In my mid 40's I started noticing a lessening of mental acuity like this - I used to be able to hold a number in my head and use it immediately, but I started needing to "check" it.

For instance - before, look at a 7 digit phone number and dial it. After - look at the 7 digit phone number, dial the first part, look again, dial the next part.

This type of very, very slow decline, and loss in energy was ongoing...until I started the carnivore diet. The brain fog didn't lift completely, and immediately, but for some people it does. For me it's been much more gradual, but very noticeable. The improvement that was more immediate is the increase in energy. That one factor alone will make me stick to this for a lifetime.

And just also seeing so many people my age eating the standard diet, or even the standard "healthy" diet, and being almost crippled, frequently ill, knee issues, all kinds of things.

I don't think you need to go all-in, on carnivore, you can get massive benefits from keto and low-carb as well.