe milk-drinking (which westerners do more than east asians)
combined with tofu-eating causes brain atrophe. Maybe east asians are eating something (e.g. a lot of fish) which counteracts the soy.
Obviously, a lot more study is needed to reach any solid conclusions. Meanwhile, I'll try to avoid soy products.