Not many people believe it though. 

My brain has had problems since about 4 years old. Long as I can remember, LOL

And it hasn't gotten better. ;-)

My personal belief is, based on what I think I have learned, that anything that causes huge blood glucose spikes or extended elevated glucose levels or anything that keeps insulin levels artificially high is not good for health in general. That includes the entire circulatory system and all the organs that depend on it. Including the brain. So based on that belief, it makes sense that any diet that keeps blood sugar spikes and overall blood sugar and insulin level in better control should help any and all the organs that depend on it. So I would tend to agree with that assessment. 

It has been shown in more than one study that ketones can help a person who already has Alzheimer's. Either via a ketogenic diet or by taking exogenous ketone supplement. The brain seems to have quit working as well on glucose but can still take up ketones for energy, That being the known case, it would stand to reason that providing the brain ketones via diet and at the same time lowering overloading the system with glucose by better sugar control would lead to a lessening chance of ever getting the disease. And that will always just be a theory because no way to have actual randomized controlled trials to see if it is true. Too many years to run the test and how to justify the ones that are getting the disease.

My personal belief is that no one should be eating over about an average of 125 grams of carbs a day. I'm not saying that at a birthday celebration of special occasion a person can't go past that for a few days out of the year. I'm saying on average eating days no one should be above that level for long term health. If a person follows current government food guidelines it is more like 300 grams a day. So my opinion is (and it is opinion only) nearly everyone is eating too many carbs.

In my particular situation, being diabetic (which means my metabolic health is poor), I keep the carb level generally at 20 grams or less to control my diabetic blood sugar level without drugs or insulin shots. Not everyone needs to be that strict. I actually now am testing pre-diabetic levels (A1c 6.0) rather than diabetic after being diabetic for over 30 years.

Yes, I am thinking this will help prevent things like Alzheimer's as well as heart disease, fatty liver and about all other non-infectious diseases. I know first hand that a close friend of mine is controlling her Parkinson's to a large degree with a ketogenic (close to carnivore) diet (in addition to regular exercise regime and some high dose certain B vitamins). I would estimate she has about 90% control of symptoms and most people would never know she has Parkinson's. This was from a beginning point of it being nearly debilitating. Her husband reversed his diabetes and no longer tests diabetic. They claim my wife and I saved their lives. All we did was set an example with them seeing the results of our first year of a ketogenic diet so they decided to try it also (after seeing our one year results). We started just over 5 years ago and they are now about 4 years on the very low carb ketogenic diet.

So those are my thoughts, experience and observation on the subject. I am not a doctor. I am not a dietitian. Just a dumb, high school educated dirt farmer, retired. Anyone would be a fool for doing anything just because I do it. I have made more mistakes in my life that I can even count. This may turn out to be one of them. Everyone needs to do their own research and due diligence. I only discuss and post what I do because it has helped me sooooo much in terms of health improvement (my wife's health also improved considerably as well as her weight loss). If the discussion can lead anyone else to do their own research and do some changes that improve their health, that is my hope that someone else can benefit the way I have. My way of trying to give back.

That is what I think I know, subject to change as I hopefully learn more.